Rework into FTP scanning server

- Rename to Scanyonero - Add FTP server that ingests TIFF, PNG, JPEG or PDF files - Add web interface to check and modify ingested files - Rework how ocrmypdf is invoked Basics are working, but the program is not in a usable state.
2025-06-06 01:10:00 +00:00 · 2025-05-14 12:08:38 +02:00 · 2025-05-14 12:08:38 +02:00 · 853a1bb58d
commit 853a1bb58d
parent c82cd72a47
62 changed files with 2919 additions and 28 deletions
--- a/.gitignore
+++ b/.gitignore
@ -0,0 +1,76 @@
+# File created using '.gitignore Generator' for Visual Studio Code: https://bit.ly/vscode-gig
+# Created by https://www.toptal.com/developers/gitignore/api/windows,visualstudiocode,go
+# Edit at https://www.toptal.com/developers/gitignore?templates=windows,visualstudiocode,go
+
+### Go ###
+# If you prefer the allow list template instead of the deny list, see community template:
+# https://github.com/github/gitignore/blob/main/community/Golang/Go.AllowList.gitignore
+#
+# Binaries for programs and plugins
+*.exe
+*.exe~
+*.dll
+*.so
+*.dylib
+
+# Test binary, built with `go test -c`
+*.test
+
+# Output of the go coverage tool, specifically when used with LiteIDE
+*.out
+
+# Dependency directories (remove the comment below to include it)
+# vendor/
+
+# Go workspace file
+go.work
+
+### VisualStudioCode ###
+.vscode/*
+!.vscode/settings.json
+!.vscode/tasks.json
+!.vscode/launch.json
+!.vscode/extensions.json
+!.vscode/*.code-snippets
+
+# Local History for Visual Studio Code
+.history/
+
+# Built Visual Studio Code Extensions
+*.vsix
+
+### VisualStudioCode Patch ###
+# Ignore all local history of files
+.history
+.ionide
+
+### Windows ###
+# Windows thumbnail cache files
+Thumbs.db
+Thumbs.db:encryptable
+ehthumbs.db
+ehthumbs_vista.db
+
+# Dump file
+*.stackdump
+
+# Folder config file
+[Dd]esktop.ini
+
+# Recycle Bin used on file shares
+$RECYCLE.BIN/
+
+# Windows Installer files
+*.cab
+*.msi
+*.msix
+*.msm
+*.msp
+
+# Windows shortcuts
+*.lnk
+
+# End of https://www.toptal.com/developers/gitignore/api/windows,visualstudiocode,go
+
+# Custom rules (everything added below won't be overriden by 'Generate .gitignore File' if you use 'Update' option)
+
--- a/.vscode/launch.json
+++ b/.vscode/launch.json
@ -0,0 +1,24 @@
+{
+    // Use IntelliSense to learn about possible attributes.
+    // Hover to view descriptions of existing attributes.
+    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
+    "version": "0.2.0",
+    "configurations": [
+
+        {
+            "name": "Launch static/index.html",
+            "type": "firefox",
+            "request": "launch",
+            "reAttach": true,
+            "file": "${workspaceFolder}/static/index.html",
+        },
+        {
+            "name": "Launch Go application",
+            "type": "go",
+            "request": "launch",
+            "mode": "debug",
+            "program": "${workspaceFolder}",
+            "output": "${workspaceFolder}/debug_bin"
+        }
+    ]
+}
--- a/.vscode/settings.json
+++ b/.vscode/settings.json
@ -0,0 +1,21 @@
+{
+    "cSpell.words": [
+        "afero",
+        "EXTRACTIMAGES",
+        "fclairamb",
+        "ftpserver",
+        "ftpserverdriver",
+        "ftpserverlib",
+        "Ingestor",
+        "jfif",
+        "Millimetres",
+        "neilpa",
+        "pdfcpu",
+        "Scanyonero",
+        "Subed",
+        "Typer",
+        "typst",
+        "unitless",
+        "xhttp"
+    ]
+}
--- a/README.md
+++ b/README.md
@ -1,15 +1,19 @@
-# OCRmyPDF runner
+# Scanyonero

-A very simple tool that listens for files in a directory, and runs OCRmyPDF on them.
+A tool for preprocessing scanned documents before they are sent to paperless.
+Simply point your scanner to the FTP server this software provides, and it will do the rest.

-This is needed as paperless(-ngx) will always create a copy of the document with its built in clean up and OCR feature.
-Even external pre-consumption scripts will be run on all new documents, not just files in from consumption directory.
-So the solution is to have this watchdog/runner that only pre-processes scanned documents, and leaves everything else untouched.
+## Features

-The idea is to let it watch a directory any scanner will scan into, and then this runner will write the final pre-processed document into a directory paperless watches.
+- Built in FTP server, and therefore no need for temporary files or any other Rube Goldberg-esque setups.
+- Web-app where you can preview, sort, split and merge your scans before sending them to paperless.
+- Can use OCRmyPDF for adding searchable text to your scanned documents.
+- Can clean up documents and make them as pristine and compact as possible.

 ## Usage

+TODO: Update README.md
+
 1. Install the project somewhere.
 2. Edit [main.go](main.go) to use the correct paths to your scanner and paperless consumption directories.
 3. Copy the [ocrmypdf-runner.service](service/linux/systemd/ocrmypdf-runner.service) into your systemd services directory (`etc/systemd/system/ocrmypdf-runner.service`). You may have to change the user in the service file.
--- a/document/file.go
+++ b/document/file.go
@ -0,0 +1,37 @@
+package document
+
+import (
+	"fmt"
+	"log"
+	"os"
+)
+
+// File contains the raw data of a file coming from a scanner.
+type File struct {
+	Name string
+	Data []byte
+}
+
+// LoadFile reads a file and returns it as a File.
+func LoadFile(filename string) (File, error) {
+	data, err := os.ReadFile(filename)
+	if err != nil {
+		return File{}, fmt.Errorf("couldn't read file: %w", err)
+	}
+
+	return File{
+		Name: filename,
+		Data: data,
+	}, nil
+}
+
+// LoadFile reads a file and returns it as a File.
+// This will panic on any error.
+func MustLoadFile(filename string) File {
+	file, err := LoadFile(filename)
+	if err != nil {
+		log.Panicf("Failed to load file: %v.", err)
+	}
+
+	return file
+}
--- a/document/ingestor-rules.go
+++ b/document/ingestor-rules.go
@ -0,0 +1,56 @@
+package document
+
+import (
+	"Scanyonero/unit"
+	"regexp"
+)
+
+type IngestorRule struct {
+	// All entries that are non nil have to match.
+	Match struct {
+		Name    *regexp.Regexp // When this regular expression matches with the filename/filepath then the rule is used.
+		XPixels *int           // When the scanned image width in pixels matches with the given amount of pixels, the rule is used.
+		YPixels *int           // When the scanned image height in pixels matches with the given amount of pixels, the rule is used.
+	}
+
+	// All non nil entries will be applied to the document pages.
+	Action struct {
+		MediumWidth  *unit.Millimeter // Sets the width of the medium.
+		MediumHeight *unit.Millimeter // Sets the height of the medium.
+		ScanOffsetX  *unit.Millimeter // Offsets the scan in the medium on the x axis.
+		ScanOffsetY  *unit.Millimeter // Offsets the scan in the medium on the y axis.
+	}
+}
+
+// Apply will check and apply the rule per ingested page.
+func (rule IngestorRule) Apply(ingestor Ingestor, file File, page *Page) error {
+	// Match.
+
+	if rule.Match.Name != nil && !rule.Match.Name.MatchString(file.Name) {
+		return nil
+	}
+	imageBounds := page.Image.Bounds()
+	if rule.Match.XPixels != nil && *rule.Match.XPixels != imageBounds.Dx() {
+		return nil
+	}
+	if rule.Match.YPixels != nil && *rule.Match.YPixels != imageBounds.Dy() {
+		return nil
+	}
+
+	// Apply actions.
+
+	if rule.Action.MediumWidth != nil {
+		page.Dimensions.MediumSize.X = *rule.Action.MediumWidth
+	}
+	if rule.Action.MediumHeight != nil {
+		page.Dimensions.MediumSize.Y = *rule.Action.MediumHeight
+	}
+	if rule.Action.ScanOffsetX != nil {
+		page.Dimensions.ScanSize.Origin.X = *rule.Action.ScanOffsetX
+	}
+	if rule.Action.ScanOffsetY != nil {
+		page.Dimensions.ScanSize.Origin.Y = *rule.Action.ScanOffsetY
+	}
+
+	return nil
+}
--- a/document/ingestor.go
+++ b/document/ingestor.go
@ -0,0 +1,138 @@
+package document
+
+import (
+	"Scanyonero/unit"
+	"bytes"
+	"fmt"
+	"image"
+	"path/filepath"
+	"strings"
+
+	"github.com/chai2010/tiff"
+	"github.com/pdfcpu/pdfcpu/pkg/api"
+	"github.com/pdfcpu/pdfcpu/pkg/pdfcpu"
+	"github.com/pdfcpu/pdfcpu/pkg/pdfcpu/model"
+
+	"image/jpeg"
+	"image/png"
+)
+
+// Ingestor contains all settings and rules for image/document file ingestion.
+type Ingestor struct {
+	DefaultDPI unit.PerInch // Default/fallback dots per inch value.
+
+	Rules []IngestorRule
+}
+
+func (ingestor Ingestor) Ingest(file File) ([]Page, error) {
+	ext := filepath.Ext(file.Name)
+
+	var pages []Page
+
+	switch strings.ToLower(ext) {
+	case ".jpg", ".jpeg":
+		img, err := jpeg.Decode(bytes.NewReader(file.Data))
+		if err != nil {
+			return nil, fmt.Errorf("failed to decode JPEG file: %w", err)
+		}
+		dimensions := unit.NewPageDimensionsFromDensity(img.Bounds().Dx(), img.Bounds().Dy(), ingestor.DefaultDPI, ingestor.DefaultDPI)
+		if tag, err := decodeJFIF(bytes.NewReader(file.Data)); err == nil {
+			// Get more exact density info from the file metadata.
+			xDensity, yDensity := tag.Density()
+			dimensions = unit.NewPageDimensionsFromDensity(img.Bounds().Dx(), img.Bounds().Dy(), xDensity, yDensity)
+		}
+		pages = append(pages, Page{
+			Image:      img,
+			Dimensions: dimensions,
+		})
+
+	case ".png":
+		img, err := png.Decode(bytes.NewReader(file.Data))
+		if err != nil {
+			return nil, fmt.Errorf("failed to decode PNG file: %w", err)
+		}
+		pages = append(pages, Page{
+			Image:      img,
+			Dimensions: unit.NewPageDimensionsFromDensity(img.Bounds().Dx(), img.Bounds().Dy(), ingestor.DefaultDPI, ingestor.DefaultDPI),
+		})
+		// TODO: Read pixel density metadata from PNG file
+
+	case ".tiff":
+		mm, _, err := tiff.DecodeAll(bytes.NewReader(file.Data))
+		if err != nil {
+			return nil, fmt.Errorf("failed to decode TIFF file: %w", err)
+		}
+		for _, m := range mm {
+			for _, img := range m {
+				pages = append(pages, Page{
+					Image:      img,
+					Dimensions: unit.NewPageDimensionsFromDensity(img.Bounds().Dx(), img.Bounds().Dy(), ingestor.DefaultDPI, ingestor.DefaultDPI),
+				})
+				// TODO: Read pixel density metadata from TIFF file
+			}
+		}
+
+	case ".pdf":
+		conf := model.NewDefaultConfiguration()
+		conf.Cmd = model.EXTRACTIMAGES
+		ctx, err := api.ReadValidateAndOptimize(bytes.NewReader(file.Data), conf)
+		if err != nil {
+			return nil, fmt.Errorf("failed to read and validate PDF file: %w", err)
+		}
+
+		boundaries, err := ctx.PageBoundaries(nil)
+		if err != nil {
+			return nil, fmt.Errorf("failed to get page dimensions: %w", err)
+		}
+		if len(boundaries) != ctx.PageCount {
+			return nil, fmt.Errorf("number of retrieved page boundaries (%d) and pages (%d) differ", len(boundaries), ctx.PageCount)
+		}
+
+		for page := 1; page <= ctx.PageCount; page++ {
+			mm, err := pdfcpu.ExtractPageImages(ctx, page, false)
+			if err != nil {
+				return nil, fmt.Errorf("failed to extract image from page: %w", err)
+			}
+			if len(mm) == 0 {
+				return nil, fmt.Errorf("page %d doesn't contain any images", page)
+			}
+			if len(mm) > 1 {
+				return nil, fmt.Errorf("page %d contains %d images, expected 1", page, len(mm))
+			}
+
+			boundary := boundaries[page-1]
+			dim := boundary.Media.Rect.Dimensions().ToMillimetres()
+			dimX, dimY := unit.Millimeter(dim.Width), unit.Millimeter(dim.Height)
+
+			// Decode only image of the page.
+			for _, m := range mm {
+				img, _, err := image.Decode(m)
+				if err != nil {
+					return nil, fmt.Errorf("failed to decode %q file: %w", ext, err)
+				}
+
+				pages = append(pages, Page{
+					Image:      img,
+					Dimensions: unit.NewPageDimensionsFromLengths(dimX, dimY),
+				})
+
+				break
+			}
+
+		}
+
+	default:
+		return nil, fmt.Errorf("unsupported file extension %q", ext)
+	}
+
+	for iPage := range pages {
+		page := &pages[iPage]
+		for i, rule := range ingestor.Rules {
+			if err := rule.Apply(ingestor, file, page); err != nil {
+				return nil, fmt.Errorf("failed to apply ingestor rule %d on page %d: %w", i, iPage, err)
+			}
+		}
+	}
+
+	return pages, nil
+}
--- a/document/ingestor_test.go
+++ b/document/ingestor_test.go
@ -0,0 +1,110 @@
+package document
+
+import (
+	"Scanyonero/unit"
+	"path/filepath"
+	"regexp"
+	"testing"
+)
+
+func TestIngestor_Ingest(t *testing.T) {
+	t.SkipNow()
+
+	tests := []struct {
+		name    string
+		file    File
+		want    []Page
+		wantErr bool
+	}{
+		{"300 DPI Feed JPG", MustLoadFile(filepath.Join("..", "test-documents", "300 DPI Feeder.jpg")),
+			[]Page{{
+				Dimensions: unit.PageDimensions[unit.Millimeter]{
+					ScanSize: unit.Rectangle[unit.Millimeter]{
+						Size: unit.Vec2[unit.Millimeter]{X: 209.97, Y: 288.713}}},
+			}}, false},
+		{"300 DPI Feed PDF", MustLoadFile(filepath.Join("..", "test-documents", "300 DPI Feeder.pdf")),
+			[]Page{{
+				Dimensions: unit.PageDimensions[unit.Millimeter]{
+					ScanSize: unit.Rectangle[unit.Millimeter]{
+						Size: unit.Vec2[unit.Millimeter]{X: 209.8, Y: 288.5}}},
+			}}, false},
+		{"300 DPI Flat JPG", MustLoadFile(filepath.Join("..", "test-documents", "300 DPI Flatbed.jpg")),
+			[]Page{{
+				Dimensions: unit.PageDimensions[unit.Millimeter]{
+					ScanSize: unit.Rectangle[unit.Millimeter]{
+						Size: unit.Vec2[unit.Millimeter]{X: 203.2, Y: 290.83}}},
+			}}, false},
+		{"300 DPI Flat PDF", MustLoadFile(filepath.Join("..", "test-documents", "300 DPI Flatbed.pdf")),
+			[]Page{{
+				Dimensions: unit.PageDimensions[unit.Millimeter]{
+					ScanSize: unit.Rectangle[unit.Millimeter]{
+						Size: unit.Vec2[unit.Millimeter]{X: 203.2, Y: 290.8}}},
+			}}, false},
+		{"600 DPI Feed JPG", MustLoadFile(filepath.Join("..", "test-documents", "600 DPI Feeder.jpg")),
+			[]Page{{
+				Dimensions: unit.PageDimensions[unit.Millimeter]{
+					ScanSize: unit.Rectangle[unit.Millimeter]{
+						Size: unit.Vec2[unit.Millimeter]{X: 209.97, Y: 288.671}}},
+			}}, false},
+		{"600 DPI Feed PDF", MustLoadFile(filepath.Join("..", "test-documents", "600 DPI Feeder.pdf")),
+			[]Page{{
+				Dimensions: unit.PageDimensions[unit.Millimeter]{
+					ScanSize: unit.Rectangle[unit.Millimeter]{
+						Size: unit.Vec2[unit.Millimeter]{X: 209.8, Y: 288.0}}},
+			}}, false},
+		{"600 DPI Flat JPG", MustLoadFile(filepath.Join("..", "test-documents", "600 DPI Flatbed.jpg")),
+			[]Page{{
+				Dimensions: unit.PageDimensions[unit.Millimeter]{
+					ScanSize: unit.Rectangle[unit.Millimeter]{
+						Size: unit.Vec2[unit.Millimeter]{X: 203.88, Y: 290.872}}},
+			}}, false},
+		{"600 DPI Flat PDF", MustLoadFile(filepath.Join("..", "test-documents", "600 DPI Flatbed.pdf")),
+			[]Page{{
+				Dimensions: unit.PageDimensions[unit.Millimeter]{
+					ScanSize: unit.Rectangle[unit.Millimeter]{
+						Size: unit.Vec2[unit.Millimeter]{X: 203.7, Y: 290.8}}},
+			}}, false},
+	}
+
+	ingestor := Ingestor{
+		DefaultDPI: unit.PerInch(150),
+		Rules: []IngestorRule{{
+			Match: struct {
+				Name    *regexp.Regexp
+				XPixels *int
+				YPixels *int
+			}{
+				Name: regexp.MustCompile(`^.*\.pdf$`),
+			},
+			Action: struct {
+				MediumWidth  *unit.Millimeter
+				MediumHeight *unit.Millimeter
+				ScanOffsetX  *unit.Millimeter
+				ScanOffsetY  *unit.Millimeter
+			}{
+				MediumWidth: &([]unit.Millimeter{100}[0]),
+			},
+		}},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := ingestor.Ingest(tt.file)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("Ingestor.Ingest() error = %v, wantErr %v.", err, tt.wantErr)
+				return
+			}
+			if len(got) != len(tt.want) {
+				t.Errorf("Got %d pages, but want %d pages.", len(got), len(tt.want))
+				return
+			}
+			for i, gotPage := range got {
+				wantPage := tt.want[i]
+				if !gotPage.Dimensions.ScanSize.Size.EqualWithPrecision(wantPage.Dimensions.ScanSize.Size, 0.1) {
+					t.Errorf("Resulting ScanSize is %v, want %v.", gotPage.Dimensions.ScanSize.Size, wantPage.Dimensions.ScanSize.Size)
+				}
+			}
+
+		})
+	}
+}
--- a/document/jfif.go
+++ b/document/jfif.go
@ -0,0 +1,72 @@
+package document
+
+import (
+	"Scanyonero/unit"
+	"encoding/binary"
+	"fmt"
+	"io"
+
+	"neilpa.me/go-jfif"
+)
+
+type jfifTagUnits byte
+
+const (
+	jfifTagUnitsNoUnits jfifTagUnits = iota
+	jfifTagUnitsDotsPerInch
+	jfifTagUnitsDotsPerCM
+)
+
+type jfifTag struct {
+	Version  uint16
+	Units    jfifTagUnits
+	XDensity uint16
+	YDensity uint16
+	// Omit thumbnail width, height and pixel data.
+}
+
+func (j *jfifTag) UnmarshalBinary(data []byte) error {
+	if len(data) < 7 {
+		return fmt.Errorf("JFIF tag length (%d) is smaller than expected (%d)", len(data), 7)
+	}
+
+	j.Version = binary.BigEndian.Uint16(data[0:2])
+	j.Units = jfifTagUnits(data[2])
+	j.XDensity = binary.BigEndian.Uint16(data[3:5])
+	j.YDensity = binary.BigEndian.Uint16(data[5:7])
+
+	return nil
+}
+
+// Density returns the number of pixels per length unit.
+func (j *jfifTag) Density() (x, y unit.Density) {
+	switch j.Units {
+	case jfifTagUnitsDotsPerInch:
+		return unit.PerInch(j.XDensity), unit.PerInch(j.YDensity)
+	case jfifTagUnitsDotsPerCM:
+		return unit.PerMillimeter(j.XDensity) / 10, unit.PerMillimeter(j.YDensity) / 10
+	}
+
+	return nil, nil
+}
+
+func decodeJFIF(r io.Reader) (jfifTag, error) {
+	segments, err := jfif.DecodeSegments(r)
+	if err != nil {
+		return jfifTag{}, fmt.Errorf("failed to decode JPEG segments: %w", err)
+	}
+
+	for _, segment := range segments {
+		sig, data, _ := segment.AppPayload()
+		switch sig {
+		case jfif.SigJFIF:
+			tag := jfifTag{}
+			if err := tag.UnmarshalBinary(data); err != nil {
+				return jfifTag{}, fmt.Errorf("failed to unmarshal tag data: %w", err)
+			}
+			return tag, nil
+		}
+	}
+
+	return jfifTag{}, fmt.Errorf("couldn't find any JFIF tag")
+}
--- a/document/page.go
+++ b/document/page.go
@ -0,0 +1,12 @@
+package document
+
+import (
+	"Scanyonero/unit"
+	"image"
+)
+
+type Page struct {
+	Image image.Image `json:"-"`
+
+	Dimensions unit.PageDimensions[unit.Millimeter] `json:"dimensions"`
+}
--- a/ftpserver/driver.go
+++ b/ftpserver/driver.go
@ -0,0 +1,57 @@
+package ftpserver
+
+import (
+	"crypto/tls"
+	"fmt"
+
+	ftpserver "github.com/fclairamb/ftpserverlib"
+	"github.com/spf13/afero"
+)
+
+type driver struct {
+	User, Pass string
+	ListenAddr string
+
+	ClientDriver afero.Fs
+}
+
+// GetSettings returns some general settings around the server setup
+func (d *driver) GetSettings() (*ftpserver.Settings, error) {
+	//log.Printf("Passed settings to ftpserverlib.")
+
+	return &ftpserver.Settings{
+		ListenAddr:          d.ListenAddr,
+		DefaultTransferType: ftpserver.TransferTypeBinary,
+	}, nil
+}
+
+// ClientConnected is called to send the very first welcome message
+func (d *driver) ClientConnected(cc ftpserver.ClientContext) (string, error) {
+	//log.Printf("Client %q connected.", cc.RemoteAddr())
+
+	return "Welcome to the Scanyonero FTP server.", nil
+}
+
+// ClientDisconnected is called when the user disconnects, even if he never authenticated
+func (d *driver) ClientDisconnected(cc ftpserver.ClientContext) {
+	//log.Printf("Client %q disconnected.", cc.RemoteAddr())
+}
+
+// AuthUser authenticates the user and selects an handling driver
+func (d *driver) AuthUser(cc ftpserver.ClientContext, user, pass string) (ftpserver.ClientDriver, error) {
+	if d.User != "" && d.Pass != "" {
+		if user != d.User || pass != d.Pass {
+			return nil, fmt.Errorf("wrong username or password")
+		}
+	}
+
+	//log.Printf("Client %q authenticated with %q and %q.", cc.RemoteAddr(), user, pass)
+
+	return d.ClientDriver, nil
+}
+
+// GetTLSConfig returns a TLS Certificate to use
+// The certificate could frequently change if we use something like "let's encrypt"
+func (d *driver) GetTLSConfig() (*tls.Config, error) {
+	return nil, fmt.Errorf("tls not implemented")
+}
--- a/ftpserver/driver_test.go
+++ b/ftpserver/driver_test.go
@ -0,0 +1,20 @@
+package ftpserver_test
+
+import (
+	"Scanyonero/ftpserver"
+	"log"
+	"testing"
+)
+
+func TestDriver(t *testing.T) {
+	t.SkipNow()
+
+	server, err := ftpserver.NewFTPServer("", "", "127.0.0.1:21")
+	if err != nil {
+		log.Panicf("Failed to create FTP-Server: %v.", err)
+	}
+
+	for file := range server.FileChan() {
+		log.Printf("Received file %v with %d bytes.", file.Name, len(file.Data))
+	}
+}
--- a/ftpserver/ftp-server.go
+++ b/ftpserver/ftp-server.go
@ -0,0 +1,80 @@
+package ftpserver
+
+import (
+	"Scanyonero/document"
+	"fmt"
+	"sync"
+
+	ftpserverlib "github.com/fclairamb/ftpserverlib"
+)
+
+type FTPServer struct {
+	files chan document.File
+
+	ftpServer *ftpserverlib.FtpServer
+}
+
+// NewFTPServer returns a new FTP server instance.
+// This will also start the server.
+func NewFTPServer(user, pass, listenAddr string) (*FTPServer, error) {
+	fs := &virtualFS{}
+
+	driver := &driver{
+		User:         user,
+		Pass:         pass,
+		ListenAddr:   listenAddr,
+		ClientDriver: fs,
+	}
+
+	s := &FTPServer{
+		files:     make(chan document.File),
+		ftpServer: ftpserverlib.NewFtpServer(driver),
+	}
+
+	// Handler callback for newly uploaded files.
+	// We will pass the files into the files channel.
+	var closed bool
+	var mutex sync.Mutex
+	fs.Callback = func(file document.File) error {
+		mutex.Lock()
+		defer mutex.Unlock()
+		if closed {
+			return fmt.Errorf("server is closing")
+		}
+
+		s.files <- file
+		return nil
+	}
+
+	// Create listener.
+	if err := s.ftpServer.Listen(); err != nil {
+		return nil, err
+	}
+
+	// Start listening.
+	go func() {
+		s.ftpServer.Serve()
+
+		// We will be shutting down everything soon.
+		// Ensure that no new files will be written into the files channel.
+		mutex.Lock()
+		closed = true
+		mutex.Unlock()
+
+		close(s.files)
+	}()
+
+	return s, nil
+}
+
+// Returns the file channel where files uploaded to the FTP-Server will be sent to.
+//
+// The channel will automatically be closed after Stop() has been called.
+func (s *FTPServer) FileChan() <-chan document.File {
+	return s.files
+}
+
+// Shuts the FTP-Server down.
+func (s *FTPServer) Stop() error {
+	return s.ftpServer.Stop()
+}
--- a/ftpserver/utils.go
+++ b/ftpserver/utils.go
@ -0,0 +1,16 @@
+package ftpserver
+
+import "path/filepath"
+
+func normalizePath(path string) string {
+	path = filepath.Clean(path)
+
+	switch path {
+	case ".":
+		return string(filePathSeparator)
+	case "..":
+		return string(filePathSeparator)
+	default:
+		return path
+	}
+}
--- a/ftpserver/virtual-fs.go
+++ b/ftpserver/virtual-fs.go
@ -0,0 +1,146 @@
+package ftpserver
+
+import (
+	"Scanyonero/document"
+	"io"
+	"os"
+	"time"
+
+	"github.com/spf13/afero"
+	"github.com/spf13/afero/mem"
+)
+
+const filePathSeparator = os.PathSeparator
+
+type virtualFile struct {
+	mem.File
+
+	Callback func(file document.File) error
+}
+
+// Override close behavior.
+// When the file handle is closed, we will forward the file content via callback.
+func (v *virtualFile) Close() error {
+	if v.Callback != nil {
+		file := document.File{
+			Name: v.Name(),
+		}
+
+		var err error
+		if file.Data, err = io.ReadAll(mem.NewReadOnlyFileHandle(v.Data())); err != nil {
+			v.File.Close()
+			return err
+		}
+
+		if err := v.Callback(file); err != nil {
+			v.File.Close()
+			return err
+		}
+	}
+
+	return v.File.Close()
+}
+
+var _ afero.File = &virtualFile{}
+
+type virtualFS struct {
+	Callback func(file document.File) error
+}
+
+var _ afero.Fs = &virtualFS{}
+
+// Create creates a file in the filesystem, returning the file and an error, if any happens.
+func (v *virtualFS) Create(name string) (afero.File, error) {
+	name = normalizePath(name)
+	//log.Printf("VirtualFS: Create: %v", name)
+	file := mem.CreateFile(name)
+	fileHandle := *mem.NewFileHandle(file)
+	return &virtualFile{File: fileHandle, Callback: v.Callback}, nil
+}
+
+// Mkdir creates a directory in the filesystem, return an error if any happens.
+func (v *virtualFS) Mkdir(name string, perm os.FileMode) error {
+	//name = normalizePath(name)
+	//log.Printf("VirtualFS: Mkdir: %v, %v", name, perm)
+	return nil
+}
+
+// MkdirAll creates a directory path and all parents that does not exist yet.
+func (v *virtualFS) MkdirAll(path string, perm os.FileMode) error {
+	//path = normalizePath(path)
+	//log.Printf("VirtualFS: MkdirAll: %v, %v", path, perm)
+	return nil
+}
+
+// Open opens a file, returning it or an error, if any happens.
+func (v *virtualFS) Open(name string) (afero.File, error) {
+	name = normalizePath(name)
+	//log.Printf("VirtualFS: Open: %v", name)
+	dir := mem.CreateDir(name)
+	mem.SetMode(dir, os.ModeDir|0o755)
+	return mem.NewReadOnlyFileHandle(dir), nil
+}
+
+// OpenFile opens a file using the given flags and the given mode.
+func (v *virtualFS) OpenFile(name string, flag int, perm os.FileMode) (afero.File, error) {
+	name = normalizePath(name)
+	//log.Printf("VirtualFS: OpenFile: %v, %v, %v", name, flag, perm)
+	return v.Create(name)
+}
+
+// Remove removes a file identified by name, returning an error, if any happens.
+func (v *virtualFS) Remove(name string) error {
+	name = normalizePath(name)
+	//log.Printf("VirtualFS: Remove: %v", name)
+	return &os.PathError{Op: "remove", Path: name, Err: os.ErrNotExist}
+}
+
+// RemoveAll removes a directory path and any children it contains. It does not fail if the path does not exist (return nil).
+func (v *virtualFS) RemoveAll(path string) error {
+	//path = normalizePath(path)
+	//log.Printf("VirtualFS: RemoveAll: %v", path)
+	return nil
+}
+
+// Rename renames a file.
+func (v *virtualFS) Rename(oldName, newName string) error {
+	oldName = normalizePath(oldName)
+	//newName = normalizePath(newName)
+	//log.Printf("VirtualFS: Rename: %v -> %v", oldName, newName)
+	return &os.PathError{Op: "rename", Path: oldName, Err: os.ErrNotExist}
+}
+
+// Stat returns a FileInfo describing the named file, or an error, if any happens.
+func (v *virtualFS) Stat(name string) (os.FileInfo, error) {
+	name = normalizePath(name)
+	//log.Printf("VirtualFS: Stat: %v", name)
+	dir := mem.CreateDir(name)
+	mem.SetMode(dir, os.ModeDir|0o755)
+	return mem.GetFileInfo(dir), nil
+}
+
+// The name of this FileSystem.
+func (v *virtualFS) Name() string {
+	return "ScanyoneroVirtualFS"
+}
+
+// Chmod changes the mode of the named file to mode.
+func (v *virtualFS) Chmod(name string, mode os.FileMode) error {
+	name = normalizePath(name)
+	//log.Printf("VirtualFS: Chmod: %v, %v", name, mode)
+	return &os.PathError{Op: "chmod", Path: name, Err: os.ErrNotExist}
+}
+
+// Chown changes the uid and gid of the named file.
+func (v *virtualFS) Chown(name string, uid, gid int) error {
+	name = normalizePath(name)
+	//log.Printf("VirtualFS: Chown: %v, %v, %v", name, uid, gid)
+	return &os.PathError{Op: "chown", Path: name, Err: os.ErrNotExist}
+}
+
+// Chtimes changes the access and modification times of the named file.
+func (v *virtualFS) Chtimes(name string, atime time.Time, mtime time.Time) error {
+	name = normalizePath(name)
+	//log.Printf("VirtualFS: Chtimes: %v, %v, %v", name, atime, mtime)
+	return &os.PathError{Op: "chtimes", Path: name, Err: os.ErrNotExist}
+}
--- a/go.mod
+++ b/go.mod
@ -1,3 +1,31 @@
-module ocrmypdf-runner
+module Scanyonero

-go 1.19
+go 1.23.0
+
+toolchain go1.24.2
+
+require (
+	github.com/chai2010/tiff v0.0.0-20211005095045-4ec2aa243943
+	github.com/fclairamb/ftpserverlib v0.25.0
+	github.com/gorilla/websocket v1.5.3
+	github.com/nfnt/resize v0.0.0-20180221191011-83c6a9932646
+	github.com/pdfcpu/pdfcpu v0.10.2
+	github.com/spf13/afero v1.14.0
+	neilpa.me/go-jfif v0.5.0
+)
+
+require (
+	github.com/fclairamb/go-log v0.5.0 // indirect
+	github.com/hhrutter/lzw v1.0.0 // indirect
+	github.com/hhrutter/pkcs7 v0.2.0 // indirect
+	github.com/hhrutter/tiff v1.0.2 // indirect
+	github.com/mattn/go-runewidth v0.0.16 // indirect
+	github.com/pkg/errors v0.9.1 // indirect
+	github.com/rivo/uniseg v0.4.7 // indirect
+	golang.org/x/crypto v0.37.0 // indirect
+	golang.org/x/image v0.26.0 // indirect
+	golang.org/x/sys v0.32.0 // indirect
+	golang.org/x/text v0.24.0 // indirect
+	gopkg.in/yaml.v2 v2.4.0 // indirect
+	neilpa.me/go-x v0.2.0 // indirect
+)
--- a/go.sum
+++ b/go.sum
@ -0,0 +1,57 @@
+github.com/chai2010/tiff v0.0.0-20211005095045-4ec2aa243943 h1:CjuhVIUiyWQZVY4rmcvm/9R+60e/Wi6LkXyHU38MqXI=
+github.com/chai2010/tiff v0.0.0-20211005095045-4ec2aa243943/go.mod h1:FhMMqekobM33oGdTfbi65oQ9P7bnQ5/0EDfmleW35RE=
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/fclairamb/ftpserverlib v0.25.0 h1:swV2CK+WiN9KEkqkwNgGbSIfRoYDWNno41hoVtYwgfA=
+github.com/fclairamb/ftpserverlib v0.25.0/go.mod h1:LIDqyiFPhjE9IuzTkntST8Sn8TaU6NRgzSvbMpdfRC4=
+github.com/fclairamb/go-log v0.5.0 h1:Gz9wSamEaA6lta4IU2cjJc2xSq5sV5VYSB5w/SUHhVc=
+github.com/fclairamb/go-log v0.5.0/go.mod h1:XoRO1dYezpsGmLLkZE9I+sHqpqY65p8JA+Vqblb7k40=
+github.com/go-kit/log v0.2.1 h1:MRVx0/zhvdseW+Gza6N9rVzU/IVzaeE1SFI4raAhmBU=
+github.com/go-kit/log v0.2.1/go.mod h1:NwTd00d/i8cPZ3xOwwiv2PO5MOcx78fFErGNcVmBjv0=
+github.com/go-logfmt/logfmt v0.5.1 h1:otpy5pqBCBZ1ng9RQ0dPu4PN7ba75Y/aA+UpowDyNVA=
+github.com/go-logfmt/logfmt v0.5.1/go.mod h1:WYhtIu8zTZfxdn5+rREduYbwxfcBr/Vr6KEVveWlfTs=
+github.com/gorilla/websocket v1.5.3 h1:saDtZ6Pbx/0u+bgYQ3q96pZgCzfhKXGPqt7kZ72aNNg=
+github.com/gorilla/websocket v1.5.3/go.mod h1:YR8l580nyteQvAITg2hZ9XVh4b55+EU/adAjf1fMHhE=
+github.com/hhrutter/lzw v1.0.0 h1:laL89Llp86W3rRs83LvKbwYRx6INE8gDn0XNb1oXtm0=
+github.com/hhrutter/lzw v1.0.0/go.mod h1:2HC6DJSn/n6iAZfgM3Pg+cP1KxeWc3ezG8bBqW5+WEo=
+github.com/hhrutter/pkcs7 v0.2.0 h1:i4HN2XMbGQpZRnKBLsUwO3dSckzgX142TNqY/KfXg+I=
+github.com/hhrutter/pkcs7 v0.2.0/go.mod h1:aEzKz0+ZAlz7YaEMY47jDHL14hVWD6iXt0AgqgAvWgE=
+github.com/hhrutter/tiff v1.0.2 h1:7H3FQQpKu/i5WaSChoD1nnJbGx4MxU5TlNqqpxw55z8=
+github.com/hhrutter/tiff v1.0.2/go.mod h1:pcOeuK5loFUE7Y/WnzGw20YxUdnqjY1P0Jlcieb/cCw=
+github.com/mattn/go-runewidth v0.0.16 h1:E5ScNMtiwvlvB5paMFdw9p4kSQzbXFikJ5SQO6TULQc=
+github.com/mattn/go-runewidth v0.0.16/go.mod h1:Jdepj2loyihRzMpdS35Xk/zdY8IAYHsh153qUoGf23w=
+github.com/nfnt/resize v0.0.0-20180221191011-83c6a9932646 h1:zYyBkD/k9seD2A7fsi6Oo2LfFZAehjjQMERAvZLEDnQ=
+github.com/nfnt/resize v0.0.0-20180221191011-83c6a9932646/go.mod h1:jpp1/29i3P1S/RLdc7JQKbRpFeM1dOBd8T9ki5s+AY8=
+github.com/pdfcpu/pdfcpu v0.10.2 h1:DB2dWuoq0eF0QwHjgyLirYKLTCzFOoZdmmIUSu72aL0=
+github.com/pdfcpu/pdfcpu v0.10.2/go.mod h1:Q2Z3sqdRqHTdIq1mPAUl8nfAoim8p3c1ASOaQ10mCpE=
+github.com/pkg/errors v0.9.1 h1:FEBLx1zS214owpjy7qsBeixbURkuhQAwrK5UwLGTwt4=
+github.com/pkg/errors v0.9.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/rivo/uniseg v0.2.0/go.mod h1:J6wj4VEh+S6ZtnVlnTBMWIodfgj8LQOQFoIToxlJtxc=
+github.com/rivo/uniseg v0.4.7 h1:WUdvkW8uEhrYfLC4ZzdpI2ztxP1I582+49Oc5Mq64VQ=
+github.com/rivo/uniseg v0.4.7/go.mod h1:FN3SvrM+Zdj16jyLfmOkMNblXMcoc8DfTHruCPUcx88=
+github.com/secsy/goftp v0.0.0-20200609142545-aa2de14babf4 h1:PT+ElG/UUFMfqy5HrxJxNzj3QBOf7dZwupeVC+mG1Lo=
+github.com/secsy/goftp v0.0.0-20200609142545-aa2de14babf4/go.mod h1:MnkX001NG75g3p8bhFycnyIjeQoOjGL6CEIsdE/nKSY=
+github.com/spf13/afero v1.14.0 h1:9tH6MapGnn/j0eb0yIXiLjERO8RB6xIVZRDCX7PtqWA=
+github.com/spf13/afero v1.14.0/go.mod h1:acJQ8t0ohCGuMN3O+Pv0V0hgMxNYDlvdk+VTfyZmbYo=
+github.com/stretchr/testify v1.10.0 h1:Xv5erBjTwe/5IxqUQTdXv5kgmIvbHo3QQyRwhJsOfJA=
+github.com/stretchr/testify v1.10.0/go.mod h1:r2ic/lqez/lEtzL7wO/rwa5dbSLXVDPFyf8C91i36aY=
+golang.org/x/crypto v0.37.0 h1:kJNSjF/Xp7kU0iB2Z+9viTPMW4EqqsrywMXLJOOsXSE=
+golang.org/x/crypto v0.37.0/go.mod h1:vg+k43peMZ0pUMhYmVAWysMK35e6ioLh3wB8ZCAfbVc=
+golang.org/x/image v0.26.0 h1:4XjIFEZWQmCZi6Wv8BoxsDhRU3RVnLX04dToTDAEPlY=
+golang.org/x/image v0.26.0/go.mod h1:lcxbMFAovzpnJxzXS3nyL83K27tmqtKzIJpctK8YO5c=
+golang.org/x/sys v0.32.0 h1:s77OFDvIQeibCmezSnk/q6iAfkdiQaJi4VzroCFrN20=
+golang.org/x/sys v0.32.0/go.mod h1:BJP2sWEmIv4KK5OTEluFJCKSidICx8ciO85XgH3Ak8k=
+golang.org/x/text v0.24.0 h1:dd5Bzh4yt5KYA8f9CJHCP4FB4D51c2c6JvN37xJJkJ0=
+golang.org/x/text v0.24.0/go.mod h1:L8rBsPeo2pSS+xqN0d5u2ikmjtmoJbDBT1b7nHvFCdU=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v2 v2.4.0 h1:D8xgwECY7CYvx+Y2n4sBz93Jn9JRvxdiyyo8CTfuKaY=
+gopkg.in/yaml.v2 v2.4.0/go.mod h1:RDklbk79AGWmwhnvt/jBztapEOGDOx6ZbXqjP6csGnQ=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
+neilpa.me/go-jfif v0.5.0 h1:MNx8t0K4ysVKywCb5O98FhN3CcYih7rAUpCehj5HgtQ=
+neilpa.me/go-jfif v0.5.0/go.mod h1:EbYXM1sxsAfbRgty+I5j1Ommm6WTsLKT+KXNgC998d0=
+neilpa.me/go-x v0.2.0 h1:GbLRDtAZ9MgVrwrIe3jWnHF2W40LCFA9Ng/aDbd9GVs=
+neilpa.me/go-x v0.2.0/go.mod h1:aIemU+pQYLLV3dygXotHKF7SantXe5HzZR6VIjzY/4g=
--- a/init.go
+++ b/init.go
@ -1,6 +1,6 @@
 package main

-import (
+/*import (
 	"path/filepath"
 	"time"
 )
@ -12,4 +12,4 @@ func init() {
 		Interval:      5 * time.Second,
 	}
 	runner.Run()
-}
+}*/
--- a/jsconfig.json
+++ b/jsconfig.json
@ -0,0 +1,7 @@
+{
+    "compilerOptions": {
+        "alwaysStrict": true,
+        "checkJs": true,
+        "target": "ES6",
+    },
+}
--- a/main.go
+++ b/main.go
@ -1,12 +1,83 @@
 package main

-import "log"
+import (
+	"Scanyonero/document"
+	"Scanyonero/ftpserver"
+	"Scanyonero/unit"
+	"log"
+	"net/http"
+	"path/filepath"
+	"regexp"
+)

 func main() {
-	log.Printf("Starting OCRmyPDF-runner.")
+	log.Printf("Starting Scanyonero.")

-	// The runners will be started in some init.go file.
-
-	// Wait forever.
-	select {}
+	// Start FTP server.
+	ftpServer, err := ftpserver.NewFTPServer("", "", "127.0.0.1:21")
+	if err != nil {
+		log.Panicf("Failed to start FTP server: %v.", err)
+	}
+	defer ftpServer.Stop()
+
+	// Web and WS server.
+	server := NewServer()
+
+	// Add test documents.
+	server.Documents.Append(LoadExampleQueueEntries()...)
+	server.Documents.Append(LoadExampleQueueEntries()...)
+	server.Documents.Append(LoadExampleQueueEntries()...)
+	server.Documents.Append(LoadExampleQueueEntries()...)
+
+	go func() {
+		ingestor := document.Ingestor{
+			DefaultDPI: unit.PerInch(150),
+			Rules: []document.IngestorRule{{
+				Match: struct {
+					Name    *regexp.Regexp
+					XPixels *int
+					YPixels *int
+				}{
+					Name: regexp.MustCompile(`^.*\.pdf$`),
+				},
+				Action: struct {
+					MediumWidth  *unit.Millimeter
+					MediumHeight *unit.Millimeter
+					ScanOffsetX  *unit.Millimeter
+					ScanOffsetY  *unit.Millimeter
+				}{
+					MediumWidth: &([]unit.Millimeter{100}[0]),
+				},
+			}},
+		}
+
+		for file := range ftpServer.FileChan() {
+			docPages, err := ingestor.Ingest(file)
+			if err != nil {
+				log.Printf("Failed to ingest document file %q: %v.", file.Name, err)
+				continue
+			}
+
+			var entries []QueueEntry
+			for _, page := range docPages {
+				entries = append(entries, QueueEntry{
+					ID:             NewQueueEntryID(),
+					Name:           filepath.Base(file.Name),
+					QueueEntryData: QueueEntryDataPage{Page: &page},
+				})
+			}
+			entries = append(entries, QueueEntry{ID: NewQueueEntryID(), QueueEntryData: QueueEntryDataSeparator{}})
+
+			server.Documents.Lock()
+			server.Documents.Append(entries...)
+			server.Documents.Unlock()
+		}
+	}()
+
+	http.Handle("/", server)
+
+	log.Println("Server is running on port 8080.")
+	if err := http.ListenAndServe(":8080", nil); err != nil {
+		log.Panicf("ListenAndServe failed: %v.", err)
+	}
 }
--- a/ocrmypdf/cli-options.go
+++ b/ocrmypdf/cli-options.go
@ -0,0 +1,13 @@
+package ocrmypdf
+
+type CLIOptions struct {
+	Custom []string // Custom command line options go here.
+}
+
+// Args returns a list of CLI arguments that should be passed to the executable.
+func (c *CLIOptions) Args() (result []string) {
+
+	result = append(result, c.Custom...)
+
+	return
+}
--- a/ocrmypdf/cli.go
+++ b/ocrmypdf/cli.go
@ -0,0 +1,88 @@
+package ocrmypdf
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"os/exec"
+	"strings"
+)
+
+type CLI struct {
+	// The OCRmyPDF executable path can be overridden here. Otherwise the default path will be used.
+	// Special cases:
+	// - "py -m ocrmypdf": This will run "py -m ocrmypdf".
+	ExecutablePath string
+}
+
+// executableAndArgs returns the executable name and its base arguments.
+func (c CLI) executableAndArgs() (string, []string) {
+	// Get path of executable.
+	execPath := ExecutablePath
+	if c.ExecutablePath != "" {
+		execPath = c.ExecutablePath
+	}
+
+	// Special cases.
+	var args []string
+	switch execPath {
+	case "py -m ocrmypdf":
+		execPath, args = "py", []string{"-m", "ocrmypdf"}
+	}
+
+	return execPath, args
+}
+
+// VersionString returns the version string as returned by OCRmyPDF.
+func (c CLI) VersionString() (string, error) {
+	execPath, args := c.executableAndArgs()
+
+	args = append(args, "--version")
+
+	cmd := exec.Command(execPath, args...)
+
+	var output, errBuffer bytes.Buffer
+	cmd.Stdout = &output
+	cmd.Stderr = &errBuffer
+
+	if err := cmd.Run(); err != nil {
+		switch err := err.(type) {
+		case *exec.ExitError:
+			return "", fmt.Errorf("OCRmyPDF stopped with exit code %v: %v", err.ExitCode(), errBuffer.String())
+		default:
+			return "", err
+		}
+	}
+
+	return strings.TrimRight(output.String(), "\n\r"), nil
+}
+
+// Run takes a document from input, and writes the resulting document into output.
+// The options parameter is optional.
+func (c CLI) Run(input io.Reader, output io.Writer, options *CLIOptions) error {
+	execPath, args := c.executableAndArgs()
+
+	if options != nil {
+		args = append(args, options.Args()...)
+	}
+
+	args = append(args, "-", "-")
+
+	cmd := exec.Command(execPath, args...)
+	cmd.Stdin = input
+	cmd.Stdout = output
+
+	errBuffer := bytes.Buffer{}
+	cmd.Stderr = &errBuffer
+
+	if err := cmd.Run(); err != nil {
+		switch err := err.(type) {
+		case *exec.ExitError:
+			return fmt.Errorf("OCRmyPDF stopped with exit code %v: %v", err.ExitCode(), errBuffer.String())
+		default:
+			return err
+		}
+	}
+
+	return nil
+}
--- a/ocrmypdf/cli_test.go
+++ b/ocrmypdf/cli_test.go
@ -0,0 +1,40 @@
+package ocrmypdf_test
+
+import (
+	"Scanyonero/ocrmypdf"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestCLI_VersionString(t *testing.T) {
+	cli := ocrmypdf.CLI{}
+
+	v, err := cli.VersionString()
+	if err != nil {
+		t.Fatalf("VersionString() returned error: %v", err)
+	}
+	if v == "" {
+		t.Errorf("Returned version string is empty: %v", v)
+	}
+}
+
+func TestCLI_Run(t *testing.T) {
+	t.SkipNow()
+
+	cli := ocrmypdf.CLI{}
+
+	source, err := os.Open(filepath.Join(".", "..", "test-documents", "typst-example", "600 DPI Flatbed.pdf"))
+	if err != nil {
+		t.Fatalf("Couldn't open file: %v.", err)
+	}
+
+	dest, err := os.Create(filepath.Join(".", "Output.pdf"))
+	if err != nil {
+		t.Fatalf("Couldn't create file: %v.", err)
+	}
+
+	if err := cli.Run(source, dest, nil); err != nil {
+		t.Fatalf("Run() returned error: %v", err)
+	}
+}
--- a/ocrmypdf/cli_unix.go
+++ b/ocrmypdf/cli_unix.go
@ -0,0 +1,6 @@
+//go:build unix
+
+package ocrmypdf
+
+// The path to the OCRmyPDF executable.
+var ExecutablePath = "ocrmypdf"
--- a/ocrmypdf/cli_windows.go
+++ b/ocrmypdf/cli_windows.go
@ -0,0 +1,6 @@
+//go:build windows
+
+package ocrmypdf
+
+// The path to the OCRmyPDF executable.
+var ExecutablePath = "py -m ocrmypdf"
--- a/queue-entry-data-page.go
+++ b/queue-entry-data-page.go
@ -0,0 +1,11 @@
+package main
+
+import "Scanyonero/document"
+
+type QueueEntryDataPage struct {
+	Page *document.Page `json:"page"`
+}
+
+func (q QueueEntryDataPage) QueueEntryDataType() string {
+	return "Page"
+}
--- a/queue-entry-data-separator.go
+++ b/queue-entry-data-separator.go
@ -0,0 +1,7 @@
+package main
+
+type QueueEntryDataSeparator struct{}
+
+func (q QueueEntryDataSeparator) QueueEntryDataType() string {
+	return "Separator"
+}
--- a/queue-entry-data.go
+++ b/queue-entry-data.go
@ -0,0 +1,5 @@
+package main
+
+type QueueEntryData interface {
+	QueueEntryDataType() string
+}
--- a/queue-entry.go
+++ b/queue-entry.go
@ -0,0 +1,41 @@
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"sync/atomic"
+)
+
+var queueEntryIDCounter atomic.Uint32
+
+// NewQueueEntryID returns a unique document id.
+func NewQueueEntryID() QueueEntryID {
+	return QueueEntryID(queueEntryIDCounter.Add(1))
+}
+
+type QueueEntryID int
+
+// QueueEntry can contain a single or multiple scanned pages.
+type QueueEntry struct {
+	ID   QueueEntryID `json:"id"`
+	Name string       `json:"name"`
+
+	QueueEntryData
+}
+
+func (q QueueEntry) MarshalJSON() ([]byte, error) {
+	if q.QueueEntryData == nil {
+		return nil, fmt.Errorf("queue entry doesn't contain any data")
+	}
+
+	type embedded QueueEntry // Prevent recursion.
+	return json.Marshal(
+		struct {
+			embedded
+			Type string `json:"type"`
+		}{
+			embedded: embedded(q),
+			Type:     q.QueueEntryDataType(),
+		},
+	)
+}
--- a/queue.go
+++ b/queue.go
@ -0,0 +1,186 @@
+package main
+
+import (
+	"slices"
+	"sync"
+)
+
+// Queue contains a list of scanned documents.
+// A user can issue operations on these entries.
+//
+// The list is synced between the server and clients via websockets.
+type Queue struct {
+	sync.Mutex
+
+	Documents []QueueEntry
+
+	listeners map[chan<- ServerWebsocketPacket]struct{}
+}
+
+// RegisterListener will add the given channel c to receive updates in the form of websocket packets.
+//
+// UnregisterListener must be called before the channel can be closed or stopped reading from.
+func (d *Queue) RegisterListener(c chan<- ServerWebsocketPacket) {
+	d.Lock()
+	defer d.Unlock()
+
+	if d.listeners == nil {
+		d.listeners = make(map[chan<- ServerWebsocketPacket]struct{})
+	}
+
+	d.listeners[c] = struct{}{}
+
+	// Send current document queue.
+	c <- &ServerWebsocketPacketQueueReplace{Documents: d.Documents}
+}
+
+// UnregisterListener will stop the given listener from receiving updates.
+// Upon return, the listener will not receive any updates from the queue.
+func (d *Queue) UnregisterListener(c chan<- ServerWebsocketPacket) {
+	d.Lock()
+	defer d.Unlock()
+
+	if d.listeners == nil {
+		d.listeners = make(map[chan<- ServerWebsocketPacket]struct{})
+	}
+
+	delete(d.listeners, c)
+}
+
+// Broadcast will send a websocket packet to all registered listeners.
+//
+// The Queue must be locked when calling this.
+func (d *Queue) Broadcast(p ...ServerWebsocketPacket) {
+	for listener := range d.listeners {
+		for _, packet := range p {
+			listener <- packet
+		}
+	}
+}
+
+// DeleteAt removes all elements at [i:j].
+//
+// This will automatically limit the indices to valid ranges.
+//
+// The Queue must be locked when calling this.
+func (d *Queue) DeleteAt(i, j int) {
+	i = max(0, min(i, len(d.Documents)-1)) // Limit to [0; len).
+	j = max(0, min(j, len(d.Documents)))   // Limit to [0; len].
+	if i >= j {
+		return
+	}
+
+	d.Documents = slices.Delete(d.Documents, i, j)
+
+	d.Broadcast(&ServerWebsocketPacketQueueDeleteAt{IndexA: i, IndexB: j})
+}
+
+// Delete removes the elements with the given DocumentIDs.
+//
+// The Queue must be locked when calling this.
+func (d *Queue) Delete(ids ...QueueEntryID) {
+	for i, doc := range slices.Backward(d.Documents) {
+		if slices.Contains(ids, doc.ID) {
+			d.DeleteAt(i, i+1)
+		}
+	}
+}
+
+// InsertAt inserts the given document at index i.
+//
+// Documents will be shifted accordingly, valid indices are in the range of [0; len(queue)].
+// This will automatically limit the index to valid ranges.
+//
+// The Queue must be locked when calling this.
+func (d *Queue) InsertAt(i int, documents ...QueueEntry) {
+	i = max(0, min(i, len(d.Documents))) // Limit to [0; len].
+
+	d.Documents = slices.Insert(d.Documents, i, documents...)
+
+	d.Broadcast(&ServerWebsocketPacketQueueInsertAt{Index: i, Documents: documents})
+}
+
+// Append will add the given documents to the end of the queue.
+//
+// The Queue must be locked when calling this.
+func (d *Queue) Append(documents ...QueueEntry) {
+	d.InsertAt(len(d.Documents), documents...)
+}
+
+// Replace will replace the whole list of documents with the given one.
+//
+// The Queue must be locked when calling this.
+func (d *Queue) Replace(documents ...QueueEntry) {
+	d.Documents = slices.Clone(documents)
+
+	d.Broadcast(&ServerWebsocketPacketQueueReplace{Documents: documents})
+}
+
+// ShiftAt will move the element at index i by the given offset.
+//
+// This will automatically limit the index and the offset to valid ranges.
+//
+// The Queue must be locked when calling this.
+func (d *Queue) ShiftAt(i, offset int) {
+	if len(d.Documents) <= 0 {
+		return
+	}
+	i = max(0, min(i, len(d.Documents)-1))              // Limit to [0; len).
+	offset = max(-i, min(offset, len(d.Documents)-i-1)) // Limit to [-i; len-i-1].
+
+	for tempOffset, i := offset, i; tempOffset != 0; {
+		switch {
+		case tempOffset > 0:
+			d.Documents[i], d.Documents[i+1] = d.Documents[i+1], d.Documents[i]
+			tempOffset--
+			i++
+		case offset < 0:
+			d.Documents[i], d.Documents[i-1] = d.Documents[i-1], d.Documents[i]
+			tempOffset++
+			i--
+		}
+	}
+
+	d.Broadcast(&ServerWebsocketPacketQueueShiftAt{Index: i, Offset: offset})
+}
+
+// Shift will move the index of all elements with the given DocumentIDs by offset.
+//
+// The Queue must be locked when calling this.
+func (d *Queue) Shift(offset int, ids ...QueueEntryID) {
+	switch {
+	case offset < 0:
+		for i, entry := range d.Documents {
+			if slices.Contains(ids, entry.ID) {
+				if offset < -i {
+					offset = -i
+				}
+				d.ShiftAt(i, offset)
+			}
+		}
+
+	case offset > 0:
+		for i, entry := range slices.Backward(d.Documents) {
+			if slices.Contains(ids, entry.ID) {
+				if offset > len(d.Documents)-i-1 {
+					offset = len(d.Documents) - i - 1
+				}
+				d.ShiftAt(i, offset)
+			}
+		}
+	}
+}
+
+// QueueEntryByID returns the QueueEntry with the given ID.
+//
+// The Queue must be locked when calling this.
+func (d *Queue) QueueEntryByID(id QueueEntryID) *QueueEntry {
+	for i := range d.Documents {
+		document := &d.Documents[i]
+		if document.ID == id {
+			return document
+		}
+	}
+
+	return nil
+}
--- a/server-websocket-packet.go
+++ b/server-websocket-packet.go
@ -0,0 +1,12 @@
+package main
+
+// ServerWebsocketPacket represents a websocket packet.
+type ServerWebsocketPacket interface {
+	Type() string
+}
+
+var serverWebsocketPacketRegistry map[string]ServerWebsocketPacket = map[string]ServerWebsocketPacket{}
+
+func ServerWebsocketPacketRegister(prototype ServerWebsocketPacket) {
+	serverWebsocketPacketRegistry[prototype.Type()] = prototype
+}
--- a/server-websocket-packets.go
+++ b/server-websocket-packets.go
@ -0,0 +1,70 @@
+package main
+
+// ServerWebsocketPacketQueueDeleteAt represents a delete operation on a document queue list.
+// The range of the deleted indices is [IndexA; IndexB).
+type ServerWebsocketPacketQueueDeleteAt struct {
+	IndexA int `json:"indexA"` // Starting index of the deletion range.
+	IndexB int `json:"indexB"` // End index of the deletion range. This index is not included in the range.
+}
+
+func (s *ServerWebsocketPacketQueueDeleteAt) Type() string { return "QueueDeleteAt" }
+
+func init() { ServerWebsocketPacketRegister(&ServerWebsocketPacketQueueDeleteAt{}) }
+
+// ServerWebsocketPacketQueueDelete represents a delete operation on a document queue list.
+type ServerWebsocketPacketQueueDelete struct {
+	IDs []QueueEntryID `json:"ids"` // IDs of the documents.
+}
+
+func (s *ServerWebsocketPacketQueueDelete) Type() string { return "QueueDelete" }
+
+func init() { ServerWebsocketPacketRegister(&ServerWebsocketPacketQueueDelete{}) }
+
+// ServerWebsocketPacketQueueInsertAt represents an insert operation on a document queue list.
+type ServerWebsocketPacketQueueInsertAt struct {
+	Index     int          `json:"index"`
+	Documents []QueueEntry `json:"documents"`
+}
+
+func (s *ServerWebsocketPacketQueueInsertAt) Type() string { return "QueueInsertAt" }
+
+func init() { ServerWebsocketPacketRegister(&ServerWebsocketPacketQueueInsertAt{}) }
+
+// ServerWebsocketPacketQueueReplace represents a replace operation on a document queue list.
+type ServerWebsocketPacketQueueReplace struct {
+	Documents []QueueEntry `json:"documents"`
+}
+
+func (s *ServerWebsocketPacketQueueReplace) Type() string { return "QueueReplace" }
+
+func init() { ServerWebsocketPacketRegister(&ServerWebsocketPacketQueueReplace{}) }
+
+// ServerWebsocketPacketQueueShiftAt represents a shift operation on a document queue list.
+type ServerWebsocketPacketQueueShiftAt struct {
+	Index  int `json:"index"`  // Index of the to be shifted element.
+	Offset int `json:"offset"` // Shift offset.
+}
+
+func (s *ServerWebsocketPacketQueueShiftAt) Type() string { return "QueueShiftAt" }
+
+func init() { ServerWebsocketPacketRegister(&ServerWebsocketPacketQueueShiftAt{}) }
+
+// ServerWebsocketPacketQueueShift represents a shift operation on a document queue list.
+type ServerWebsocketPacketQueueShift struct {
+	IDs    []QueueEntryID `json:"ids"`    // IDs of the documents.
+	Offset int            `json:"offset"` // Shift offset.
+}
+
+func (s *ServerWebsocketPacketQueueShift) Type() string { return "QueueShift" }
+
+func init() { ServerWebsocketPacketRegister(&ServerWebsocketPacketQueueShift{}) }
+
+// ServerWebsocketPacketQueueUpdate represents an update operation of documents in a queue list.
+// The receiver should update any of the received documents in their local queue list.
+type ServerWebsocketPacketQueueUpdate struct {
+	Documents []QueueEntry `json:"documents"`
+}
+
+func (s *ServerWebsocketPacketQueueUpdate) Type() string { return "QueueUpdate" }
+
+func init() { ServerWebsocketPacketRegister(&ServerWebsocketPacketQueueUpdate{}) }
--- a/server-websocket.go
+++ b/server-websocket.go
@ -0,0 +1,101 @@
+package main
+
+import (
+	"encoding/json"
+	"log"
+	"net/http"
+
+	"github.com/gorilla/websocket"
+)
+
+var upgrader = websocket.Upgrader{}
+
+func (s *Server) handleWebSocket(w http.ResponseWriter, r *http.Request) {
+	conn, err := upgrader.Upgrade(w, r, nil)
+	if err != nil {
+		log.Printf("Upgrading connection to WS failed: %v.", err)
+		return
+	}
+	defer conn.Close()
+
+	sendChan := make(chan ServerWebsocketPacket)
+	defer close(sendChan)
+
+	// Goroutine for sending packets.
+	go func(sendChan <-chan ServerWebsocketPacket) {
+		for packet := range sendChan {
+			message := struct {
+				Type    string `json:"type"`
+				Payload any    `json:"payload"`
+			}{
+				Type:    packet.Type(),
+				Payload: packet,
+			}
+
+			messageData, err := json.Marshal(message)
+			if err != nil {
+				log.Printf("Failed to marshal websocket packet: %v.", err)
+				continue
+			}
+
+			conn.WriteMessage(websocket.TextMessage, messageData)
+		}
+	}(sendChan)
+
+	// Register listener on document queue updates.
+	s.Documents.RegisterListener(sendChan)
+	defer s.Documents.UnregisterListener(sendChan)
+
+	// Main loop that receives packets.
+	for {
+		messageType, data, err := conn.ReadMessage()
+		if err != nil {
+			log.Printf("Reading WS message failed: %v.", err)
+			break
+		}
+
+		switch messageType {
+		case websocket.CloseMessage:
+			log.Printf("Connection %v closed.", conn.LocalAddr())
+			return
+
+		case websocket.TextMessage:
+			//log.Printf("Message from %v: %s.", conn.LocalAddr(), data)
+
+			var message struct {
+				Type    string          `json:"type"`
+				Payload json.RawMessage `json:"payload"`
+			}
+
+			if err := json.Unmarshal(data, &message); err != nil {
+				log.Printf("Failed to marshal websocket packet from client %v: %v.", conn.LocalAddr(), err)
+				return
+			}
+
+			prototype, ok := serverWebsocketPacketRegistry[message.Type]
+			if !ok {
+				log.Printf("Unknown websocket packet type %q from client %v.", message.Type, conn.LocalAddr())
+				return
+			}
+
+			if err := json.Unmarshal(message.Payload, prototype); err != nil {
+				log.Printf("Failed to marshal websocket packet payload from client %v: %v.", conn.LocalAddr(), err)
+				return
+			}
+
+			switch packet := prototype.(type) {
+			case *ServerWebsocketPacketQueueDelete:
+				s.Documents.Lock()
+				s.Documents.Delete(packet.IDs...)
+				s.Documents.Unlock()
+			case *ServerWebsocketPacketQueueShift:
+				s.Documents.Lock()
+				s.Documents.Shift(packet.Offset, packet.IDs...)
+				s.Documents.Unlock()
+			default:
+				log.Printf("Websocket client %q sent unsupported packet type %T.", conn.LocalAddr(), prototype)
+				return
+			}
+		}
+	}
+}
--- a/server.go
+++ b/server.go
@ -0,0 +1,151 @@
+package main
+
+import (
+	"fmt"
+	"image/jpeg"
+	"log"
+	"net/http"
+	"strconv"
+
+	"github.com/nfnt/resize"
+)
+
+type Server struct {
+	http.ServeMux
+
+	Documents Queue
+}
+
+func NewServer() *Server {
+	s := &Server{}
+
+	s.Handle("/", http.FileServer(http.Dir("./static")))
+	s.HandleFunc("GET /api/queue-entry-page/{id}/image", s.handleGetQueueEntryImage)
+	s.HandleFunc("GET /api/queue-entry-page/{id}/preview", s.handleGetQueueEntryPreview)
+	//s.HandleFunc("PUT /documents/{id}", addItem)
+	//s.HandleFunc("DELETE /documents/{id}", s.handleRemoveDocument)
+	s.HandleFunc("/ws", s.handleWebSocket)
+
+	return s
+}
+
+func (s *Server) handleGetQueueEntryImage(w http.ResponseWriter, r *http.Request) {
+	var id QueueEntryID
+	if i, err := strconv.ParseInt(r.PathValue("id"), 10, 0); err != nil {
+		w.WriteHeader(http.StatusBadRequest)
+		msg := fmt.Sprintf("Failed to parse document id: %v.", err)
+		w.Write([]byte(msg))
+		log.Print(msg)
+		return
+	} else {
+		id = QueueEntryID(i)
+	}
+
+	s.Documents.Lock()
+	defer s.Documents.Unlock()
+
+	entry := s.Documents.QueueEntryByID(id)
+	if entry == nil {
+		w.WriteHeader(http.StatusNotFound)
+		msg := fmt.Sprintf("Failed to find %T with ID %v.", entry, id)
+		w.Write([]byte(msg))
+		log.Print(msg)
+		return
+	}
+
+	page, ok := entry.QueueEntryData.(QueueEntryDataPage)
+	if !ok {
+		w.WriteHeader(http.StatusInternalServerError)
+		msg := fmt.Sprintf("Entry %d isn't a page.", entry.ID)
+		w.Write([]byte(msg))
+		log.Print(msg)
+		return
+	}
+
+	if page.Page == nil {
+		w.WriteHeader(http.StatusInternalServerError)
+		msg := fmt.Sprintf("Entry %d doesn't contain any page data.", entry.ID)
+		w.Write([]byte(msg))
+		log.Print(msg)
+		return
+	}
+
+	if page.Page.Image == nil {
+		w.WriteHeader(http.StatusInternalServerError)
+		msg := fmt.Sprintf("Page %d doesn't contain any image.", entry.ID)
+		w.Write([]byte(msg))
+		log.Print(msg)
+		return
+	}
+
+	w.Header().Set("Content-Type", "image/jpeg")
+	if err := jpeg.Encode(w, page.Page.Image, nil); err != nil {
+		w.WriteHeader(http.StatusInternalServerError)
+		msg := fmt.Sprintf("Failed to encode JPEG: %v.", err)
+		w.Write([]byte(msg))
+		log.Print(msg)
+		return
+	}
+}
+
+func (s *Server) handleGetQueueEntryPreview(w http.ResponseWriter, r *http.Request) {
+	var id QueueEntryID
+	if i, err := strconv.ParseInt(r.PathValue("id"), 10, 0); err != nil {
+		w.WriteHeader(http.StatusBadRequest)
+		msg := fmt.Sprintf("Failed to parse document id: %v.", err)
+		w.Write([]byte(msg))
+		log.Print(msg)
+		return
+	} else {
+		id = QueueEntryID(i)
+	}
+
+	s.Documents.Lock()
+	defer s.Documents.Unlock()
+
+	entry := s.Documents.QueueEntryByID(id)
+	if entry == nil {
+		w.WriteHeader(http.StatusNotFound)
+		msg := fmt.Sprintf("Failed to find %T with ID %v.", entry, id)
+		w.Write([]byte(msg))
+		log.Print(msg)
+		return
+	}
+
+	page, ok := entry.QueueEntryData.(QueueEntryDataPage)
+	if !ok {
+		w.WriteHeader(http.StatusInternalServerError)
+		msg := fmt.Sprintf("Entry %d isn't a page.", entry.ID)
+		w.Write([]byte(msg))
+		log.Print(msg)
+		return
+	}
+
+	if page.Page == nil {
+		w.WriteHeader(http.StatusInternalServerError)
+		msg := fmt.Sprintf("Entry %d doesn't contain any page data.", entry.ID)
+		w.Write([]byte(msg))
+		log.Print(msg)
+		return
+	}
+
+	if page.Page.Image == nil {
+		w.WriteHeader(http.StatusInternalServerError)
+		msg := fmt.Sprintf("Page %d doesn't contain any image.", entry.ID)
+		w.Write([]byte(msg))
+		log.Print(msg)
+		return
+	}
+
+	// Resize image to a preview with a width of about 512 pixels.
+	img := resize.Resize(512, 0, page.Page.Image, resize.Lanczos2)
+
+	w.Header().Set("Content-Type", "image/jpeg")
+	if err := jpeg.Encode(w, img, nil); err != nil {
+		w.WriteHeader(http.StatusInternalServerError)
+		msg := fmt.Sprintf("Failed to encode JPEG: %v.", err)
+		w.Write([]byte(msg))
+		log.Print(msg)
+		return
+	}
+}
--- a/service/linux/systemd/ocrmypdf-runner.service
+++ b/service/linux/systemd/ocrmypdf-runner.service
@ -1,13 +0,0 @@
-[Unit]
-Description=A runner that will watch directories and runs OCRmyPDF on files in them.
-
-[Service]
-Restart=on-failure
-RestartSec=60s
-WorkingDirectory=/home/paperless/ocrmypdf-runner/
-ExecStart=go run .
-User=paperless
-Group=paperless
-
-[Install]
-WantedBy=multi-user.target
--- a/service/linux/systemd/scanyonero.service
+++ b/service/linux/systemd/scanyonero.service
@ -0,0 +1,10 @@
+[Unit]
+Description=A server that will receive scanned documents via FTP, process them and send them to paperless.
+
+[Service]
+Restart=on-failure
+RestartSec=60s
+ExecStart=go run .
+
+[Install]
+WantedBy=multi-user.target
--- a/static/index.html
+++ b/static/index.html
@ -0,0 +1,25 @@
+<!DOCTYPE html>
+<html lang="en">
+
+<head>
+	<meta charset="UTF-8">
+	<meta name="viewport" content="width=device-width, initial-scale=1.0">
+	<title>Scanyonero</title>
+	<link rel="stylesheet" href="styles.css">
+	<script type="module" src="./js/components/document-menu.js"></script>
+	<script type="module" src="./js/components/document-queue.js"></script>
+</head>
+
+<body>
+	<div id="main-container">
+		<document-menu id="document-menu"></document-menu>
+		<document-queue id="document-queue"></document-queue>
+	</div>
+
+	<script type="module">
+		import { App } from "./js/app.js";
+		const app = new App();
+	</script>
+</body>
+
+</html>
--- a/static/js/api.js
+++ b/static/js/api.js
@ -0,0 +1,128 @@
+export class API extends EventTarget {
+
+	constructor() {
+		super();
+
+		this.#socketOpen();
+	}
+
+	/** @type {WebSocket} */
+	#socket;
+
+	/**
+	 * Opens a new websocket connection, and adds all necessary listeners.
+	 */
+	#socketOpen() {
+		this.#socket = new WebSocket("ws://" + location.host + "/ws");
+
+		this.#socket.onopen = event => {
+			console.log(`Websocket connection opened.`)
+		}
+
+		this.#socket.onmessage = event => {
+			/** @type {{type: string, payload: any}} */
+			const data = JSON.parse(event.data);
+
+			switch (data.type) {
+				case "QueueDeleteAt": {
+					/** @type {CustomEventInit<import("./model").APIPacketQueueDeleteAt>} */
+					const eventData = { detail: data.payload };
+					this.dispatchEvent(new CustomEvent("queuedeleteat", eventData));
+					break;
+				}
+				case "QueueInsertAt": {
+					/** @type {CustomEventInit<import("./model").APIPacketQueueInsertAt>} */
+					const eventData = { detail: data.payload };
+					this.dispatchEvent(new CustomEvent("queueinsertat", eventData));
+					break;
+				}
+				case "QueueReplace": {
+					/** @type {CustomEventInit<import("./model").APIPacketQueueReplace>} */
+					const eventData = { detail: data.payload };
+					this.dispatchEvent(new CustomEvent("queuereplace", eventData));
+					break;
+				}
+				case "QueueShiftAt": {
+					/** @type {CustomEventInit<import("./model").APIPacketQueueShift>} */
+					const eventData = { detail: data.payload };
+					this.dispatchEvent(new CustomEvent("queueshiftat", eventData));
+					break;
+				}
+				default:
+					console.error(`Unknown websocket data type "${data.type}"`);
+					break;
+			}
+		}
+
+		this.#socket.onclose = event => {
+			console.log(`Socket is closed. Reconnect will be attempted in 1 second. Code: ${event.code} Reason: ${event.reason} WasClean: ${event.wasClean}.`);
+			setTimeout(() => {
+				this.#socketOpen();
+			}, 1000);
+		};
+
+		this.#socket.onerror = event => {
+			console.error(`Socket encountered error: ${event}. Closing socket.`);
+			this.#socket.close();
+		};
+	}
+
+	/**
+	 * Sends a document queue delete request to the server.
+	 * @param {...number} ids Document ids.
+	 */
+	queueDelete(...ids) {
+		if (this.#socket.readyState !== WebSocket.OPEN) {
+			return
+		}
+
+		/** @type {{type: string, payload: import("./model").APIPacketQueueDelete}} */
+		const message = { type: "QueueDelete", payload: { ids: ids } };
+		this.#socket.send(JSON.stringify(message));
+	}
+
+	/**
+	 * Sends a document queue shift request to the server.
+	 * @param {number} offset
+	 * @param {...number} ids Document ids.
+	 */
+	queueShift(offset, ...ids) {
+		if (this.#socket.readyState !== WebSocket.OPEN) {
+			return
+		}
+
+		/** @type {{type: string, payload: import("./model").APIPacketQueueShift}} */
+		const message = { type: "QueueShift", payload: { offset: offset, ids: ids } };
+		this.#socket.send(JSON.stringify(message));
+	}
+
+	/**
+	 * 
+	 * @param {"GET"|"POST"|"DELETE"|"UPDATE"} method 
+	 * @param {string} url 
+	 */
+	#ajaxRequest(method, url) {
+		return new Promise(function (resolve, reject) {
+			const xhr = new XMLHttpRequest();
+			xhr.open(method, url);
+			xhr.onload = function () {
+				if (this.status >= 200 && this.status < 300) {
+					resolve(this.response);
+				} else {
+					reject({
+						status: this.status,
+						statusText: this.statusText,
+					});
+				}
+			};
+			xhr.onerror = function () {
+				reject({
+					status: this.status,
+					statusText: this.statusText,
+				});
+			};
+			xhr.send();
+		});
+	}
+
+}
--- a/static/js/app.js
+++ b/static/js/app.js
@ -0,0 +1,25 @@
+import { API } from './api.js';
+import { DocumentMenu } from './components/document-menu.js';
+import { DocumentQueue } from './components/document-queue.js';
+
+export class App {
+	/** @type {API} */
+	#api;
+
+	/** @type {DocumentMenu} */
+	#documentMenu;
+
+	/** @type {DocumentQueue} */
+	#documentQueue;
+
+	constructor() {
+		this.#api = new API();
+
+		this.#documentMenu = document.querySelector("#document-menu");
+		this.#documentQueue = document.querySelector("#document-queue");
+
+		this.#documentMenu.documentQueue = this.#documentQueue;
+		this.#documentMenu.api = this.#api;
+		this.#documentQueue.api = this.#api;
+	}
+}
--- a/static/js/components/document-menu.js
+++ b/static/js/components/document-menu.js
@ -0,0 +1,126 @@
+import { API } from '../api.js';
+import { LitElement, css, html } from '../vendor/lit-html/lit-all.min.js';
+import { DocumentQueue } from './document-queue.js';
+
+export class DocumentMenu extends LitElement {
+	static properties = {
+		selectionAll: { type: Boolean },
+		selectionIndeterminate: { type: Boolean },
+	};
+
+	/** @type {API} */
+	api;
+
+	/** @type {DocumentQueue|undefined} */
+	#documentQueue;
+
+	/**
+	 * @param {DocumentQueue} documentQueue
+	 */
+	set documentQueue(documentQueue) {
+		this.#documentQueue = documentQueue;
+
+		this.#documentQueue.addEventListener("changeselection", /** @param {import('./document-queue.js').DocumentQueueEventChangeSelection} event */(event) => {
+			switch (event.detail.selectedIDs.length) {
+				case 0:
+					this.selectionAll = false; this.selectionIndeterminate = false;
+					break;
+
+				case event.detail.allIDs.length:
+					this.selectionAll = true; this.selectionIndeterminate = false;
+					break;
+
+				default:
+					this.selectionAll = false; this.selectionIndeterminate = true;
+					break;
+			}
+		});
+	}
+
+	constructor() {
+		super();
+		this.selectionAll = false;
+		this.selectionIndeterminate = false;
+	}
+
+	onCheckboxChange(event) {
+		switch (event.target.checked) {
+			case true:
+				this.selectionAll = true; this.selectionIndeterminate = false;
+				this.#documentQueue.selectAll(true);
+				break;
+
+			default:
+				this.selectionAll = false; this.selectionIndeterminate = false;
+				this.#documentQueue.selectAll(false);
+				break;
+		}
+	}
+
+	static styles = css`
+		:host {
+			display: flex;
+			padding: 8px;
+
+			background-color: black;
+		}
+
+		#select-all {
+			align-self: center;
+			margin-left: 8px;
+			margin-right: 16px;
+			width: 24px;
+			height: 24px;
+		}
+
+		#buttons {
+			display: flex;
+			flex-direction: row;
+			flex-wrap: wrap;
+			gap: 16px;
+		}
+
+		button {
+			padding: 8px;
+		}
+	`;
+
+	// @ts-ignore
+	render() {
+		return html`
+			<input id="select-all" type="checkbox" .checked=${this.selectionAll} .indeterminate=${this.selectionIndeterminate} @change=${this.onCheckboxChange}></input>
+			<div id="buttons">
+				<button @click=${this.onButtonUpwards} title="Shifts all selected elements upwards.">▲</button>
+				<button @click=${this.onButtonDownwards} title="Shifts all selected elements downwards.">▼</button>
+				<button title="Takes two stacks of single sided scans and merges them as if they were scanned from both sides.">Duplex Merge</button>
+				<button @click=${this.onButtonDelete}>Delete</button>
+			</div>
+		`;
+	}
+
+	/** @param {Event} event */
+	onButtonUpwards(event) {
+		if (this.api == undefined || this.#documentQueue == undefined) { return }
+
+		const sInfo = this.#documentQueue.selectionInfo();
+		this.api.queueShift(-1, ...sInfo.selectedIDs);
+	}
+
+	/** @param {Event} event */
+	onButtonDownwards(event) {
+		if (this.api == undefined || this.#documentQueue == undefined) { return }
+
+		const sInfo = this.#documentQueue.selectionInfo();
+		this.api.queueShift(1, ...sInfo.selectedIDs);
+	}
+
+	/** @param {Event} event */
+	onButtonDelete(event) {
+		if (this.api == undefined || this.#documentQueue == undefined) { return }
+
+		const sInfo = this.#documentQueue.selectionInfo();
+		this.api.queueDelete(...sInfo.selectedIDs);
+	}
+}
+
+customElements.define("document-menu", DocumentMenu);
--- a/static/js/components/document-queue-entry-page.js
+++ b/static/js/components/document-queue-entry-page.js
@ -0,0 +1,35 @@
+import { API } from '../api.js';
+import { LitElement, css, html, repeat } from '../vendor/lit-html/lit-all.min.js';
+
+export class DocumentQueueEntryPage extends LitElement {
+	static properties = {
+		queueEntry: { type: Object },
+
+		api: { type: Object, state: true },
+	};
+
+	constructor() {
+		super();
+
+		/** @type {API} */
+		this.api;
+		/** @type {import('model').APIQueueEntry} */
+		this.document;
+	}
+
+	static styles = css`
+		img {
+			width: 128px;
+		}
+	`;
+
+	// @ts-ignore
+	render() {
+		return html`
+			<img id="image" src=${`/api/queue-entry-page/${this.document.id}/preview`}></img>
+			<span>This is a document</span>
+		`;
+	}
+}
+
+customElements.define("document-queue-entry-page", DocumentQueueEntryPage);
--- a/static/js/components/document-queue-entry-separator.js
+++ b/static/js/components/document-queue-entry-separator.js
@ -0,0 +1,35 @@
+import { API } from '../api.js';
+import { LitElement, css, html, repeat } from '../vendor/lit-html/lit-all.min.js';
+
+export class DocumentQueueEntrySeparator extends LitElement {
+	static properties = {
+		queueEntry: { type: Object },
+
+		api: { type: Object, state: true },
+	};
+
+	constructor() {
+		super();
+
+		/** @type {API} */
+		this.api;
+		/** @type {import('model').APIQueueEntry} */
+		this.document;
+	}
+
+	static styles = css`
+		:host {
+			width: 100%;
+			background: black;
+		}
+	`;
+
+	// @ts-ignore
+	render() {
+		return html`
+			
+		`;
+	}
+}
+
+customElements.define("document-queue-entry-separator", DocumentQueueEntrySeparator);
--- a/static/js/components/document-queue-entry.js
+++ b/static/js/components/document-queue-entry.js
@ -0,0 +1,126 @@
+import { API } from '../api.js';
+import { LitElement, css, html, repeat } from '../vendor/lit-html/lit-all.min.js';
+import './document-queue-entry-page.js';
+import './document-queue-entry-separator.js';
+
+/** @typedef {{selected: boolean}} DocumentQueueEntryEventChangeSelectionDetails */
+/** @typedef {CustomEvent<DocumentQueueEntryEventChangeSelectionDetails>} DocumentQueueEntryEventChangeSelection */
+
+export class DocumentQueueEntry extends LitElement {
+	static properties = {
+		selected: { type: Boolean },
+		queueEntry: { type: Object },
+
+		api: { type: Object, state: true },
+	};
+
+	constructor() {
+		super();
+
+		this.selected = false;
+		/** @type {API} */
+		this.api;
+		/** @type {import('model').APIQueueEntry} */
+		this.queueEntry;
+	}
+
+	static styles = css`
+		:host {
+			padding: 8px;
+			display: flex;
+			flex-direction: row;
+			gap: 8px;
+			background-color: rgba(0, 0, 0, 0.1);
+			border-radius: 8px;
+		}
+
+		#left-bar {
+			position: relative;
+			display: flex;
+			flex-direction: column;
+			justify-content: center;
+		}
+
+		#checkbox-selected {
+			align-self: center;
+			width: 24px;
+			height: 24px;
+		}
+
+		#button-swap {
+			width: 32px;
+			height: 32px;
+			padding: 0px;
+			position: absolute;
+			bottom: 0px;
+		}
+	`;
+
+	// @ts-ignore
+	render() {
+		let embeddedElement;
+		switch (this.queueEntry.type) {
+			case "Page":
+				embeddedElement = html`<document-queue-entry-page .document=${this.queueEntry} .api=${this.api}></document-queue-entry-page>`; break;
+			case "Separator":
+				embeddedElement = html`<document-queue-entry-separator .document=${this.queueEntry} .api=${this.api}></document-queue-entry-separator>`; break;
+			default:
+				embeddedElement = html`<span>Unsupported entry type!</span>`
+		}
+
+		return html`
+			<div id="left-bar">
+				<input id="checkbox-selected" type="checkbox" .checked=${this.selected} @change=${this.onCheckboxChange}></input>
+				<button id="button-swap" @click=${e => this.api.queueShift(1, this.queueEntry.id)}>⇵</button>
+			</div>
+
+			${embeddedElement}
+		`;
+	}
+
+	/** @param {Event} event */
+	onCheckboxChange(event) {
+		// @ts-ignore
+		this.selected = event.target.checked;
+
+		/** @type {CustomEventInit<DocumentQueueEntryEventChangeSelectionDetails>} */
+		const eventData = { detail: { selected: this.selected } };
+		this.dispatchEvent(new CustomEvent("changeselection", eventData));
+	}
+
+	/**
+	 * Used for FLIP animations.
+	 * @type {DOMRect}
+	 */
+	#oldBoundingClientRect;
+
+	prepareFLIP() {
+		this.#oldBoundingClientRect = this.getBoundingClientRect();
+	}
+
+	doFLIP() {
+		const oldRect = this.#oldBoundingClientRect;
+		if (oldRect == undefined) {
+			return;
+		}
+
+		const newRect = this.getBoundingClientRect();
+
+		const deltaX = oldRect.left - newRect.left;
+		const deltaY = oldRect.top - newRect.top;
+
+		if (Math.abs(deltaX) >= 1 || Math.abs(deltaY) >= 1) {
+			this.animate([{
+				transform: `translate(${deltaX}px, ${deltaY}px)`
+			}, {
+				transform: 'none'
+			}], {
+				duration: 150,
+				easing: 'ease-out',
+				fill: 'both',
+			});
+		}
+	}
+}
+
+customElements.define("document-queue-entry", DocumentQueueEntry);
--- a/static/js/components/document-queue.js
+++ b/static/js/components/document-queue.js
@ -0,0 +1,169 @@
+import { API } from '../api.js';
+import { DocumentQueueEntry } from './document-queue-entry.js'
+
+/** @typedef {{selectedIDs: number[], allIDs: number[]}} DocumentQueueEventChangeSelectionDetails */
+/** @typedef {CustomEvent<DocumentQueueEventChangeSelectionDetails>} DocumentQueueEventChangeSelection */
+
+// TODO: Use LitElement, and use repeat directive, which also keeps the DOM state when shuffling elements around
+export class DocumentQueue extends HTMLElement {
+	/** @type {API|undefined} */
+	#api;
+
+	/** @param {API} api */
+	set api(api) {
+		this.#api = api;
+
+		this.#api.addEventListener("queuedeleteat", /** @param {import("model").APIEvents["queuedeleteat"]} event */(event) => {
+			this.queueDeleteAt(event.detail.indexA, event.detail.indexB);
+		});
+		this.#api.addEventListener("queueinsertat", /** @param {import("model").APIEvents["queueinsertat"]} event */(event) => {
+			this.queueInsertAt(event.detail.index, event.detail.documents);
+		});
+		this.#api.addEventListener("queueshiftat", /** @param {import("model").APIEvents["queueshiftat"]} event */(event) => {
+			this.queueShiftAt(event.detail.index, event.detail.offset);
+		});
+		this.#api.addEventListener("queuereplace", /** @param {import("model").APIEvents["queuereplace"]} event */(event) => {
+			this.queueReplace(event.detail.documents);
+		});
+	}
+
+	connectedCallback() {
+		this.style.display = "flex";
+		this.style.gap = "8px";
+		this.style.flexDirection = "column";
+		this.style.padding = "8px";
+	}
+
+	selectionInfo() {
+		const children = Array.from(this.children);
+
+		const result = {};
+		result.selectedIDs = children.filter(/** @param {DocumentQueueEntry} value */ value => { return value.selected; }).map(/** @param {DocumentQueueEntry} value */(value) => { return value.queueEntry.id; });
+		result.allIDs = children.map(/** @param {DocumentQueueEntry} value */ value => { return value.queueEntry.id; });
+
+		return result;
+	}
+
+	updateSelection() {
+		/** @type {CustomEventInit<DocumentQueueEventChangeSelectionDetails>} */
+		const eventData = { detail: this.selectionInfo() };
+		this.dispatchEvent(new CustomEvent("changeselection", eventData));
+	}
+
+	/**
+	 * 
+	 * @param {boolean} state 
+	 */
+	selectAll(state) {
+		const children = Array.from(this.children);
+
+		children.forEach(/** @param {DocumentQueueEntry} child */ child => {
+			child.selected = state;
+		});
+	}
+
+	/**
+	 * Deletes a range of documents.
+	 * @param {number} indexA // Start index.
+	 * @param {number} indexB // End index. (Not included in the range).
+	 */
+	queueDeleteAt(indexA, indexB) {
+		// Store positions.
+		Array.from(this.children).forEach(/** @param {DocumentQueueEntry} child */ child => {
+			child.prepareFLIP();
+		});
+
+		if (this.hasChildNodes()) {
+			const children = this.children;
+			for (let i = indexA; i < indexB; i++) {
+				this.removeChild(children[i]);
+			}
+		}
+
+		// Start FLIP animation.
+		Array.from(this.children).forEach(/** @param {DocumentQueueEntry} child */ child => {
+			child.doFLIP();
+		});
+
+		this.updateSelection();
+	}
+
+	/**
+	 * Inserts a range of documents at the given index.
+	 * @param {number} index
+	 * @param {import('model').APIQueueEntry[]} documents
+	 */
+	queueInsertAt(index, documents) {
+		// Store positions.
+		Array.from(this.children).forEach(/** @param {DocumentQueueEntry} child */ child => {
+			child.prepareFLIP();
+		});
+
+		documents.forEach(document => {
+			if (this.hasChildNodes() || this.children.length === index) {
+				const newChild = this.appendChild(new DocumentQueueEntry());
+				newChild.api = this.#api;
+				newChild.queueEntry = document;
+				newChild.addEventListener("changeselection", e => this.updateSelection());
+			} else {
+				const newChild = this.insertBefore(new DocumentQueueEntry(), this.childNodes[index]);
+				newChild.api = this.#api;
+				newChild.queueEntry = document;
+				newChild.addEventListener("changeselection", e => this.updateSelection());
+			}
+			index++;
+		});
+
+		// Start FLIP animation.
+		Array.from(this.children).forEach(/** @param {DocumentQueueEntry} child */ child => {
+			child.doFLIP();
+		});
+
+		this.updateSelection();
+	}
+
+	/**
+	 * Replaces all documents currently in the list/queue.
+	 * @param {import('model').APIQueueEntry[]} documents
+	 */
+	queueReplace(documents) {
+		this.innerHTML = "";
+
+		documents.forEach(document => {
+			const newChild = this.appendChild(new DocumentQueueEntry());
+			newChild.api = this.#api;
+			newChild.queueEntry = document;
+			newChild.addEventListener("changeselection", e => this.updateSelection());
+		});
+
+		this.updateSelection();
+	}
+
+	/**
+	 * Shifts a single document entry by the given offset.
+	 * @param {number} index
+	 * @param {number} offset
+	 */
+	queueShiftAt(index, offset) {
+		// Store positions.
+		Array.from(this.children).forEach(/** @param {DocumentQueueEntry} child */ child => {
+			child.prepareFLIP();
+		});
+
+		const child = this.children[index];
+		child.remove();
+		const newIndex = index + offset;
+		if (!this.hasChildNodes() || this.children.length === newIndex) {
+			this.appendChild(child);
+		} else {
+			this.insertBefore(child, this.children[newIndex]);
+		}
+
+		// Start FLIP animation.
+		Array.from(this.children).forEach(/** @param {DocumentQueueEntry} child */ child => {
+			child.doFLIP();
+		});
+	}
+}
+
+customElements.define("document-queue", DocumentQueue);
--- a/static/js/model.d.ts
+++ b/static/js/model.d.ts
@ -0,0 +1,41 @@
+export interface APIQueueEntry {
+	id: number;
+	name: string;
+	type: string;
+	page: string | undefined;
+}
+
+export type APIPacketQueueDelete = {
+	ids: number[];
+}
+
+export type APIPacketQueueDeleteAt = {
+	indexA: number;
+	indexB: number;
+}
+
+export type APIPacketQueueInsertAt = {
+	index: number;
+	documents: APIQueueEntry[];
+}
+
+export type APIPacketQueueReplace = {
+	documents: APIQueueEntry[];
+}
+
+export type APIPacketQueueShiftAt = {
+	index: number;
+	offset: number;
+}
+
+export type APIPacketQueueShift = {
+	ids: number[];
+	offset: number;
+}
+
+export type APIEvents = {
+	queuedeleteat: CustomEvent<APIPacketQueueDeleteAt>;
+	queueinsertat: CustomEvent<APIPacketQueueInsertAt>;
+	queuereplace: CustomEvent<APIPacketQueueReplace>;
+	queueshiftat: CustomEvent<APIPacketQueueShiftAt>;
+}
--- a/static/js/vendor/lit-html/lit-all.min.js
+++ b/static/js/vendor/lit-html/lit-all.min.js
--- a/static/js/vendor/lit-html/lit-all.min.js.map
+++ b/static/js/vendor/lit-html/lit-all.min.js.map
--- a/static/styles.css
+++ b/static/styles.css
@ -0,0 +1,16 @@
+body {
+	font-family: sans-serif;
+	margin: 0;
+}
+
+#main-container {
+	height: 100vh;
+	width: 100vw;
+	display: flex;
+	flex-direction: column;
+}
+
+#main-container > document-queue {
+	overflow-y: auto;
+	flex-grow: 1;
+}
--- a/test-documents/.gitignore
+++ b/test-documents/.gitignore
@ -0,0 +1,3 @@
+*
+
+!.gitignore
--- a/unit/consts.go
+++ b/unit/consts.go
@ -0,0 +1,3 @@
+package unit
+
+const MillimetersPerInch = 25.4
--- a/unit/density.go
+++ b/unit/density.go
@ -0,0 +1,6 @@
+package unit
+
+// Density is representing something unitless per length unit.
+type Density interface {
+	PerMillimeter() PerMillimeter
+}
--- a/unit/inch.go
+++ b/unit/inch.go
@ -0,0 +1,21 @@
+package unit
+
+import "strconv"
+
+// Inch denotes a distance, position or offset in inches.
+type Inch float64
+
+var _ Unit = Inch(0)
+var _ Length = Inch(0)
+
+func (v Inch) String() string {
+	return strconv.FormatFloat(float64(v), 'f', -1, 64) + "\u00A0inch"
+}
+
+func (Inch) UnitSymbol() string {
+	return "inch"
+}
+
+func (v Inch) Millimeters() Millimeter {
+	return Millimeter(v * MillimetersPerInch)
+}
--- a/unit/length.go
+++ b/unit/length.go
@ -0,0 +1,6 @@
+package unit
+
+// Length is something that can represent a distance, offset or position.
+type Length interface {
+	Millimeters() Millimeter
+}
--- a/unit/millimeter.go
+++ b/unit/millimeter.go
@ -0,0 +1,25 @@
+package unit
+
+import "strconv"
+
+// Millimeter denotes a distance, position or offset in millimeters.
+type Millimeter float64
+
+var _ Unit = Millimeter(0)
+var _ Length = Millimeter(0)
+
+func (v Millimeter) String() string {
+	return strconv.FormatFloat(float64(v), 'f', -1, 64) + "\u00A0mm"
+}
+
+func (Millimeter) UnitSymbol() string {
+	return "mm"
+}
+
+func (v Millimeter) Inches() Inch {
+	return Inch(v / MillimetersPerInch)
+}
+
+func (v Millimeter) Millimeters() Millimeter {
+	return v
+}
--- a/unit/page-dimensions.go
+++ b/unit/page-dimensions.go
@ -0,0 +1,52 @@
+package unit
+
+// PageDimensions contains the page size and margins of a scanned document page.
+type PageDimensions[T UnitConstraint] struct {
+	MediumSize Vec2[T]      `json:"mediumSize"` // The size of the page or medium.
+	ScanSize   Rectangle[T] `json:"scanSize"`   // The size of the scanned area or image.
+}
+
+// NewPageDimensionsFromDensity returns page dimensions for the given resolution resX and resY, and the respective densities.
+//
+// The resulting PageDimensions will have equal MediumSize and ScanSize (No margin).
+// The correct margin or MediumSize can be added later on.
+//
+// In case any density is nil, this will return zero value PageDimensions.
+func NewPageDimensionsFromDensity(resX, resY int, densityX, densityY Density) PageDimensions[Millimeter] {
+	if densityX == nil || densityY == nil {
+		return PageDimensions[Millimeter]{}
+	}
+
+	size := Vec2[Millimeter]{
+		X: Millimeter(resX) / Millimeter(densityX.PerMillimeter()),
+		Y: Millimeter(resY) / Millimeter(densityY.PerMillimeter()),
+	}
+
+	return PageDimensions[Millimeter]{
+		MediumSize: size,
+		ScanSize: Rectangle[Millimeter]{
+			Size: size,
+		},
+	}
+}
+
+// NewPageDimensionsFromLengths returns page dimensions for the given lengths.
+//
+// The resulting PageDimensions will have equal MediumSize and ScanSize (No margin).
+// The correct margin or MediumSize can be added later on.
+//
+// In case any length is nil, this will return zero value PageDimensions.
+func NewPageDimensionsFromLengths(x, y Length) PageDimensions[Millimeter] {
+	if x == nil || y == nil {
+		return PageDimensions[Millimeter]{}
+	}
+
+	size := Vec2[Millimeter]{X: x.Millimeters(), Y: y.Millimeters()}
+
+	return PageDimensions[Millimeter]{
+		MediumSize: size,
+		ScanSize: Rectangle[Millimeter]{
+			Size: size,
+		},
+	}
+}
--- a/unit/per-inch.go
+++ b/unit/per-inch.go
@ -0,0 +1,21 @@
+package unit
+
+import "strconv"
+
+// PerInch denotes a density of something unitless per inch.
+type PerInch float64
+
+var _ Unit = PerInch(0)
+var _ Density = PerInch(0)
+
+func (v PerInch) String() string {
+	return strconv.FormatFloat(float64(v), 'f', -1, 64) + "/inch"
+}
+
+func (PerInch) UnitSymbol() string {
+	return "/inch"
+}
+
+func (v PerInch) PerMillimeter() PerMillimeter {
+	return PerMillimeter(v / MillimetersPerInch)
+}
--- a/unit/per-millimeter.go
+++ b/unit/per-millimeter.go
@ -0,0 +1,25 @@
+package unit
+
+import "strconv"
+
+// PerMillimeter denotes a density of something unitless per millimeter.
+type PerMillimeter float64
+
+var _ Unit = PerMillimeter(0)
+var _ Density = PerMillimeter(0)
+
+func (v PerMillimeter) String() string {
+	return strconv.FormatFloat(float64(v), 'f', -1, 64) + "/mm"
+}
+
+func (PerMillimeter) UnitSymbol() string {
+	return "/mm"
+}
+
+func (v PerMillimeter) PerInch() PerInch {
+	return PerInch(v * MillimetersPerInch)
+}
+
+func (v PerMillimeter) PerMillimeter() PerMillimeter {
+	return v
+}
--- a/unit/rectangle.go
+++ b/unit/rectangle.go
@ -0,0 +1,6 @@
+package unit
+
+type Rectangle[T UnitConstraint] struct {
+	Origin Vec2[T] // The offset of the rectangle.
+	Size   Vec2[T] // The dimensions of the rectangle.
+}
--- a/unit/unit.go
+++ b/unit/unit.go
@ -0,0 +1,12 @@
+package unit
+
+type Unit interface {
+	UnitSymbol() string
+}
+
+// UnitConstraint can be used as generic type constraints for Unit.
+type UnitConstraint interface {
+	Unit
+
+	~float64
+}
--- a/unit/unitless.go
+++ b/unit/unitless.go
@ -0,0 +1,10 @@
+package unit
+
+// Unitless is a "Unit" for something without dimension.
+type Unitless float64
+
+var _ Unit = Unitless(0)
+
+func (Unitless) UnitSymbol() string {
+	return ""
+}
--- a/unit/vec-2.go
+++ b/unit/vec-2.go
@ -0,0 +1,62 @@
+package unit
+
+import (
+	"math"
+	"strconv"
+)
+
+// Vec2 is a 2D vector of values with the unit of T.
+type Vec2[T UnitConstraint] struct {
+	X T `json:"x"`
+	Y T `json:"y"`
+}
+
+// NewVec2FromVec2 takes an arbitrary Vec2 and returns it as a new vector with the type T.
+func NewVec2FromVec2[I, T UnitConstraint](a Vec2[I]) Vec2[T] {
+	return Vec2[T]{T(a.X), T(a.Y)}
+}
+
+func (a Vec2[T]) String() string {
+	return "(" +
+		strconv.FormatFloat(float64(a.X), 'f', -1, 64) + ", " +
+		strconv.FormatFloat(float64(a.Y), 'f', -1, 64) +
+		")\u00A0" + T.UnitSymbol(0)
+}
+
+func (a Vec2[T]) EqualWithPrecision(b Vec2[T], precision T) bool {
+	if math.Abs(float64(a.X-b.X)) > float64(precision) {
+		return false
+	}
+	if math.Abs(float64(a.Y-b.Y)) > float64(precision) {
+		return false
+	}
+	return true
+}
+
+func (a Vec2[T]) Unitless() Vec2[Unitless] {
+	return Vec2[Unitless]{Unitless(a.X), Unitless(a.Y)}
+}
+
+func (a Vec2[T]) Added(b Vec2[T]) Vec2[T] {
+	return Vec2[T]{a.X + b.X, a.Y + b.Y}
+}
+
+func (a Vec2[T]) Subed(b Vec2[T]) Vec2[T] {
+	return Vec2[T]{a.X - b.X, a.Y - b.Y}
+}
+
+func (a Vec2[T]) Scaled(s float64) Vec2[T] {
+	return Vec2[T]{a.X * T(s), a.Y * T(s)}
+}
+
+func (a Vec2[T]) Normalized() Vec2[Unitless] {
+	return a.Scaled(1 / float64(a.Length())).Unitless()
+}
+
+func (a Vec2[T]) LengthSqr() T {
+	return a.X*a.X + a.Y*a.Y
+}
+
+func (a Vec2[T]) Length() T {
+	return T(math.Abs(float64(a.LengthSqr())))
+}
--- a/util.go
+++ b/util.go
@ -0,0 +1,26 @@
+package main
+
+import (
+	"Scanyonero/document"
+	"log"
+	"path/filepath"
+)
+
+func LoadExampleQueueEntries() []QueueEntry {
+	ingestor := document.Ingestor{DefaultDPI: 600}
+
+	pages, err := ingestor.Ingest(document.MustLoadFile(filepath.Join("test-documents", "300 DPI Feeder.jpg")))
+	if err != nil {
+		log.Panicf("Failed to ingest document: %v", err)
+	}
+
+	var entries []QueueEntry
+	for _, page := range pages {
+		entries = append(entries, QueueEntry{
+			ID:             NewQueueEntryID(),
+			QueueEntryData: QueueEntryDataPage{Page: &page},
+		})
+	}
+
+	return entries
+}