package navigation

import "github.com/vugu/vugu"

type Pagination struct {
	AttrMap vugu.AttrMap

	buttons []paginationButtonInfo

	Page  int `vugu:"data"`
	Pages int `vugu:"data"`

	Pagination PaginationHandler // External handler that is called upon an event.
}

type paginationButtonInfo struct {
	Page  int
	Class string
}

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

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

func (c *Pagination) handleClickPage(event vugu.DOMEvent, page int) {
	if page <= 0 || page > c.Pages {
		return
	}

	if c.Pagination != nil {
		c.Pagination.PaginationHandle(PaginationEvent{
			DOMEvent: event,
			Page:     page,
		})
	}
}

func (c *Pagination) Init(ctx vugu.InitCtx) {
	c.Pages = 10
}

func (c *Pagination) Compute(ctx vugu.ComputeCtx) {
	// 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: c.Pages},
	}

	startPage := 2
	if startPage < c.Page-AroundButtons {
		startPage = c.Page - AroundButtons
	}
	if startPage > c.Pages-DynamicButtons {
		startPage = c.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 _, page := range buttons {
		if pageCounter < page.Page && page.Page <= c.Pages {
			pageCounter = page.Page
			if page.Page == c.Page {
				page.Class = "d3c-color-accent"
			}
			buttonsFiltered = append(buttonsFiltered, page)
		}
	}

	c.buttons = buttonsFiltered
}