package x

import "image"
import "golang.org/x/image/font"
import "golang.org/x/image/font/basicfont"

import "github.com/jezek/xgb"
import "github.com/jezek/xgbutil"
import "github.com/jezek/xgb/xproto"
import "github.com/jezek/xgbutil/ewmh"
import "github.com/jezek/xgbutil/xevent"
import "github.com/jezek/xgbutil/xwindow"
import "github.com/jezek/xgbutil/xgraphics"


import "git.tebibyte.media/sashakoshka/stone"

type Backend struct {
	application *stone.Application
	config      *stone.Config
	connection  *xgbutil.XUtil
	window      *xwindow.Window
	canvas      *xgraphics.Image
	channel     chan(stone.Event)

	ping struct {
		before chan(struct { })
		after  chan(struct { })
		quit   chan(struct { })
	}

	font struct {
		face font.Face
	}
	
	metrics struct {
		windowWidth  int
		windowHeight int
		cellWidth    int
		cellHeight   int
		padding      int
		paddingX     int
		paddingY     int
		descent      int
	}
}

func (backend *Backend) Run (channel chan(stone.Event)) {
	backend.channel = channel
	
	for {
		select {
		case <- backend.ping.before:
			// if the queue is empty, don't dequeue anything because
			// it would cause a fucking segfault lmao (???)
			if !xevent.Empty(backend.connection) {
				event, err := xevent.Dequeue(backend.connection)
				if err != nil {
					// TODO: do something with err
				}

				if event != nil {
					backend.handleXEvent(event)
				}
			}
			
			<- backend.ping.after

		case <- backend.ping.quit:
			backend.shutDown()
			return
		}
	}
}

func (backend *Backend) SetTitle (title string) (err error) {
	err = ewmh.WmNameSet(backend.connection, backend.window.Id, title)
	return
}

func (backend *Backend) SetIcon (icons []image.Image) (err error) {
	wmIcons := []ewmh.WmIcon { }
	
	for _, icon := range icons {
		width  := icon.Bounds().Max.X
		height := icon.Bounds().Max.Y
		wmIcon := ewmh.WmIcon {
			Width:  uint(width),
			Height: uint(height),
			Data:   make ([]uint, width * height),
		}

		// manually convert image data beacuse of course we have to do
		// this
		index := 0
		for y := 0; y < height; y ++ {
		for x := 0; x < width;  x ++ {
			r, g, b, a := icon.At(x, y).RGBA()
			r >>= 8
			g >>= 8
			b >>= 8
			a >>= 8
			wmIcon.Data[index] =
				(uint(a) << 24) |
				(uint(r) << 16) |
				(uint(g) << 8)  |
				(uint(b) << 0)
			index ++
		}}
		
		wmIcons = append(wmIcons, wmIcon)
	}

	err = ewmh.WmIconSet(backend.connection, backend.window.Id, wmIcons)
	return
}

func (backend *Backend) handleXEvent (event xgb.Event) {
	switch event.(type) {
	case xproto.ConfigureNotifyEvent:
		configureEvent := event.(xproto.ConfigureNotifyEvent)
		
		newWidth  := int(configureEvent.Width)
		newHeight := int(configureEvent.Height)
		sizeChanged :=
			backend.metrics.windowWidth  != newWidth ||
			backend.metrics.windowHeight != newHeight
		backend.metrics.windowWidth  = newWidth
		backend.metrics.windowHeight = newHeight

		if sizeChanged {
			// compress events
			configureEvent =
				backend.compressConfigureNotify(configureEvent)
		
			// resize and rebind canvas
			backend.canvas.Destroy()
			backend.canvas = xgraphics.New (
				backend.connection,
				image.Rect (
					0, 0,
					backend.metrics.windowWidth,
					backend.metrics.windowHeight))
			// FIXME (?): this doesn't work. if it were to work, it
			// would possibly be a cleaner way to resize the canvas.
			// backend.canvas.Scale (
				// backend.metrics.windowWidth,
				// backend.metrics.windowHeight)
			backend.drawRune(8, 16, 'X')
			backend.bindCanvas()
		}
	}
}

func (backend *Backend) compressConfigureNotify (
	firstEvent xproto.ConfigureNotifyEvent,
) (
	lastEvent xproto.ConfigureNotifyEvent,
) {
	backend.connection.Sync()
	xevent.Read(backend.connection, false)
	lastEvent = firstEvent
	
	for index, untypedEvent := range xevent.Peek(backend.connection) {
		if untypedEvent.Err != nil { continue }
		
		typedEvent, ok := untypedEvent.Event.(xproto.ConfigureNotifyEvent)
		if !ok { continue }

		lastEvent = typedEvent
		defer func (index int) {
			xevent.DequeueAt(backend.connection, index)
		} (index)
	}

	return
}

func (backend *Backend) shutDown () {
	backend.channel <- stone.EventQuit { }
}

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

func (backend *Backend) bindCanvas () {
	backend.canvas.XSurfaceSet(backend.window.Id)
	backend.canvas.XDraw()
	backend.canvas.XPaint(backend.window.Id)
}

func (backend *Backend) drawRune (x, y int, character rune) {
	
}

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

	// load font
	// TODO: load this from a file
	backend.font.face = basicfont.Face7x13

	// calculate metrics
	metrics := backend.font.face.Metrics()
	glyphAdvance, _ := backend.font.face.GlyphAdvance('M')
	backend.metrics.cellWidth  = glyphAdvance.Round()
	backend.metrics.cellHeight = metrics.Height.Round()
	backend.metrics.descent    = metrics.Descent.Round()
	backend.metrics.padding =
		backend.config.Padding() *
		backend.metrics.cellHeight
	backend.metrics.paddingX = backend.metrics.padding
	backend.metrics.paddingY = backend.metrics.padding
	backend.metrics.windowWidth,
	backend.metrics.windowHeight = backend.calculateWindowSize()

	// connect to X
	backend.connection, err = xgbutil.NewConn()
	if err != nil { return }
	backend.window, err = xwindow.Generate(backend.connection)
	if err != nil { return }

	// create the window
	backend.window.Create (
		backend.connection.RootWin(),
		0, 0,
		backend.metrics.windowWidth, backend.metrics.windowHeight,
		0)
	backend.window.Map()
	backend.window.Listen(xproto.EventMaskStructureNotify)
	backend.SetTitle(application.Title())
	backend.SetIcon(application.Icon())

	// create a canvas
	backend.canvas = xgraphics.New (
		backend.connection,
		image.Rect (
			0, 0,
			backend.metrics.windowWidth,
			backend.metrics.windowHeight))
	backend.bindCanvas()

	// attatch graceful close handler
	backend.window.WMGracefulClose (func (window *xwindow.Window) {
		backend.window.Destroy()
		backend.shutDown()
	})

	// start event loop
	backend.ping.before,
	backend.ping.after,
	backend.ping.quit = xevent.MainPing(backend.connection)
	
	output = backend
	return
}

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