package x

import "image"

import "github.com/jezek/xgbutil"
// 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 {
		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:
			<- 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) 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
}


// 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

	// 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
	windowWidth, windowHeight := backend.calculateWindowSize()
	backend.window.Create (
		backend.connection.RootWin(),
		0, 0, windowWidth, windowHeight,
		0)
	backend.window.Map()

	// 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)
}