package pixel

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

// Backend represents an instance of the pixel backend
type Backend struct {
	window            *pixelgl.Window
	boundsDirty       bool
	windowBounds      pixel.Vec
	fontFace          font.Face
	application       *stone.Application
	config            *stone.Config
	backgroundStamper *imdraw.IMDraw
	fontAtlas         *text.Atlas
	textDrawer        *text.Text
	showBounds        bool
	showCellBounds    bool

	metrics struct {
		cellWidth  int
		cellHeight int
		padding    int
		paddingX   int
		paddingY   int
		descent    int
	}
}

// Run satisfies the Run method of the Backend interface. Due to the nature of
// pixel, this will forcibly bind to the main thread.
func (backend *Backend) Run (callback func (application *stone.Application)) {
	// backend.showBounds     = true
	// backend.showCellBounds = true
	
	if backend.fontFace == nil {
		backend.fontFace = basicfont.Face7x13
	}

	backend.backgroundStamper = imdraw.New(nil)
	backend.fontAtlas = text.NewAtlas(backend.fontFace, text.ASCII)
	backend.textDrawer = text.New(pixel.V(0, 0), backend.fontAtlas)

	backend.metrics.descent    = int(backend.fontAtlas.Descent())
	backend.metrics.cellHeight = int(backend.fontAtlas.LineHeight())
	// 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 () {
		// construct the window, and all that
		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()

		// TODO: this should return the error and not panic
		if err != nil { panic(err.Error()) }
		callback(backend.application)
	})
}

// Await fulfills the Await method of the Backend interface.
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
}

// Poll fulfills the Poll method of the Backend interface.
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
}

// SetTitle fulfills the SetTitle method of the Backend interface.
func (backend *Backend) SetTitle (title string) {
	if backend.window != nil {
		backend.window.SetTitle(title)
	}
}

// JustPressed fulfills the JustPressed method of the Backend interface.
func (backend *Backend) JustPressed (button stone.Button) (pressed bool) {
	pressed = backend.window.JustPressed(pixelgl.Button(button))
	return
}

// JustReleased fulfills the JustReleased method of the Backend interface.
func (backend *Backend) JustReleased (button stone.Button) (released bool) {
	released = backend.window.JustReleased(pixelgl.Button(button))
	return
}

// Pressed fulfills the Pressed method of the Backend interface.
func (backend *Backend) Pressed (button stone.Button) (pressed bool) {
	pressed = backend.window.Pressed(pixelgl.Button(button))
	return
}

// Repeated fulfills the Repeated method of the Backend interface.
func (backend *Backend) Repeated (button stone.Button) (repeated bool) {
	repeated = backend.window.Repeated(pixelgl.Button(button))
	return
}

// Typed fulfills the Typed method of the Backend interface.
func (backend *Backend) Typed () (text string) {
	text = backend.window.Typed()
	return
}

// Resized fulfills the Resized method of the Backend interface.
func (backend *Backend) Resized () (resized bool) {
	resized = backend.boundsDirty
	return
}

// MousePosition fulfills the MousePosition method of the Backend interface.
func (backend *Backend) MousePosition () (x, y int) {
	vector := backend.window.MousePosition()
	x = int (
		(vector.X - float64(backend.metrics.paddingX)) /
		float64(backend.metrics.cellWidth))
	y = int (
		(backend.windowBounds.Y -
			vector.Y -
			float64(backend.metrics.paddingY)) /
		float64(backend.metrics.cellHeight))
	return
}

// draw renders updates to the screen.
func (backend *Backend) draw () {
	// didDrawing := false
	width, height := backend.application.Size()
	
	if backend.boundsDirty {
		backend.window.Clear (
			backend.config.Color(stone.ColorApplication))
		backend.boundsDirty = false
		// didDrawing = true
	} else {
		// clear out dirty cells before drawing them. this is in an else
		// block because if the bounds were dirty, we have already
		// cleared the entire screen.

		backend.backgroundStamper.Clear()
		backend.backgroundStamper.Color =
			backend.config.Color(stone.ColorApplication)
		for x := 0; x < width; x ++ {
			for y := 0; y < height; y ++ {
				clean := backend.application.Clean(x, y)
				if clean { continue }

				backend.backgroundStamper.Push (
					backend.vectorAtPosition(x, y),
					backend.vectorAtPosition(x + 1, y + 1))
				backend.backgroundStamper.Rectangle(0)
				// didDrawing = true

				if backend.showCellBounds {
					backend.backgroundStamper.Color =
					backend.config.Color(stone.ColorForeground)
					backend.backgroundStamper.Push (
						backend.vectorAtPosition(x, y),
						backend.vectorAtPosition(x + 1, y + 1))
					backend.backgroundStamper.Rectangle(1)
					backend.backgroundStamper.Color =
						backend.config.Color(stone.ColorApplication)
				}
			}
		}
		backend.backgroundStamper.Draw(backend.window)
	}

	backend.textDrawer.Clear()
	backend.textDrawer.Color = 
		backend.config.Color(stone.ColorForeground)
	for x := 0; x < width; x ++ {
		for y := 0; y < height; y ++ {
			clean := backend.application.Clean(x, y)
			if clean { continue }
			backend.application.MarkClean(x, y)

			cell := backend.application.Cell(x, y)
			content := cell.Rune()
			if content < 32 { continue }
			
			// draw cell
			backend.textDrawer.Dot = pixel.V (
				float64 (
					x * backend.metrics.cellWidth +
					backend.metrics.paddingX),
				backend.windowBounds.Y - float64 (
					(y + 1) * backend.metrics.cellHeight +
					backend.metrics.paddingY -
					backend.metrics.descent))
			
			backend.textDrawer.WriteRune(content)
			backend.textDrawer.Draw(backend.window, pixel.IM)
		}
	}

	// draw a rectangle around the buffer if we are showing bounds
	if backend.showBounds {
		backend.backgroundStamper.Clear()
		backend.backgroundStamper.Color =
			backend.config.Color(stone.ColorBackground)
		backend.backgroundStamper.Push (
			backend.vectorAtPosition(0, 0),
			backend.vectorAtPosition(width, height))
		backend.backgroundStamper.Rectangle(1)
		backend.backgroundStamper.Draw(backend.window)
	}

	backend.window.SwapBuffers()
}

// processEvents reacts to events recieved from pixel, resizing and
// recalculating things as need be.
func (backend *Backend) processEvents () {
	newBounds := backend.window.Bounds().Max
	backend.boundsDirty = backend.windowBounds != newBounds
	backend.windowBounds = newBounds
	
	if backend.boundsDirty {
		// calculate padding
		backend.metrics.padding =
			backend.config.Padding() *
			backend.metrics.cellWidth
		deadArea := float64(backend.metrics.padding * 2)

		// calculate new width and height for buffer
		width := int (
			(backend.windowBounds.X - deadArea) /
			float64(backend.metrics.cellWidth))
		height := int (
			(backend.windowBounds.Y - deadArea) /
			float64(backend.metrics.cellHeight))
		backend.application.SetSize(width, height)

		// position buffer in center of screen
		frameWidth  := width * backend.metrics.cellWidth
		frameHeight := height * backend.metrics.cellHeight
		backend.metrics.paddingX = (int(backend.windowBounds.X) - frameWidth)  / 2
		backend.metrics.paddingY = (int(backend.windowBounds.Y) - frameHeight) / 2
	}
}

// vectorAtPosition generates a pixel vector at the top left of the specified
// cell.
func (backend *Backend) vectorAtPosition (x, y int) (vector pixel.Vec) {
	vector = pixel.V (
		float64 (
			x * backend.metrics.cellWidth +
			backend.metrics.paddingX),
		backend.windowBounds.Y - float64 (
			y * backend.metrics.cellHeight +
			backend.metrics.paddingY))
	return
}

// calculateWindowSize calculates window bounds based on the internal buffer
// size.
func (backend *Backend) calculateWindowSize () (bounds pixel.Rect) {
	width, height := backend.application.Size()
	bounds = pixel.R (
		0, 0,
		float64 (
			width  * backend.metrics.cellWidth +
			backend.metrics.padding * 2),
		float64 (
			height * backend.metrics.cellHeight +
			backend.metrics.padding * 2))
	return
}

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

// init registers this backend when the program starts.
func init () {
	stone.RegisterBackend(factory)
}