package pixel

import "time"
import "golang.org/x/image/font"
import "github.com/faiface/pixel"
import "github.com/faiface/pixel/pixelgl"
import "golang.org/x/image/font/basicfont"
import "git.tebibyte.media/sashakoshka/stone"

type Backend struct {
	window         *pixelgl.Window
	boundsDirty    bool
	previousBounds pixel.Vec
	fontFace       font.Face
	application    *stone.Application
	config         *stone.Config

	metrics struct {
		cellWidth  int
		cellHeight int
	}
}

func (backend *Backend) Run (callback func (application *stone.Application)) {
	if backend.fontFace == nil {
		backend.fontFace = basicfont.Face7x13
	}

	faceMetrics := backend.fontFace.Metrics()
	backend.metrics.cellHeight = faceMetrics.Height.Round()
	// FIXME?: this might not be the best way to get the cell width
	faceAdvance, ok := backend.fontFace.GlyphAdvance('M')
	if ok {
		backend.metrics.cellWidth = faceAdvance.Round()
	} else {
		backend.metrics.cellWidth = backend.metrics.cellHeight / 2
	}
	
	pixelgl.Run (func () {
		var err error
		backend.window, err = pixelgl.NewWindow (pixelgl.WindowConfig {
			Resizable:   true,
			Undecorated: true,
			VSync:       true,
			NoIconify:   true,
			Title:       backend.application.Title(),
			Bounds:      backend.calculateWindowSize(),
		})
		backend.Poll()
		
		if err != nil { panic(err.Error()) }
		callback(backend.application)
	})
}

func (backend *Backend) Await (timeout time.Duration) (keepRunning bool) {
	if backend.window == nil {
		panic("call to Backend.Await before window exists")
	}

	backend.draw()
	backend.window.UpdateInputWait(timeout)
	backend.processEvents()
	keepRunning = !backend.window.Closed()
	return
}

func (backend *Backend) Poll () (keepRunning bool) {
	if backend.window == nil {
		panic("call to Backend.Poll before window exists")
	}

	backend.draw()
	backend.window.UpdateInput()
	backend.processEvents()
	keepRunning = !backend.window.Closed()
	return
}

func (backend *Backend) SetTitle (title string) {
	if backend.window != nil {
		backend.window.SetTitle(title)
	}
}

func (backend *Backend) draw () {
	didDrawing := false

	if backend.boundsDirty {
		backend.window.Clear (
			backend.config.Color(stone.ColorApplication))
		backend.boundsDirty = false
		didDrawing = true
	} else {
		// TODO: clear out dirty cells before drawing them (we don't
		// want to clear them out if we have already just cleared
		// everything out)

		
	}

	// TODO: draw dirty cells.
	width, height := backend.application.Size()
	for x := 0; x < width; x ++ {
		for y := 0; y < height; y ++ {
			clean := backend.application.Clean(x, y)
			// cell  := application.content[index]
			if clean { continue }

			// draw cell
			
			didDrawing = true // TODO: set didDrawing up there ^
			backend.application.MarkClean(x, y)
		}
	}

	if didDrawing {
		backend.window.SwapBuffers()
	}
}

func (backend *Backend) processEvents () {
	
}

func (backend *Backend) calculateWindowSize () (bounds pixel.Rect) {
	width, height := backend.application.Size()
	bounds = pixel.R (
		0, 0,
		float64(width  * backend.metrics.cellWidth),
		float64(height * backend.metrics.cellHeight))
	return
}

func factory (application *stone.Application) (output stone.Backend, err error) {
	backend := &Backend {
		application: application,
		config:      application.Config(),
	}
	output = backend
	return
}

func init () {
	stone.RegisterBackend(factory)
}