// Copyright 2014 Hajime Hoshi
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// +build js

package opengl

import (
	"errors"
	"fmt"
	"syscall/js"

	"github.com/hajimehoshi/ebiten/internal/driver"
	"github.com/hajimehoshi/ebiten/internal/jsutil"
	"github.com/hajimehoshi/ebiten/internal/web"
)

type (
	textureNative     js.Value
	framebufferNative js.Value
	shader            js.Value
	buffer            js.Value
	uniformLocation   js.Value

	attribLocation int
	programID      int
	program        struct {
		value js.Value
		id    programID
	}
)

func (t textureNative) equal(rhs textureNative) bool {
	return jsutil.Equal(js.Value(t), js.Value(rhs))
}

func (f framebufferNative) equal(rhs framebufferNative) bool {
	return jsutil.Equal(js.Value(f), js.Value(rhs))
}

func (s shader) equal(rhs shader) bool {
	return jsutil.Equal(js.Value(s), js.Value(rhs))
}

func (b buffer) equal(rhs buffer) bool {
	return jsutil.Equal(js.Value(b), js.Value(rhs))
}

func (u uniformLocation) equal(rhs uniformLocation) bool {
	return jsutil.Equal(js.Value(u), js.Value(rhs))
}

func (p program) equal(rhs program) bool {
	return jsutil.Equal(p.value, rhs.value) && p.id == rhs.id
}

var InvalidTexture = textureNative(js.Null())

func getProgramID(p program) programID {
	return p.id
}

var (
	vertexShader       shaderType
	fragmentShader     shaderType
	arrayBuffer        bufferType
	elementArrayBuffer bufferType
	dynamicDraw        bufferUsage
	streamDraw         bufferUsage
	pixelUnpackBuffer  bufferType
	short              dataType
	float              dataType

	zero             operation
	one              operation
	srcAlpha         operation
	dstAlpha         operation
	oneMinusSrcAlpha operation
	oneMinusDstAlpha operation

	blend               js.Value
	clampToEdge         js.Value
	compileStatus       js.Value
	colorAttachment0    js.Value
	framebuffer_        js.Value
	framebufferBinding  js.Value
	framebufferComplete js.Value
	highFloat           js.Value
	linkStatus          js.Value
	maxTextureSize      js.Value
	nearest             js.Value
	noError             js.Value
	rgba                js.Value
	texture2d           js.Value
	textureMagFilter    js.Value
	textureMinFilter    js.Value
	textureWrapS        js.Value
	textureWrapT        js.Value
	triangles           js.Value
	unpackAlignment     js.Value
	unsignedByte        js.Value
	unsignedShort       js.Value

	texture0 int

	isWebGL2Available bool
)

func init() {
	// Accessing the prototype is rquired on Safari.
	var contextPrototype js.Value
	if !jsutil.Equal(js.Global().Get("WebGL2RenderingContext"), js.Undefined()) {
		contextPrototype = js.Global().Get("WebGL2RenderingContext").Get("prototype")
		isWebGL2Available = true
	} else {
		contextPrototype = js.Global().Get("WebGLRenderingContext").Get("prototype")
	}

	vertexShader = shaderType(contextPrototype.Get("VERTEX_SHADER").Int())
	fragmentShader = shaderType(contextPrototype.Get("FRAGMENT_SHADER").Int())
	arrayBuffer = bufferType(contextPrototype.Get("ARRAY_BUFFER").Int())
	elementArrayBuffer = bufferType(contextPrototype.Get("ELEMENT_ARRAY_BUFFER").Int())
	dynamicDraw = bufferUsage(contextPrototype.Get("DYNAMIC_DRAW").Int())
	streamDraw = bufferUsage(contextPrototype.Get("STREAM_DRAW").Int())
	short = dataType(contextPrototype.Get("SHORT").Int())
	float = dataType(contextPrototype.Get("FLOAT").Int())

	zero = operation(contextPrototype.Get("ZERO").Int())
	one = operation(contextPrototype.Get("ONE").Int())
	srcAlpha = operation(contextPrototype.Get("SRC_ALPHA").Int())
	dstAlpha = operation(contextPrototype.Get("DST_ALPHA").Int())
	oneMinusSrcAlpha = operation(contextPrototype.Get("ONE_MINUS_SRC_ALPHA").Int())
	oneMinusDstAlpha = operation(contextPrototype.Get("ONE_MINUS_DST_ALPHA").Int())

	blend = contextPrototype.Get("BLEND")
	clampToEdge = contextPrototype.Get("CLAMP_TO_EDGE")
	compileStatus = contextPrototype.Get("COMPILE_STATUS")
	colorAttachment0 = contextPrototype.Get("COLOR_ATTACHMENT0")
	framebuffer_ = contextPrototype.Get("FRAMEBUFFER")
	framebufferBinding = contextPrototype.Get("FRAMEBUFFER_BINDING")
	framebufferComplete = contextPrototype.Get("FRAMEBUFFER_COMPLETE")
	highFloat = contextPrototype.Get("HIGH_FLOAT")
	linkStatus = contextPrototype.Get("LINK_STATUS")
	maxTextureSize = contextPrototype.Get("MAX_TEXTURE_SIZE")
	nearest = contextPrototype.Get("NEAREST")
	noError = contextPrototype.Get("NO_ERROR")
	rgba = contextPrototype.Get("RGBA")
	texture0 = contextPrototype.Get("TEXTURE0").Int()
	texture2d = contextPrototype.Get("TEXTURE_2D")
	textureMagFilter = contextPrototype.Get("TEXTURE_MAG_FILTER")
	textureMinFilter = contextPrototype.Get("TEXTURE_MIN_FILTER")
	textureWrapS = contextPrototype.Get("TEXTURE_WRAP_S")
	textureWrapT = contextPrototype.Get("TEXTURE_WRAP_T")
	triangles = contextPrototype.Get("TRIANGLES")
	unpackAlignment = contextPrototype.Get("UNPACK_ALIGNMENT")
	unsignedByte = contextPrototype.Get("UNSIGNED_BYTE")
	unsignedShort = contextPrototype.Get("UNSIGNED_SHORT")

	if isWebGL2Available {
		pixelUnpackBuffer = bufferType(contextPrototype.Get("PIXEL_UNPACK_BUFFER").Int())
	}
}

type contextImpl struct {
	gl            js.Value
	lastProgramID programID
}

func (c *context) ensureGL() {
	if !jsutil.Equal(c.gl, js.Value{}) {
		return
	}

	// TODO: Define id?
	canvas := js.Global().Get("document").Call("querySelector", "canvas")
	attr := js.Global().Get("Object").New()
	attr.Set("alpha", true)
	attr.Set("premultipliedAlpha", true)

	var gl js.Value
	if isWebGL2Available {
		gl = canvas.Call("getContext", "webgl2", attr)
	} else {
		gl = canvas.Call("getContext", "webgl", attr)
		if jsutil.Equal(gl, js.Null()) {
			gl = canvas.Call("getContext", "experimental-webgl", attr)
			if jsutil.Equal(gl, js.Null()) {
				panic("opengl: getContext failed")
			}
		}
	}

	c.gl = gl
}

func (c *context) reset() error {
	c.locationCache = newLocationCache()
	c.lastTexture = textureNative(js.Null())
	c.lastFramebuffer = framebufferNative(js.Null())
	c.lastViewportWidth = 0
	c.lastViewportHeight = 0
	c.lastCompositeMode = driver.CompositeModeUnknown

	c.gl = js.Value{}
	c.ensureGL()
	if c.gl.Call("isContextLost").Bool() {
		return driver.GraphicsNotReady
	}
	gl := c.gl
	gl.Call("enable", blend)
	c.blendFunc(driver.CompositeModeSourceOver)
	f := gl.Call("getParameter", framebufferBinding)
	c.screenFramebuffer = framebufferNative(f)
	return nil
}

func (c *context) blendFunc(mode driver.CompositeMode) {
	if c.lastCompositeMode == mode {
		return
	}
	c.lastCompositeMode = mode
	s, d := mode.Operations()
	s2, d2 := convertOperation(s), convertOperation(d)
	c.ensureGL()
	gl := c.gl
	gl.Call("blendFunc", int(s2), int(d2))
}

func (c *context) newTexture(width, height int) (textureNative, error) {
	c.ensureGL()
	gl := c.gl
	t := gl.Call("createTexture")
	if jsutil.Equal(t, js.Null()) {
		return textureNative(js.Null()), errors.New("opengl: glGenTexture failed")
	}
	gl.Call("pixelStorei", unpackAlignment, 4)
	c.bindTexture(textureNative(t))

	gl.Call("texParameteri", texture2d, textureMagFilter, nearest)
	gl.Call("texParameteri", texture2d, textureMinFilter, nearest)
	gl.Call("texParameteri", texture2d, textureWrapS, clampToEdge)
	gl.Call("texParameteri", texture2d, textureWrapT, clampToEdge)

	// Firefox warns the usage of textures without specifying pixels (#629)
	//
	//     Error: WebGL warning: drawElements: This operation requires zeroing texture data. This is slow.
	//
	// In Ebiten, textures are filled with pixels laster by the filter that ignores destination, so it is fine
	// to leave textures as uninitialized here. Rather, extra memory allocating for initialization should be
	// avoided.
	gl.Call("texImage2D", texture2d, 0, rgba, width, height, 0, rgba, unsignedByte, nil)

	return textureNative(t), nil
}

func (c *context) bindFramebufferImpl(f framebufferNative) {
	c.ensureGL()
	gl := c.gl
	gl.Call("bindFramebuffer", framebuffer_, js.Value(f))
}

func (c *context) framebufferPixels(f *framebuffer, width, height int) ([]byte, error) {
	c.ensureGL()
	gl := c.gl

	c.bindFramebuffer(f.native)

	p := jsutil.TemporaryUint8Array(4 * width * height)
	gl.Call("readPixels", 0, 0, width, height, rgba, unsignedByte, p)

	return jsutil.Uint8ArrayToSlice(p), nil
}

func (c *context) activeTexture(idx int) {
	c.ensureGL()
	gl := c.gl
	gl.Call("activeTexture", texture0+idx)
}

func (c *context) bindTextureImpl(t textureNative) {
	c.ensureGL()
	gl := c.gl
	gl.Call("bindTexture", texture2d, js.Value(t))
}

func (c *context) deleteTexture(t textureNative) {
	c.ensureGL()
	gl := c.gl
	if !gl.Call("isTexture", js.Value(t)).Bool() {
		return
	}
	if c.lastTexture.equal(t) {
		c.lastTexture = textureNative(js.Null())
	}
	gl.Call("deleteTexture", js.Value(t))
}

func (c *context) isTexture(t textureNative) bool {
	c.ensureGL()
	gl := c.gl
	return gl.Call("isTexture", js.Value(t)).Bool()
}

func (c *context) newFramebuffer(t textureNative) (framebufferNative, error) {
	c.ensureGL()
	gl := c.gl
	f := gl.Call("createFramebuffer")
	c.bindFramebuffer(framebufferNative(f))

	gl.Call("framebufferTexture2D", framebuffer_, colorAttachment0, texture2d, js.Value(t), 0)
	if s := gl.Call("checkFramebufferStatus", framebuffer_); s.Int() != framebufferComplete.Int() {
		return framebufferNative(js.Null()), errors.New(fmt.Sprintf("opengl: creating framebuffer failed: %d", s.Int()))
	}

	return framebufferNative(f), nil
}

func (c *context) setViewportImpl(width, height int) {
	c.ensureGL()
	gl := c.gl
	gl.Call("viewport", 0, 0, width, height)
}

func (c *context) deleteFramebuffer(f framebufferNative) {
	c.ensureGL()
	gl := c.gl
	if !gl.Call("isFramebuffer", js.Value(f)).Bool() {
		return
	}
	// If a framebuffer to be deleted is bound, a newly bound framebuffer
	// will be a default framebuffer.
	// https://www.khronos.org/opengles/sdk/docs/man/xhtml/glDeleteFramebuffers.xml
	if c.lastFramebuffer.equal(f) {
		c.lastFramebuffer = framebufferNative(js.Null())
		c.lastViewportWidth = 0
		c.lastViewportHeight = 0
	}
	gl.Call("deleteFramebuffer", js.Value(f))
}

func (c *context) newShader(shaderType shaderType, source string) (shader, error) {
	c.ensureGL()
	gl := c.gl
	s := gl.Call("createShader", int(shaderType))
	if jsutil.Equal(s, js.Null()) {
		return shader(js.Null()), fmt.Errorf("opengl: glCreateShader failed: shader type: %d", shaderType)
	}

	gl.Call("shaderSource", js.Value(s), source)
	gl.Call("compileShader", js.Value(s))

	if !gl.Call("getShaderParameter", js.Value(s), compileStatus).Bool() {
		log := gl.Call("getShaderInfoLog", js.Value(s))
		return shader(js.Null()), fmt.Errorf("opengl: shader compile failed: %s", log)
	}
	return shader(s), nil
}

func (c *context) deleteShader(s shader) {
	c.ensureGL()
	gl := c.gl
	gl.Call("deleteShader", js.Value(s))
}

func (c *context) newProgram(shaders []shader, attributes []string) (program, error) {
	c.ensureGL()
	gl := c.gl
	v := gl.Call("createProgram")
	if jsutil.Equal(v, js.Null()) {
		return program{}, errors.New("opengl: glCreateProgram failed")
	}

	for _, shader := range shaders {
		gl.Call("attachShader", v, js.Value(shader))
	}

	for i, name := range attributes {
		gl.Call("bindAttribLocation", v, i, name)
	}

	gl.Call("linkProgram", v)
	if !gl.Call("getProgramParameter", v, linkStatus).Bool() {
		return program{}, errors.New("opengl: program error")
	}

	id := c.lastProgramID
	c.lastProgramID++
	return program{
		value: v,
		id:    id,
	}, nil
}

func (c *context) useProgram(p program) {
	c.ensureGL()
	gl := c.gl
	gl.Call("useProgram", p.value)
}

func (c *context) deleteProgram(p program) {
	c.ensureGL()
	gl := c.gl
	if !gl.Call("isProgram", p.value).Bool() {
		return
	}
	gl.Call("deleteProgram", p.value)
}

func (c *context) getUniformLocationImpl(p program, location string) uniformLocation {
	c.ensureGL()
	gl := c.gl
	return uniformLocation(gl.Call("getUniformLocation", p.value, location))
}

func (c *context) uniformInt(p program, location string, v int) {
	c.ensureGL()
	gl := c.gl
	l := c.locationCache.GetUniformLocation(c, p, location)
	gl.Call("uniform1i", js.Value(l), v)
}

func (c *context) uniformFloat(p program, location string, v float32) {
	c.ensureGL()
	gl := c.gl
	l := c.locationCache.GetUniformLocation(c, p, location)
	gl.Call("uniform1f", js.Value(l), v)
}

func (c *context) uniformFloats(p program, location string, v []float32) {
	c.ensureGL()
	gl := c.gl
	l := c.locationCache.GetUniformLocation(c, p, location)
	switch len(v) {
	case 2:
		gl.Call("uniform2f", js.Value(l), v[0], v[1])
	case 4:
		gl.Call("uniform4f", js.Value(l), v[0], v[1], v[2], v[3])
	case 16:
		arr8 := jsutil.TemporaryUint8Array(len(v) * 4)
		arr := js.Global().Get("Float32Array").New(arr8.Get("buffer"), arr8.Get("byteOffset"), len(v))
		jsutil.CopySliceToJS(arr, v)
		gl.Call("uniformMatrix4fv", js.Value(l), false, arr)
	default:
		panic(fmt.Sprintf("opengl: invalid uniform floats num: %d", len(v)))
	}
}

func (c *context) vertexAttribPointer(p program, index int, size int, dataType dataType, stride int, offset int) {
	c.ensureGL()
	gl := c.gl
	gl.Call("vertexAttribPointer", index, size, int(dataType), false, stride, offset)
}

func (c *context) enableVertexAttribArray(p program, index int) {
	c.ensureGL()
	gl := c.gl
	gl.Call("enableVertexAttribArray", index)
}

func (c *context) disableVertexAttribArray(p program, index int) {
	c.ensureGL()
	gl := c.gl
	gl.Call("disableVertexAttribArray", index)
}

func (c *context) newArrayBuffer(size int) buffer {
	c.ensureGL()
	gl := c.gl
	b := gl.Call("createBuffer")
	gl.Call("bindBuffer", int(arrayBuffer), js.Value(b))
	gl.Call("bufferData", int(arrayBuffer), size, int(dynamicDraw))
	return buffer(b)
}

func (c *context) newElementArrayBuffer(size int) buffer {
	c.ensureGL()
	gl := c.gl
	b := gl.Call("createBuffer")
	gl.Call("bindBuffer", int(elementArrayBuffer), js.Value(b))
	gl.Call("bufferData", int(elementArrayBuffer), size, int(dynamicDraw))
	return buffer(b)
}

func (c *context) bindBuffer(bufferType bufferType, b buffer) {
	c.ensureGL()
	gl := c.gl
	gl.Call("bindBuffer", int(bufferType), js.Value(b))
}

func (c *context) arrayBufferSubData(data []float32) {
	c.ensureGL()
	gl := c.gl
	arr8 := jsutil.TemporaryUint8Array(len(data) * 4)
	arr := js.Global().Get("Float32Array").New(arr8.Get("buffer"), arr8.Get("byteOffset"), len(data))
	jsutil.CopySliceToJS(arr, data)
	gl.Call("bufferSubData", int(arrayBuffer), 0, arr)
}

func (c *context) elementArrayBufferSubData(data []uint16) {
	c.ensureGL()
	gl := c.gl
	arr8 := jsutil.TemporaryUint8Array(len(data) * 2)
	arr := js.Global().Get("Uint16Array").New(arr8.Get("buffer"), arr8.Get("byteOffset"), len(data))
	jsutil.CopySliceToJS(arr, data)
	gl.Call("bufferSubData", int(elementArrayBuffer), 0, arr)
}

func (c *context) deleteBuffer(b buffer) {
	c.ensureGL()
	gl := c.gl
	gl.Call("deleteBuffer", js.Value(b))
}

func (c *context) drawElements(len int, offsetInBytes int) {
	c.ensureGL()
	gl := c.gl
	gl.Call("drawElements", triangles, len, unsignedShort, offsetInBytes)
}

func (c *context) maxTextureSizeImpl() int {
	c.ensureGL()
	gl := c.gl
	return gl.Call("getParameter", maxTextureSize).Int()
}

func (c *context) getShaderPrecisionFormatPrecision() int {
	c.ensureGL()
	gl := c.gl
	return gl.Call("getShaderPrecisionFormat", js.ValueOf(int(fragmentShader)), highFloat).Get("precision").Int()
}

func (c *context) flush() {
	c.ensureGL()
	gl := c.gl
	gl.Call("flush")
}

func (c *context) needsRestoring() bool {
	return !web.IsMobileBrowser()
}

func (c *context) canUsePBO() bool {
	return isWebGL2Available
}

func (c *context) texSubImage2D(t textureNative, width, height int, args []*driver.ReplacePixelsArgs) {
	c.ensureGL()
	c.bindTexture(t)
	gl := c.gl
	// void texSubImage2D(GLenum target, GLint level, GLint xoffset, GLint yoffset,
	//                    GLsizei width, GLsizei height,
	//                    GLenum format, GLenum type, ArrayBufferView? pixels);
	for _, a := range args {
		arr := jsutil.TemporaryUint8Array(len(a.Pixels))
		jsutil.CopySliceToJS(arr, a.Pixels)
		gl.Call("texSubImage2D", texture2d, 0, a.X, a.Y, a.Width, a.Height, rgba, unsignedByte, arr)
	}
}

func (c *context) newPixelBufferObject(width, height int) buffer {
	c.ensureGL()
	gl := c.gl
	b := gl.Call("createBuffer")
	gl.Call("bindBuffer", int(pixelUnpackBuffer), js.Value(b))
	gl.Call("bufferData", int(pixelUnpackBuffer), 4*width*height, int(streamDraw))
	gl.Call("bindBuffer", int(pixelUnpackBuffer), nil)
	return buffer(b)
}

func (c *context) replacePixelsWithPBO(buffer buffer, t textureNative, width, height int, args []*driver.ReplacePixelsArgs) {
	c.ensureGL()
	c.bindTexture(t)
	gl := c.gl
	gl.Call("bindBuffer", int(pixelUnpackBuffer), js.Value(buffer))

	stride := 4 * width
	for _, a := range args {
		arr := jsutil.TemporaryUint8Array(len(a.Pixels))
		jsutil.CopySliceToJS(arr, a.Pixels)
		offset := 4 * (a.Y*width + a.X)
		for j := 0; j < a.Height; j++ {
			gl.Call("bufferSubData", int(pixelUnpackBuffer), offset+stride*j, arr, 4*a.Width*j, 4*a.Width)
		}
	}

	// void texSubImage2D(GLenum target, GLint level, GLint xoffset, GLint yoffset,
	//                    GLsizei width, GLsizei height,
	//                    GLenum format, GLenum type, GLintptr offset);
	gl.Call("texSubImage2D", texture2d, 0, 0, 0, width, height, rgba, unsignedByte, 0)
	gl.Call("bindBuffer", int(pixelUnpackBuffer), nil)
}