// 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"

	"github.com/gopherjs/gopherwasm/js"

	"github.com/hajimehoshi/ebiten/internal/graphics"
)

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
	}
)

var InvalidTexture = textureNative(js.Null())

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

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

func init() {
	// Accessing the prototype is rquired on Safari.
	c := js.Global().Get("WebGLRenderingContext").Get("prototype")
	vertexShader = shaderType(c.Get("VERTEX_SHADER").Int())
	fragmentShader = shaderType(c.Get("FRAGMENT_SHADER").Int())
	arrayBuffer = bufferType(c.Get("ARRAY_BUFFER").Int())
	elementArrayBuffer = bufferType(c.Get("ELEMENT_ARRAY_BUFFER").Int())
	dynamicDraw = bufferUsage(c.Get("DYNAMIC_DRAW").Int())
	short = dataType(c.Get("SHORT").Int())
	float = dataType(c.Get("FLOAT").Int())

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

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

type contextImpl struct {
	gl            js.Value
	loseContext   js.Value
	lastProgramID programID
}

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

	if js.Global().Get("WebGLRenderingContext") == js.Undefined() {
		panic("opengl: WebGL is not supported")
	}
	// 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)
	gl := canvas.Call("getContext", "webgl", attr)
	if gl == js.Null() {
		gl = canvas.Call("getContext", "experimental-webgl", attr)
		if gl == js.Null() {
			panic("opengl: getContext failed")
		}
	}

	c.gl = gl

	// Getting an extension might fail after the context is lost, so
	// it is required to get the extension here.
	c.loseContext = gl.Call("getExtension", "WEBGL_lose_context")
}

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 = graphics.CompositeModeUnknown

	c.ensureGL()
	gl := c.gl
	gl.Call("enable", blend)
	c.blendFunc(graphics.CompositeModeSourceOver)
	f := gl.Call("getParameter", framebufferBinding)
	c.screenFramebuffer = framebufferNative(f)
	return nil
}

func (c *context) blendFunc(mode graphics.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 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)

	pixels := make([]byte, 4*width*height)
	p := js.TypedArrayOf(pixels)
	gl.Call("readPixels", 0, 0, width, height, rgba, unsignedByte, p)
	p.Release()

	if e := gl.Call("getError"); e.Int() != noError.Int() {
		return nil, errors.New(fmt.Sprintf("opengl: error: %d", e))
	}
	return pixels, nil
}

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 == 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) texSubImage2D(t textureNative, pixels []byte, x, y, width, height int) {
	c.bindTexture(t)
	c.ensureGL()
	gl := c.gl
	// void texSubImage2D(GLenum target, GLint level, GLint xoffset, GLint yoffset,
	//                    GLsizei width, GLsizei height,
	//                    GLenum format, GLenum type, ArrayBufferView? pixels);
	p := js.TypedArrayOf(pixels)
	gl.Call("texSubImage2D", texture2d, 0, x, y, width, height, rgba, unsignedByte, p)
	p.Release()
}

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 == 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 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) (program, error) {
	c.ensureGL()
	gl := c.gl
	v := gl.Call("createProgram")
	if v == js.Null() {
		return program{}, errors.New("opengl: glCreateProgram failed")
	}

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

var (
	float32Array = js.Global().Get("Float32Array")
)

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:
		arr := js.TypedArrayOf(v)
		gl.Call("uniformMatrix4fv", js.Value(l), false, arr)
		arr.Release()
	default:
		panic("not reached")
	}
}

func (c *context) getAttribLocationImpl(p program, location string) attribLocation {
	c.ensureGL()
	gl := c.gl
	return attribLocation(gl.Call("getAttribLocation", p.value, location).Int())
}

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

func (c *context) enableVertexAttribArray(p program, location string) {
	c.ensureGL()
	gl := c.gl
	l := c.locationCache.GetAttribLocation(c, p, location)
	gl.Call("enableVertexAttribArray", int(l))
}

func (c *context) disableVertexAttribArray(p program, location string) {
	c.ensureGL()
	gl := c.gl
	l := c.locationCache.GetAttribLocation(c, p, location)
	gl.Call("disableVertexAttribArray", int(l))
}

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
	arr := js.TypedArrayOf(data)
	gl.Call("bufferSubData", int(arrayBuffer), 0, arr)
	arr.Release()
}

func (c *context) elementArrayBufferSubData(data []uint16) {
	c.ensureGL()
	gl := c.gl
	arr := js.TypedArrayOf(data)
	gl.Call("bufferSubData", int(elementArrayBuffer), 0, arr)
	arr.Release()
}

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

func (c *context) isContextLost() bool {
	c.ensureGL()
	gl := c.gl
	return gl.Call("isContextLost").Bool()
}

func (c *context) restoreContext() {
	if c.loseContext != js.Null() {
		c.loseContext.Call("restoreContext")
	}
}