package navigation

import (
	"git.d3nexus.de/Dadido3/D3vugu-components/components/input"
	"github.com/vugu/vugu"
)

type Pagination struct {
	AttrMap vugu.AttrMap

	buttons []paginationButtonInfo

	Bind PaginationBinder

	Paginate PaginateHandler // External handler that is called upon an event.
}

type paginationButtonInfo struct {
	Page  int
	Class string
}

// Page returns the currently selected page as a 1-based index.
// A result of 0 means there is no selected page.
func (c *Pagination) Page() int {
	if c.Bind == nil {
		return 0
	}

	return c.Bind.PaginationPage()
}

// Pages returns the total page number that this pagination component shows.
func (c *Pagination) Pages() int {
	if c.Bind == nil {
		return 0
	}

	return c.Bind.PaginationPages()
}

func (c *Pagination) handleClickPrev(event input.ClickEvent) {
	c.handleClickPage(event, c.Page()-1)
}

func (c *Pagination) handleClickNext(event input.ClickEvent) {
	c.handleClickPage(event, c.Page()+1)
}

func (c *Pagination) handleClickPage(event input.ClickEvent, page int) {
	pages := c.Pages()

	if page <= 0 || page > pages {
		return
	}

	if c.Bind != nil {
		c.Bind.SetPaginationPage(page)
	}

	if c.Paginate != nil {
		c.Paginate.PaginateHandle(PaginateEvent{
			DOMEvent: event,
			PaginationInfo: PaginationInfo{
				Page:  page,
				Pages: pages,
			},
		})
	}
}

func (c *Pagination) Compute(ctx vugu.ComputeCtx) {
	page, pages := c.Page(), c.Pages()

	// Number of buttons around the current page.
	// Excluding first and last page.
	const AroundButtons = 2

	// Number of buttons that can change, so excluding first and last page.
	const DynamicButtons = AroundButtons + 1 + AroundButtons

	// Number of buttons with page numbers, so excluding "previous" and "next".
	const TotalButtons = 1 + DynamicButtons + 1

	// Prepare buttons.
	buttons := [TotalButtons]paginationButtonInfo{
		0:                {Page: 1},
		TotalButtons - 1: {Page: pages},
	}

	startPage := 2
	if startPage < page-AroundButtons {
		startPage = page - AroundButtons
	}
	if startPage > pages-DynamicButtons {
		startPage = pages - DynamicButtons
	}

	for i := 0; i < DynamicButtons; i++ {
		buttons[i+1] = paginationButtonInfo{Page: i + startPage}
	}

	// Remove duplicates and set class accordingly.
	// pageCounter is used to check if pages are strictly monotonically increasing.
	buttonsFiltered := make([]paginationButtonInfo, 0, len(buttons))
	pageCounter := 0
	for _, pageInfo := range buttons {
		if pageCounter < pageInfo.Page && pageInfo.Page <= pages {
			pageCounter = pageInfo.Page
			if pageInfo.Page == page {
				pageInfo.Class = "d3c-button-highlight"
			}
			buttonsFiltered = append(buttonsFiltered, pageInfo)
		}
	}

	c.buttons = buttonsFiltered
}