package x

import "os"
// import "fmt"
import "sync"
import "image"
import "image/draw"
import "golang.org/x/image/font"
import "golang.org/x/image/math/fixed"
import "golang.org/x/image/font/opentype"
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"

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

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

	drawLock sync.Mutex

	font struct {
		face font.Face
	}

	colors [4]xgraphics.BGRA
	
	metrics struct {
		windowWidth  int
		windowHeight int
		cellWidth    int
		cellHeight   int
		padding      int
		paddingX     int
		paddingY     int
		descent      int
	}

	memory struct {
		windowWidth  int
		windowHeight int
	}
}

func (backend *Backend) Run (channel chan(stone.Event)) {
	backend.channel = channel
	xevent.Main(backend.connection)
	backend.shutDown()
}

func (backend *Backend) Draw () {
	backend.drawLock.Lock()
	defer backend.drawLock.Unlock()

	boundsChanged :=
		backend.memory.windowWidth  != backend.metrics.windowWidth ||
		backend.memory.windowHeight != backend.metrics.windowHeight
	backend.memory.windowWidth  = backend.metrics.windowWidth
	backend.memory.windowHeight = backend.metrics.windowHeight

	if boundsChanged {
		backend.reallocateCanvas()
		backend.drawCells(true)
		backend.canvas.XDraw()
		backend.canvas.XPaint(backend.window.Id)
	} else {
		backend.updateWindowAreas(backend.drawCells(false)...)
	}
}

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) handleConfigureNotify (
	connection *xgbutil.XUtil,
	event xevent.ConfigureNotifyEvent,
) {
	configureEvent := *event.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 {
		configureEvent =
			backend.compressConfigureNotify(configureEvent)
		backend.application.SetSize(backend.calculateBufferSize())
		backend.channel <- stone.EventResize { }
	}
}

func (backend *Backend) handleButtonPress (
	connection *xgbutil.XUtil,
	event xevent.ButtonPressEvent,
) {
	buttonEvent := *event.ButtonPressEvent
	backend.channel <- stone.EventPress(buttonEvent.Detail)
}

func (backend *Backend) handleButtonRelease (
	connection *xgbutil.XUtil,
	event xevent.ButtonReleaseEvent,
) {
	buttonEvent := *event.ButtonReleaseEvent
	backend.channel <- stone.EventRelease(buttonEvent.Detail)
}

func (backend *Backend) handleMotionNotify (
	connection *xgbutil.XUtil,
	event xevent.MotionNotifyEvent,
) {
	motionEvent := *event.MotionNotifyEvent
	x, y := backend.cellAt (image.Point {
		X: int(motionEvent.EventX),
		Y: int(motionEvent.EventY),
	})
	backend.channel <- stone.EventMouseMove {
		X: x,
		Y: y,
	}
}

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) calculateBufferSize () (width, height int) {
	width =
		(backend.metrics.windowWidth - backend.metrics.padding * 2) /
		backend.metrics.cellWidth
	height =
		(backend.metrics.windowHeight - backend.metrics.padding * 2) /
		backend.metrics.cellHeight
	return
}

func (backend *Backend) reallocateCanvas () {
	if backend.canvas != nil {
		backend.canvas.Destroy()
	}
	backend.canvas = xgraphics.New (
		backend.connection,
		image.Rect (
			0, 0,
			backend.metrics.windowWidth,
			backend.metrics.windowHeight))
	backend.canvas.For (func (x, y int) xgraphics.BGRA {
		return backend.colors[stone.ColorApplication]
	})
	
	backend.canvas.XSurfaceSet(backend.window.Id)
}

func (backend *Backend) drawCells (forceRedraw bool) (areas []image.Rectangle) {
	width, height := backend.application.Size()
	for y := 0; y < height; y ++ {
	for x := 0; x < width;  x ++ {
		if !forceRedraw && backend.application.Clean(x, y) { continue }
		backend.application.MarkClean(x, y)

		cell := backend.application.Cell(x, y)
		content := cell.Rune()

		if forceRedraw && content < 32 { continue }

		areas = append(areas, backend.boundsOfCell(x, y))
		backend.drawRune(x, y, content)
	}}
	return
}

func (backend *Backend) updateWindowAreas (areas ...image.Rectangle) {
	backend.canvas.XPaintRects(backend.window.Id, areas...)
}

func (backend *Backend) drawRune (x, y int, character rune) {
	// TODO: cache these draws as non-transparent buffers with the
	// application background color as the background. that way, we won't
	// need to redraw the characters *or* composite them.
	
	fillRectangle (
		&image.Uniform {
			C: backend.config.Color(stone.ColorApplication),
		},
		backend.canvas,
		backend.boundsOfCell(x, y))

	if character < 32 { return }
	
	origin := backend.originOfCell(x, y + 1)
	destinationRectangle, mask, maskPoint, _, _ := backend.font.face.Glyph (
		fixed.Point26_6 {
			X: fixed.I(origin.X),
			Y: fixed.I(origin.Y - backend.metrics.descent),
		},
		character)
		
	// strokeRectangle (
		// &image.Uniform {
			// C: backend.config.Color(stone.ColorForeground),
		// },
		// backend.canvas,
		// backend.boundsOfCell(x, y))
		
	draw.DrawMask (
		backend.canvas,
		destinationRectangle,
		&image.Uniform {
			C: backend.config.Color(stone.ColorForeground),
		},
		image.Point { },
		mask,
		maskPoint,
		draw.Over)
}

func (backend *Backend) cellAt (onScreen image.Point) (x, y int) {
	x = (onScreen.X - backend.metrics.paddingX) / backend.metrics.cellWidth
	y = (onScreen.Y - backend.metrics.paddingY) / backend.metrics.cellHeight
	return
}

func (backend *Backend) cellSubImage (x, y int) (cell *xgraphics.Image) {
	cell = backend.canvas.SubImage(backend.boundsOfCell(x, y)).(*xgraphics.Image)
	return
}

func (backend *Backend) originOfCell (x, y int) (origin image.Point) {
	origin = image.Point {
		X: x * backend.metrics.cellWidth  + backend.metrics.paddingX,
		Y: y * backend.metrics.cellHeight + backend.metrics.paddingY,
	}
	return
}

func (backend *Backend) boundsOfCell (x, y int) (bounds image.Rectangle) {
	bounds = image.Rectangle {
		Min: backend.originOfCell(x, y),
		Max: backend.originOfCell(x + 1, y + 1),
	}
	return
}

// 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 }

	// 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())

	// 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)
	
	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
}

func fillRectangle (
	source      image.Image,
	destination draw.Image,
	bounds      image.Rectangle,
) {
	for y := bounds.Min.Y; y < bounds.Max.Y; y ++ {
	for x := bounds.Min.X; x < bounds.Max.X; x ++ {
		destination.Set(x, y, source.At(x, y))
	}}
}

func strokeRectangle (
	source      image.Image,
	destination draw.Image,
	bounds      image.Rectangle,
) {
	x := 0
	y := bounds.Min.Y
	for x = bounds.Min.X; x < bounds.Max.X; x ++ {
		destination.Set(x, y, source.At(x, y))
	}

	y = bounds.Max.Y - 1
	for x = bounds.Min.X; x < bounds.Max.X; x ++ {
		destination.Set(x, y, source.At(x, y))
	}

	x = bounds.Min.X
	for y = bounds.Min.Y; y < bounds.Max.Y; y ++ {
		destination.Set(x, y, source.At(x, y))
	}

	x = bounds.Max.X - 1
	for y = bounds.Min.Y; y < bounds.Max.Y; y ++ {
		destination.Set(x, y, source.At(x, y))
	}
}

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