package x

import "image"
import "image/color"
// 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 { })
	}
	
	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) {
	
}

func (backend *Backend) SetIcon (icons []image.Image) {
	
}

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 {
			// TODO: resize and rebind canvas
		}
	}
}

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)
}

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

	// calculate metrics
	// TODO: base these off of font metrics
	backend.metrics.cellWidth  = 8
	backend.metrics.cellHeight = 16
	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)

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

	for i := 8; i < 64; i ++ {
		backend.canvas.Set(8, i, color.RGBA { R: 0xFF, A: 0xFF })
	}
	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)
}