package x

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

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

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

import "github.com/flopp/go-findfont"

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

	// load font
	backend.font.face = findAndLoadFont (
		backend.config.FontName(),
		float64(backend.config.FontSize()))
	if backend.font.face == nil {
		backend.font.face = basicfont.Face7x13
	}

	// pre-calculate colors
	for index := 0; index < len(backend.colors); index ++ {
		color := backend.config.Color(stone.Color(index))
		r, g, b, a := color.RGBA()
		r >>= 8
		g >>= 8
		b >>= 8
		a >>= 8
		backend.colors[index] = xgraphics.BGRA {
			R: uint8(r),
			G: uint8(g),
			B: uint8(b),
			A: uint8(a),
		}
	}

	// 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 }
	keybind.Initialize(backend.connection)

	// create the window
	backend.window.Create (
		backend.connection.RootWin(),
		0, 0,
		backend.metrics.windowWidth, backend.metrics.windowHeight,
		0)
	backend.window.Map()
	// TODO: also listen to mouse movement (compressed) and mouse and
	// keyboard buttons (uncompressed)
	err = backend.window.Listen (
		xproto.EventMaskStructureNotify,
		xproto.EventMaskPointerMotion,
		xproto.EventMaskKeyPress,
		xproto.EventMaskKeyRelease,
		xproto.EventMaskButtonPress,
		xproto.EventMaskButtonRelease)
	backend.SetTitle(application.Title())
	backend.SetIcon(application.Icon())
	if err != nil { return }

	// set minimum dimensions
	minWidth := 
		backend.metrics.cellWidth  + backend.metrics.padding * 2
	minHeight := 
		backend.metrics.cellHeight + backend.metrics.padding * 2
	err = icccm.WmNormalHintsSet (
		backend.connection,
		backend.window.Id,
		&icccm.NormalHints {
			Flags:     icccm.SizeHintPMinSize,
			MinWidth:  uint(minWidth),
			MinHeight: uint(minHeight),
		})
	if err != nil { return }

	// create a canvas
	backend.reallocateCanvas()

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

	// attatch event handlers
	xevent.ConfigureNotifyFun(backend.handleConfigureNotify).
		Connect(backend.connection, backend.window.Id)
	xevent.ButtonPressFun(backend.handleButtonPress).
		Connect(backend.connection, backend.window.Id)
	xevent.ButtonReleaseFun(backend.handleButtonRelease).
		Connect(backend.connection, backend.window.Id)
	xevent.MotionNotifyFun(backend.handleMotionNotify).
		Connect(backend.connection, backend.window.Id)
	xevent.KeyPressFun(backend.handleKeyPress).
		Connect(backend.connection, backend.window.Id)
	xevent.KeyReleaseFun(backend.handleKeyRelease).
		Connect(backend.connection, backend.window.Id)
	
	output = backend
	return
}

func findAndLoadFont (name string, size float64) (face font.Face) {
	if name == "" { return }
	fontPath, err := findfont.Find(name)
	if err != nil { return }
	fontFile, err := os.Open(fontPath)
	if err != nil { return }
	fontObject, err := opentype.ParseReaderAt(fontFile)
	if err != nil { return }
	face, err = opentype.NewFace (fontObject, &opentype.FaceOptions {
		Size: size,
		DPI: 96,
		Hinting: font.HintingFull,
	})
	if err != nil { face = nil }
	
	return
}

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