//go:build wasm

package glfw

import (
	"errors"
	"fmt"
	"io"
	"log"
	"net/http"
	"runtime"
	"syscall/js"
)

const (
	True     int = 1
	False    int = 0
	DontCare int = -1
)

var document = js.Global().Get("document")

var contextWatcher ContextWatcher

func Init(cw ContextWatcher) error {
	contextWatcher = cw
	return nil
}

func Terminate() error {
	return nil
}

//gocyclo:ignore
func CreateWindow(_, _ int, title string, monitor *Monitor, share *Window) (*Window, error) {
	// THINK: Consider https://developer.mozilla.org/en-US/docs/Web/API/Window.open?
	body := document.Get("body")
	if body.Equal(js.Null()) {
		body = document.Call("createElement", "body")
		document.Set("body", body)
	}

	body.Get("style").Call("setProperty", "margin", "0")

	canvas := document.Call("createElement", "canvas")

	body.Call("appendChild", canvas)

	// HACK: Go fullscreen /* canvas being sized asynchronously, we are using body the window inner Width/Height */?
	width := js.Global().Get("innerWidth").Int()
	height := js.Global().Get("innerHeight").Int()

	devicePixelRatio := js.Global().Get("devicePixelRatio").Float()
	canvas.Set("width", int(float64(width)*devicePixelRatio+0.5))   // Nearest non-negative int.
	canvas.Set("height", int(float64(height)*devicePixelRatio+0.5)) // Nearest non-negative int.

	// Use dvw and dvh if supported; otherwise, fall back to vw and vh.
	style := canvas.Get("style")
	setProperty := style.Get("setProperty").Call("bind", style)
	setProperty.Invoke("width", "100vw")
	setProperty.Invoke("width", "100dvw")
	setProperty.Invoke("height", "100vh")
	setProperty.Invoke("height", "100dvh")

	document.Set("title", title)

	// Use glfw hints.
	attrs := defaultAttributes()
	attrs.Alpha = (hints[AlphaBits] > 0)
	if _, ok := hints[DepthBits]; ok {
		attrs.Depth = (hints[DepthBits] > 0)
	}
	attrs.Stencil = (hints[StencilBits] > 0)
	attrs.Antialias = (hints[Samples] > 0)
	attrs.PremultipliedAlpha = (hints[PremultipliedAlpha] > 0)
	attrs.PreserveDrawingBuffer = (hints[PreserveDrawingBuffer] > 0)
	attrs.PreferLowPowerToHighPerformance = (hints[PreferLowPowerToHighPerformance] > 0)
	attrs.FailIfMajorPerformanceCaveat = (hints[FailIfMajorPerformanceCaveat] > 0)

	// Create GL context.
	context, err := newContext(canvas, attrs)
	if context.Equal(js.Value{}) {
		return nil, err
	}

	w := &Window{
		canvas:           canvas,
		context:          context,
		devicePixelRatio: devicePixelRatio,
	}

	if w.canvas.Get("requestPointerLock").Equal(js.Undefined()) ||
		document.Get("exitPointerLock").Equal(js.Undefined()) {

		w.missing.pointerLock = true
	}
	if w.canvas.Get("webkitRequestFullscreen").Equal(js.Undefined()) ||
		document.Get("webkitExitFullscreen").Equal(js.Undefined()) {

		w.missing.fullscreen = true
	}

	if monitor != nil {
		if w.missing.fullscreen {
			log.Println("warning: Fullscreen API unsupported")
		} else {
			w.requestFullscreen = true
		}
	}

	w.eventHandlerCleanups = make([]func(), 0, 11)
	newJsFuncFrom := func(handler func(this js.Value, args []js.Value) any) js.Func {
		function := js.FuncOf(handler)
		w.eventHandlerCleanups = append(w.eventHandlerCleanups, function.Release)
		return function
	}

	addGlobalEventListener := js.Global().Get("addEventListener").Call("bind", js.Global())

	addGlobalEventListener.Invoke("focus", newJsFuncFrom(func(this js.Value, args []js.Value) any {
		if w.focusCallback != nil {
			w.focusCallback(w, true)
		}
		return nil
	}))

	addGlobalEventListener.Invoke("blur", newJsFuncFrom(func(this js.Value, args []js.Value) any {
		if w.focusCallback != nil {
			w.focusCallback(w, false)
		}
		return nil
	}))

	addGlobalEventListener.Invoke("resize", newJsFuncFrom(func(this js.Value, args []js.Value) any {
		// HACK: Go fullscreen?
		w.devicePixelRatio = js.Global().Get("devicePixelRatio").Float()
		widthScaled, heightScaled := w.GetSize()
		canvas.Set("width", widthScaled)
		canvas.Set("height", heightScaled)

		if w.framebufferSizeCallback != nil {
			// TODO: Callbacks may be blocking so they need to happen asyncronously. However,
			//       GLFW API promises the callbacks will occur from one thread (i.e., sequentially), so may want to do that.
			widthFramebuffer, heightFramebuffer := w.GetFramebufferSize()
			go w.framebufferSizeCallback(w, widthFramebuffer, heightFramebuffer)
		}
		if w.sizeCallback != nil {
			go w.sizeCallback(w, widthScaled, heightScaled)
		}
		return nil
	}))

	addDocumentEventListener := document.Get("addEventListener").Call("bind", document)

	addDocumentEventListener.Invoke("keydown", newJsFuncFrom(func(this js.Value, args []js.Value) any {
		ke := args[0]
		w.goFullscreenIfRequested()

		action := Press
		if ke.Get("repeat").Bool() {
			action = Repeat
		}

		key := toKey(ke)

		// Extend slice if needed.
		neededSize := int(key) + 1
		if neededSize > len(w.keys) {
			w.keys = append(w.keys, make([]Action, neededSize-len(w.keys))...)
		}
		w.keys[key] = action
		mods := toModifierKey(ke)
		if w.keyCallback != nil {
			go w.keyCallback(w, key, -1, action, mods)
		}

		if w.charCallback != nil && mods < 2 {
			keyStr := ke.Get("key").String()
			if len(keyStr) == 1 {
				keyRune := []rune(keyStr)
				go w.charCallback(w, keyRune[0])
			}
		}

		ke.Call("preventDefault")
		return nil
	}))
	addDocumentEventListener.Invoke("keyup", newJsFuncFrom(func(this js.Value, args []js.Value) any {
		ke := args[0]
		w.goFullscreenIfRequested()

		key := toKey(ke)

		// Extend slice if needed.
		neededSize := int(key) + 1
		if neededSize > len(w.keys) {
			w.keys = append(w.keys, make([]Action, neededSize-len(w.keys))...)
		}
		w.keys[key] = Release

		if w.keyCallback != nil {
			mods := toModifierKey(ke)

			go w.keyCallback(w, key, -1, Release, mods)
		}

		ke.Call("preventDefault")
		return nil
	}))
	addDocumentEventListener.Invoke("mousedown", newJsFuncFrom(func(this js.Value, args []js.Value) any {
		me := args[0]
		w.goFullscreenIfRequested()

		button := me.Get("button").Int()
		if !(button >= 0 && button <= 2) {
			return nil
		}

		w.mouseButton[button] = Press
		if w.mouseButtonCallback != nil {
			go w.mouseButtonCallback(w, MouseButton(button), Press, 0)
		}

		me.Call("preventDefault")
		return nil
	}))
	addDocumentEventListener.Invoke("mouseup", newJsFuncFrom(func(this js.Value, args []js.Value) any {
		me := args[0]
		w.goFullscreenIfRequested()

		button := me.Get("button").Int()
		if !(button >= 0 && button <= 2) {
			return nil
		}

		w.mouseButton[button] = Release
		if w.mouseButtonCallback != nil {
			go w.mouseButtonCallback(w, MouseButton(button), Release, 0)
		}

		me.Call("preventDefault")
		return nil
	}))
	addDocumentEventListener.Invoke("contextmenu", newJsFuncFrom(func(this js.Value, args []js.Value) any {
		me := args[0]
		me.Call("preventDefault")
		return nil
	}))

	addDocumentEventListener.Invoke("mousemove", newJsFuncFrom(func(this js.Value, args []js.Value) any {
		me := args[0]
		var movementX, movementY float64
		if !w.missing.pointerLock {
			movementX = me.Get("movementX").Float()
			movementY = me.Get("movementY").Float()
		} else {
			movementX = me.Get("clientX").Float() - w.cursorPos[0]
			movementY = me.Get("clientY").Float() - w.cursorPos[1]
		}
		movementX *= w.devicePixelRatio
		movementY *= w.devicePixelRatio

		w.cursorPos[0], w.cursorPos[1] = me.Get("clientX").Float()*w.devicePixelRatio, me.Get("clientY").Float()*w.devicePixelRatio
		if w.cursorPosCallback != nil {
			go w.cursorPosCallback(w, w.cursorPos[0], w.cursorPos[1])
		}
		if w.mouseMovementCallback != nil {
			go w.mouseMovementCallback(w, w.cursorPos[0], w.cursorPos[1], movementX, movementY)
		}
		me.Call("preventDefault")
		return nil
	}))
	addDocumentEventListener.Invoke("wheel", newJsFuncFrom(func(this js.Value, args []js.Value) any {
		we := args[0]

		deltaX := we.Get("deltaX").Float()
		deltaY := we.Get("deltaY").Float()

		var multiplier float64
		/*
			switch we.DeltaMode {
			case dom.DeltaPixel:
				multiplier = 0.1
			case dom.DeltaLine:
				multiplier = 1
			default:
				log.Println("unsupported WheelEvent.DeltaMode:", we.DeltaMode)
				multiplier = 1
			}*/
		multiplier = 1

		if w.scrollCallback != nil {
			go w.scrollCallback(w, -deltaX*multiplier, -deltaY*multiplier)
		}

		we.Call("preventDefault")
		return nil
	}))

	/*
		// Hacky mouse-emulation-via-touch.
		touchHandler := func(event dom.Event) {
			w.goFullscreenIfRequested()

			te := event.(*dom.TouchEvent)

			touches := te.Get("touches")
			if touches.Length() > 0 {
				t := touches.Index(0)

				if w.touches != nil && w.touches.Length() > 0 { // This event is a movement only if we previously had > 0 touch points.
					if w.mouseMovementCallback != nil {
						go w.mouseMovementCallback(w, t.Get("clientX").Float(), t.Get("clientY").Float(), t.Get("clientX").Float()-w.cursorPos[0], t.Get("clientY").Float()-w.cursorPos[1])
					}
				}

				w.cursorPos[0], w.cursorPos[1] = t.Get("clientX").Float(), t.Get("clientY").Float()
				if w.cursorPosCallback != nil {
					go w.cursorPosCallback(w, w.cursorPos[0], w.cursorPos[1])
				}
			}
			w.touches = touches

			te.PreventDefault()
		}
		document.AddEventListener("touchstart", false, touchHandler)
		document.AddEventListener("touchmove", false, touchHandler)
		document.AddEventListener("touchend", false, touchHandler)*/

	addDocumentEventListener.Invoke("beforeUnload", newJsFuncFrom(func(this js.Value, args []js.Value) any {
		if w.closeCallback != nil {
			w.closeCallback(w)
		}
		return nil
	}))

	// Request first animation frame.
	w.requestAnimationFrame = js.Global().Get("requestAnimationFrame").Call("bind", js.Global())
	w.requestAnimationFrame.Invoke(animationFrameCallback)

	return w, nil
}

func (w *Window) SetAttrib(attrib Hint, value int) {
	// TODO: Implement.
}

func SwapInterval(interval int) error {
	// TODO: Implement.
	return nil
}

type Window struct {
	canvas            js.Value
	context           js.Value
	requestFullscreen bool // requestFullscreen is set to true when fullscreen should be entered as soon as possible (in a user input handler).
	fullscreen        bool // fullscreen is true if we're currently in fullscreen mode.

	// Unavailable browser APIs.
	missing struct {
		pointerLock bool // Pointer Lock API.
		fullscreen  bool // Fullscreen API.
	}

	devicePixelRatio float64

	cursorMode  int
	cursorPos   [2]float64
	mouseButton [3]Action

	keys []Action

	cursorPosCallback       CursorPosCallback
	mouseMovementCallback   MouseMovementCallback
	mouseButtonCallback     MouseButtonCallback
	keyCallback             KeyCallback
	scrollCallback          ScrollCallback
	charCallback            CharCallback
	framebufferSizeCallback FramebufferSizeCallback
	sizeCallback            SizeCallback
	focusCallback           FocusCallback
	closeCallback           CloseCallback

	touches js.Value // Hacky mouse-emulation-via-touch.

	eventHandlerCleanups  []func()
	requestAnimationFrame js.Value
}

func (w *Window) SetPos(xpos, ypos int) {
	fmt.Println("not implemented: SetPos:", xpos, ypos)
}

func (w *Window) SetSize(width, height int) {
	fmt.Println("not implemented: SetSize:", width, height)
}

func (w *Window) SetIcon(images any) {
	// images is actually of type []image.Image, but no need to import image until we actually do something with it
	fmt.Println("not implemented: SetIcon")
}

// goFullscreenIfRequested performs webkitRequestFullscreen if it was scheduled. It is called only from
// user events, because that API will fail if called at any other time.
func (w *Window) goFullscreenIfRequested() {
	if !w.requestFullscreen {
		return
	}
	w.requestFullscreen = false
	w.canvas.Call("webkitRequestFullscreen")
	w.fullscreen = true
}

type Monitor struct{}

func (m *Monitor) GetVideoMode() *VidMode {
	return &VidMode{
		// HACK: Hardcoded sample values.
		// TODO: Try to get real values from browser via some API, if possible.
		Width:       1680,
		Height:      1050,
		RedBits:     8,
		GreenBits:   8,
		BlueBits:    8,
		RefreshRate: 60,
	}
}

func GetPrimaryMonitor() *Monitor {
	// TODO: Implement real functionality.
	return &Monitor{}
}

func (w *Window) SetMonitor(monitor *Monitor, xpos, ypos, width, height, refreshRate int) {
	// TODO: Implement real functionality.
}

func PollEvents() error {
	return nil
}

func (w *Window) MakeContextCurrent() {
	contextWatcher.OnMakeCurrent(w.context)
}

func DetachCurrentContext() {
	contextWatcher.OnDetach()
}

func GetCurrentContext() *Window {
	panic("not implemented")
}

type CursorPosCallback func(w *Window, xpos float64, ypos float64)

func (w *Window) SetCursorPosCallback(cbfun CursorPosCallback) (previous CursorPosCallback) {
	w.cursorPosCallback = cbfun

	// TODO: Handle previous.
	return nil
}

type MouseMovementCallback func(w *Window, xpos float64, ypos float64, xdelta float64, ydelta float64)

func (w *Window) SetMouseMovementCallback(cbfun MouseMovementCallback) (previous MouseMovementCallback) {
	w.mouseMovementCallback = cbfun

	// TODO: Handle previous.
	return nil
}

type KeyCallback func(w *Window, key Key, scancode int, action Action, mods ModifierKey)

func (w *Window) SetKeyCallback(cbfun KeyCallback) (previous KeyCallback) {
	w.keyCallback = cbfun

	// TODO: Handle previous.
	return nil
}

type CharCallback func(w *Window, char rune)

func (w *Window) SetCharCallback(cbfun CharCallback) (previous CharCallback) {
	w.charCallback = cbfun

	// TODO: Handle previous.
	return nil
}

type ScrollCallback func(w *Window, xoff float64, yoff float64)

func (w *Window) SetScrollCallback(cbfun ScrollCallback) (previous ScrollCallback) {
	w.scrollCallback = cbfun

	// TODO: Handle previous.
	return nil
}

type MouseButtonCallback func(w *Window, button MouseButton, action Action, mods ModifierKey)

func (w *Window) SetMouseButtonCallback(cbfun MouseButtonCallback) (previous MouseButtonCallback) {
	w.mouseButtonCallback = cbfun

	// TODO: Handle previous.
	return nil
}

type FramebufferSizeCallback func(w *Window, width int, height int)

func (w *Window) SetFramebufferSizeCallback(cbfun FramebufferSizeCallback) (previous FramebufferSizeCallback) {
	w.framebufferSizeCallback = cbfun

	// TODO: Handle previous.
	return nil
}

// Nearest non-negative int.
func (w *Window) scaleRound(f float64) int {
	return int(f*w.devicePixelRatio + 0.5)
}

func (w *Window) GetSize() (width, height int) {
	return w.scaleRound(w.canvas.Get("clientWidth").Float()), w.scaleRound(w.canvas.Get("clientHeight").Float())
}

func (w *Window) GetFramebufferSize() (width, height int) {
	return w.canvas.Get("width").Int(), w.canvas.Get("height").Int()
}

func (w *Window) GetPos() (x, y int) {
	// Not implemented.
	return
}

func (w *Window) ShouldClose() bool {
	return false
}

func (w *Window) SetShouldClose(value bool) {
	// TODO: Implement.
	// THINK: What should happen in the browser if we're told to "close" the window. Do we destroy/remove the canvas? Or nothing?
	//        Perhaps https://developer.mozilla.org/en-US/docs/Web/API/Window.close is relevant.
}

func (w *Window) SwapBuffers() error {
	<-animationFrameChan
	w.requestAnimationFrame.Invoke(animationFrameCallback)

	return nil
}

var animationFrameChan = make(chan struct{}, 1)

var animationFrameCallback = js.FuncOf(func(this js.Value, args []js.Value) any {
	animationFrameChan <- struct{}{}

	return nil
})

func (w *Window) GetCursorPos() (x, y float64) {
	return w.cursorPos[0], w.cursorPos[1]
}

var keyWarnings = 10

func (w *Window) GetKey(key Key) Action {
	if key == -1 && keyWarnings > 0 {
		// TODO: Implement all keys, get rid of this.
		keyWarnings--
		log.Println("GetKey: key not implemented.")
		return Release
	}
	if int(key) >= len(w.keys) {
		return Release
	}
	return w.keys[key]
}

func (w *Window) GetMouseButton(button MouseButton) Action {
	if !(button >= 0 && button <= 2) {
		panic(fmt.Errorf("button is out of range: %v", button))
	}

	// Hacky mouse-emulation-via-touch.
	if !w.touches.Equal(js.Value{}) {
		switch button {
		case MouseButton1:
			if w.touches.Length() == 1 || w.touches.Length() == 3 {
				return Press
			}
		case MouseButton2:
			if w.touches.Length() == 2 || w.touches.Length() == 3 {
				return Press
			}
		}

		return Release
	}

	return w.mouseButton[button]
}

func (w *Window) GetInputMode(mode InputMode) int {
	switch mode {
	case CursorMode:
		return w.cursorMode
	default:
		panic(errors.New("not implemented"))
	}
}

var (
	ErrInvalidParameter = errors.New("invalid parameter")
	ErrInvalidValue     = errors.New("invalid value")
)

func (w *Window) SetInputMode(mode InputMode, value int) {
	switch mode {
	case CursorMode:
		// TODO; Make cursor API compatible with GLFW and Fyne use/expectation.
		/*
			// Temporarily disable cursor change
			if w.missing.pointerLock {
				log.Println("warning: Pointer Lock API unsupported")
				return
			}
			switch value {
			case CursorNormal:
				w.cursorMode = value
				document.Call("exitPointerLock")
				w.canvas.Get("style").Call("setProperty", "cursor", "initial")
				return
			case CursorHidden:
				w.cursorMode = value
				document.Call("exitPointerLock")
				w.canvas.Get("style").Call("setProperty", "cursor", "none")
				return
			case CursorDisabled:
				w.cursorMode = value
				w.canvas.Call("requestPointerLock")
				return
			default:
				panic(ErrInvalidValue)
			}
		*/
		return
	case StickyKeysMode:
		panic(errors.New("not implemented"))
	case StickyMouseButtonsMode:
		panic(errors.New("not implemented"))
	default:
		panic(ErrInvalidParameter)
	}
}

type Key int

// TODO: Keys defined as -iota-2 need to be set to a valid positive value that matches the keyCode
//
//	generated by browsers. -iota-2 is used as a temporary solution to have unique but invalid values.
//	See https://developer.mozilla.org/en-US/docs/Web/API/KeyboardEvent/keyCode.
const (
	KeyUnknown      Key = -1
	KeySpace        Key = 32
	KeyApostrophe   Key = 222
	KeyComma        Key = 188
	KeyMinus        Key = 189
	KeyPeriod       Key = 190
	KeySlash        Key = 191
	Key0            Key = 48
	Key1            Key = 49
	Key2            Key = 50
	Key3            Key = 51
	Key4            Key = 52
	Key5            Key = 53
	Key6            Key = 54
	Key7            Key = 55
	Key8            Key = 56
	Key9            Key = 57
	KeySemicolon    Key = 186
	KeyEqual        Key = 187
	KeyA            Key = 65
	KeyB            Key = 66
	KeyC            Key = 67
	KeyD            Key = 68
	KeyE            Key = 69
	KeyF            Key = 70
	KeyG            Key = 71
	KeyH            Key = 72
	KeyI            Key = 73
	KeyJ            Key = 74
	KeyK            Key = 75
	KeyL            Key = 76
	KeyM            Key = 77
	KeyN            Key = 78
	KeyO            Key = 79
	KeyP            Key = 80
	KeyQ            Key = 81
	KeyR            Key = 82
	KeyS            Key = 83
	KeyT            Key = 84
	KeyU            Key = 85
	KeyV            Key = 86
	KeyW            Key = 87
	KeyX            Key = 88
	KeyY            Key = 89
	KeyZ            Key = 90
	KeyLeftBracket  Key = 219
	KeyBackslash    Key = 220
	KeyRightBracket Key = 221
	KeyGraveAccent  Key = 192
	KeyWorld1       Key = -iota - 2
	KeyWorld2       Key = -iota - 2
	KeyEscape       Key = 27
	KeyEnter        Key = 13
	KeyTab          Key = 9
	KeyBackspace    Key = 8
	KeyInsert       Key = -iota - 2
	KeyDelete       Key = 46
	KeyRight        Key = 39
	KeyLeft         Key = 37
	KeyDown         Key = 40
	KeyUp           Key = 38
	KeyPageUp       Key = -iota - 2
	KeyPageDown     Key = -iota - 2
	KeyHome         Key = -iota - 2
	KeyEnd          Key = -iota - 2
	KeyCapsLock     Key = 20
	KeyScrollLock   Key = -iota - 2
	KeyNumLock      Key = -iota - 2
	KeyPrintScreen  Key = -iota - 2
	KeyPause        Key = -iota - 2
	KeyF1           Key = 112
	KeyF2           Key = 113
	KeyF3           Key = 114
	KeyF4           Key = 115
	KeyF5           Key = 116
	KeyF6           Key = 117
	KeyF7           Key = 118
	KeyF8           Key = 119
	KeyF9           Key = 120
	KeyF10          Key = 121
	KeyF11          Key = 122
	KeyF12          Key = 123
	KeyF13          Key = -iota - 2
	KeyF14          Key = -iota - 2
	KeyF15          Key = -iota - 2
	KeyF16          Key = -iota - 2
	KeyF17          Key = -iota - 2
	KeyF18          Key = -iota - 2
	KeyF19          Key = -iota - 2
	KeyF20          Key = -iota - 2
	KeyF21          Key = -iota - 2
	KeyF22          Key = -iota - 2
	KeyF23          Key = -iota - 2
	KeyF24          Key = -iota - 2
	KeyF25          Key = -iota - 2
	KeyKP0          Key = -iota - 2
	KeyKP1          Key = -iota - 2
	KeyKP2          Key = -iota - 2
	KeyKP3          Key = -iota - 2
	KeyKP4          Key = -iota - 2
	KeyKP5          Key = -iota - 2
	KeyKP6          Key = -iota - 2
	KeyKP7          Key = -iota - 2
	KeyKP8          Key = -iota - 2
	KeyKP9          Key = -iota - 2
	KeyKPDecimal    Key = -iota - 2
	KeyKPDivide     Key = -iota - 2
	KeyKPMultiply   Key = -iota - 2
	KeyKPSubtract   Key = -iota - 2
	KeyKPAdd        Key = -iota - 2
	KeyKPEnter      Key = -iota - 2
	KeyKPEqual      Key = -iota - 2
	KeyLeftShift    Key = 340
	KeyLeftControl  Key = 341
	KeyLeftAlt      Key = 342
	KeyLeftSuper    Key = 91
	KeyRightShift   Key = 344
	KeyRightControl Key = 345
	KeyRightAlt     Key = 346
	KeyRightSuper   Key = 93
	KeyMenu         Key = -iota - 2
)

// toKey extracts Key from given KeyboardEvent.
func toKey(ke js.Value) Key {
	// TODO: Factor out into DOM package.
	const (
		KeyLocationLeft  = 1
		KeyLocationRight = 2
	)

	key := Key(ke.Get("keyCode").Int())
	switch {
	case key == 16 && ke.Get("location").Int() == KeyLocationLeft:
		key = KeyLeftShift
	case key == 16 && ke.Get("location").Int() == KeyLocationRight:
		key = KeyRightShift
	case key == 17 && ke.Get("location").Int() == KeyLocationLeft:
		key = KeyLeftControl
	case key == 17 && ke.Get("location").Int() == KeyLocationRight:
		key = KeyRightControl
	case key == 18 && ke.Get("location").Int() == KeyLocationLeft:
		key = KeyLeftAlt
	case key == 18 && ke.Get("location").Int() == KeyLocationRight:
		key = KeyRightAlt
	}
	return key
}

// toModifierKey extracts ModifierKey from given KeyboardEvent.
func toModifierKey(ke js.Value) ModifierKey {
	mods := ModifierKey(0)
	if ke.Get("shiftKey").Bool() {
		mods += ModShift
	}
	if ke.Get("ctrlKey").Bool() {
		mods += ModControl
	}
	if ke.Get("altKey").Bool() {
		mods += ModAlt
	}
	if ke.Get("metaKey").Bool() {
		mods += ModSuper
	}
	return mods
}

type MouseButton int

const (
	MouseButton1 MouseButton = 0
	MouseButton2 MouseButton = 2 // Web MouseEvent has middle and right mouse buttons in reverse order.
	MouseButton3 MouseButton = 1 // Web MouseEvent has middle and right mouse buttons in reverse order.

	MouseButtonLeft   = MouseButton1
	MouseButtonRight  = MouseButton2
	MouseButtonMiddle = MouseButton3
)

type Joystick int

const (
	Joystick1 Joystick = iota
	Joystick2
	Joystick3
	Joystick4
	Joystick5
	Joystick6
	Joystick7
	Joystick8
	Joystick9
	Joystick10
	Joystick11
	Joystick12
	Joystick13
	Joystick14
	Joystick15
	Joystick16

	JoystickLast = Joystick16
)

type GamepadAxis int

const (
	AxisLeftX GamepadAxis = iota
	AxisLeftY
	AxisRightX
	AxisRightY
	AxisLeftTrigger
	AxisRightTrigger

	AxisLast = AxisRightTrigger
)

type GamepadButton int

const (
	ButtonA GamepadButton = iota
	ButtonB
	ButtonX
	ButtonY
	ButtonLeftBumper
	ButtonRightBumper
	ButtonBack
	ButtonStart
	ButtonGuide
	ButtonLeftThumb
	ButtonRightThumb
	ButtonDpadUp
	ButtonDpadRight
	ButtonDpadDown
	ButtonDpadLeft

	ButtonLast     = ButtonDpadLeft
	ButtonCross    = ButtonA
	ButtonCircle   = ButtonB
	ButtonSquare   = ButtonX
	ButtonTriangle = ButtonY
)

type Action int

const (
	Release Action = 0
	Press   Action = 1
	Repeat  Action = 2
)

type InputMode int

const (
	CursorMode InputMode = iota
	StickyKeysMode
	StickyMouseButtonsMode
	LockKeyMods
	RawMouseMotion
)

const (
	CursorNormal = iota
	CursorHidden
	CursorDisabled
)

type ModifierKey int

const (
	ModShift ModifierKey = (1 << iota)
	ModControl
	ModAlt
	ModSuper
)

func (joy Joystick) IsPresent() bool {
	// TODO: Implement.
	return false
}

func (joy Joystick) GetGamepadName() string {
	// TODO: Implement.
	return "Gamepad"
}

func (joy Joystick) GetButtons() []Action {
	// TODO: Implement.
	return make([]Action, 0)
}

func (joy Joystick) GetAxes() []float32 {
	// TODO: Implement.
	return make([]float32, 0)
}

// Open opens a named asset. It's the caller's responsibility to close it when done.
func Open(name string) (io.ReadCloser, error) {
	resp, err := http.Get(name)
	if err != nil {
		return nil, err
	}
	if resp.StatusCode != 200 {
		return nil, fmt.Errorf("non-200 status: %s", resp.Status)
	}
	return resp.Body, nil
}

// ---

func WaitEvents() {
	// TODO.

	runtime.Gosched()
}

func PostEmptyEvent() {
	// TODO: Implement.
}

func DefaultWindowHints() {
	// TODO: Implement.
}

func (w *Window) SetClipboardString(str string) {
	SetClipboardString(str)
}

func (w *Window) GetClipboardString() string {
	return GetClipboardString()
}

func (w *Window) SetTitle(title string) {
	document.Set("title", title)
}

func (w *Window) Show() {
	// TODO: Implement.
}

func (w *Window) Hide() {
	// TODO: Implement.
}

func (w *Window) Destroy() {
	document.Get("body").Call("removeChild", w.canvas)
	if w.fullscreen {
		if w.missing.fullscreen {
			log.Println("warning: Fullscreen API unsupported")
		} else {
			document.Call("webkitExitFullscreen")
			w.fullscreen = false
		}
	}

	for _, free := range w.eventHandlerCleanups {
		free()
	}
}

type CloseCallback func(w *Window)

func (w *Window) SetCloseCallback(cbfun CloseCallback) (previous CloseCallback) {
	previous = w.closeCallback
	w.closeCallback = cbfun
	return previous
}

type RefreshCallback func(w *Window)

func (w *Window) SetRefreshCallback(cbfun RefreshCallback) (previous RefreshCallback) {
	// TODO: Implement.

	// TODO: Handle previous.
	return nil
}

type SizeCallback func(w *Window, width int, height int)

func (w *Window) SetSizeCallback(cbfun SizeCallback) (previous SizeCallback) {
	w.sizeCallback = cbfun

	// TODO: Handle previous.
	return nil
}

type CursorEnterCallback func(w *Window, entered bool)

func (w *Window) SetCursorEnterCallback(cbfun CursorEnterCallback) (previous CursorEnterCallback) {
	// TODO: Implement.

	// TODO: Handle previous.
	return nil
}

type CharModsCallback func(w *Window, char rune, mods ModifierKey)

func (w *Window) SetCharModsCallback(cbfun CharModsCallback) (previous CharModsCallback) {
	// TODO: Implement.

	// TODO: Handle previous.
	return nil
}

type PosCallback func(w *Window, xpos int, ypos int)

func (w *Window) SetPosCallback(cbfun PosCallback) (previous PosCallback) {
	// TODO: Implement.

	// TODO: Handle previous.
	return nil
}

type FocusCallback func(w *Window, focused bool)

func (w *Window) SetFocusCallback(cbfun FocusCallback) (previous FocusCallback) {
	previous = w.focusCallback
	w.focusCallback = cbfun
	return previous
}

type IconifyCallback func(w *Window, iconified bool)

func (w *Window) SetIconifyCallback(cbfun IconifyCallback) (previous IconifyCallback) {
	// TODO: Implement.

	// TODO: Handle previous.
	return nil
}

type DropCallback func(w *Window, names []string)

func (w *Window) SetDropCallback(cbfun DropCallback) (previous DropCallback) {
	// TODO: Implement. Can use HTML5 file drag and drop API?

	// TODO: Handle previous.
	return nil
}