// 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 android

package opengl

import (
	"errors"
	"fmt"

	mgl "golang.org/x/mobile/gl"
)

type Texture mgl.Texture
type Framebuffer mgl.Framebuffer
type Shader mgl.Shader
type Program mgl.Program
type Buffer mgl.Buffer

var ZeroFramebuffer Framebuffer

type uniformLocation mgl.Uniform
type attribLocation mgl.Attrib

type programID uint32

func (p Program) id() programID {
	return programID(p.Value)
}

type context struct {
	gl          mgl.Context
	worker      mgl.Worker
	initialized chan struct{}
}

func NewContext() (*Context, error) {
	c := &Context{
		Nearest:            mgl.NEAREST,
		Linear:             mgl.LINEAR,
		VertexShader:       mgl.VERTEX_SHADER,
		FragmentShader:     mgl.FRAGMENT_SHADER,
		ArrayBuffer:        mgl.ARRAY_BUFFER,
		ElementArrayBuffer: mgl.ELEMENT_ARRAY_BUFFER,
		DynamicDraw:        mgl.DYNAMIC_DRAW,
		StaticDraw:         mgl.STATIC_DRAW,
		Triangles:          mgl.TRIANGLES,
		Lines:              mgl.LINES,
		zero:               mgl.ZERO,
		one:                mgl.ONE,
		srcAlpha:           mgl.SRC_ALPHA,
		dstAlpha:           mgl.DST_ALPHA,
		oneMinusSrcAlpha:   mgl.ONE_MINUS_SRC_ALPHA,
		oneMinusDstAlpha:   mgl.ONE_MINUS_DST_ALPHA,
		locationCache:      newLocationCache(),
		lastCompositeMode:  CompositeModeUnknown,
	}
	c.gl, c.worker = mgl.NewContext()
	c.initialized = make(chan struct{})
	go func() {
		// GL calls will just enqueue an task to the worker.
		// Since the worker is not avaialbe, this enqueuing should be done
		// in a goroutine.

		// Textures' pixel formats are alpha premultiplied.
		c.gl.Enable(mgl.BLEND)
		c.BlendFunc(CompositeModeSourceOver)
		close(c.initialized)
	}()
	return c, nil
}

func (c *Context) WaitUntilInitializingDone() {
	// TODO: Call this function at an approriate place
	<-c.initialized
}

func (c *Context) Worker() mgl.Worker {
	return c.worker
}

func (c *Context) BlendFunc(mode CompositeMode) {
	gl := c.gl
	if c.lastCompositeMode == mode {
		return
	}
	c.lastCompositeMode = mode
	s, d := c.operations(mode)
	gl.BlendFunc(mgl.Enum(s), mgl.Enum(d))
}

func (c *Context) NewTexture(width, height int, pixels []uint8, filter Filter) (Texture, error) {
	gl := c.gl
	t := gl.CreateTexture()
	if t.Value <= 0 {
		return Texture{}, errors.New("opengl: creating texture failed")
	}
	gl.PixelStorei(mgl.UNPACK_ALIGNMENT, 4)
	gl.BindTexture(mgl.TEXTURE_2D, t)

	gl.TexParameteri(mgl.TEXTURE_2D, mgl.TEXTURE_MAG_FILTER, int(filter))
	gl.TexParameteri(mgl.TEXTURE_2D, mgl.TEXTURE_MIN_FILTER, int(filter))

	var p []uint8
	if pixels != nil {
		p = pixels
	}
	gl.TexImage2D(mgl.TEXTURE_2D, 0, width, height, mgl.RGBA, mgl.UNSIGNED_BYTE, p)

	return Texture(t), nil
}

func (c *Context) bindFramebufferImpl(f Framebuffer) {
	gl := c.gl
	gl.BindFramebuffer(mgl.FRAMEBUFFER, mgl.Framebuffer(f))
}

func (c *Context) FramebufferPixels(f Framebuffer, width, height int) ([]uint8, error) {
	gl := c.gl
	gl.Flush()

	c.bindFramebuffer(f)

	pixels := make([]uint8, 4*width*height)
	gl.ReadPixels(pixels, 0, 0, width, height, mgl.RGBA, mgl.UNSIGNED_BYTE)
	if e := gl.GetError(); e != mgl.NO_ERROR {
		return nil, fmt.Errorf("opengl: glReadPixels: %d", e)
	}
	return pixels, nil
}

func (c *Context) BindTexture(t Texture) {
	gl := c.gl
	gl.BindTexture(mgl.TEXTURE_2D, mgl.Texture(t))
}

func (c *Context) DeleteTexture(t Texture) {
	gl := c.gl
	gl.DeleteTexture(mgl.Texture(t))
}

func (c *Context) TexSubImage2D(p []uint8, width, height int) {
	gl := c.gl
	gl.TexSubImage2D(mgl.TEXTURE_2D, 0, 0, 0, width, height, mgl.RGBA, mgl.UNSIGNED_BYTE, p)
}

func (c *Context) BindZeroFramebuffer() {
	c.bindFramebuffer(ZeroFramebuffer)
}

func (c *Context) NewFramebuffer(texture Texture) (Framebuffer, error) {
	gl := c.gl
	f := gl.CreateFramebuffer()
	if f.Value <= 0 {
		return Framebuffer{}, errors.New("opengl: creating framebuffer failed: gl.IsFramebuffer returns false")
	}
	c.bindFramebuffer(Framebuffer(f))

	gl.FramebufferTexture2D(mgl.FRAMEBUFFER, mgl.COLOR_ATTACHMENT0, mgl.TEXTURE_2D, mgl.Texture(texture), 0)
	s := gl.CheckFramebufferStatus(mgl.FRAMEBUFFER)
	if s != mgl.FRAMEBUFFER_COMPLETE {
		if s != 0 {
			return Framebuffer{}, fmt.Errorf("opengl: creating framebuffer failed: %v", s)
		}
		if e := gl.GetError(); e != mgl.NO_ERROR {
			return Framebuffer{}, fmt.Errorf("opengl: creating framebuffer failed: (glGetError) %d", e)
		}
		return Framebuffer{}, fmt.Errorf("opengl: creating framebuffer failed: unknown error")
	}

	return Framebuffer(f), nil
}

func (c *Context) SetViewport(f Framebuffer, width, height int) error {
	gl := c.gl
	c.bindFramebuffer(f)
	gl.Viewport(0, 0, width, height)
	return nil
}

func (c *Context) FillFramebuffer(r, g, b, a float64) error {
	gl := c.gl
	gl.ClearColor(float32(r), float32(g), float32(b), float32(a))
	gl.Clear(mgl.COLOR_BUFFER_BIT)
	return nil
}

func (c *Context) DeleteFramebuffer(f Framebuffer) {
	gl := c.gl
	// If a framebuffer to be delted 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 = ZeroFramebuffer
	}
	gl.DeleteFramebuffer(mgl.Framebuffer(f))
}

func (c *Context) NewShader(shaderType ShaderType, source string) (Shader, error) {
	gl := c.gl
	s := gl.CreateShader(mgl.Enum(shaderType))
	if s.Value == 0 {
		return Shader{}, errors.New("opengl: glCreateShader failed")
	}
	gl.ShaderSource(s, source)
	gl.CompileShader(s)

	v := gl.GetShaderi(s, mgl.COMPILE_STATUS)
	if v == mgl.FALSE {
		log := gl.GetShaderInfoLog(s)
		return Shader{}, fmt.Errorf("opengl: shader compile failed: %s", log)
	}
	return Shader(s), nil
}

func (c *Context) DeleteShader(s Shader) {
	gl := c.gl
	gl.DeleteShader(mgl.Shader(s))
}

func (c *Context) GlslHighpSupported() bool {
	// TODO: Fix this
	return false
}

func (c *Context) NewProgram(shaders []Shader) (Program, error) {
	gl := c.gl
	p := gl.CreateProgram()
	if p.Value == 0 {
		return Program{}, errors.New("opengl: glCreateProgram failed")
	}

	for _, shader := range shaders {
		gl.AttachShader(p, mgl.Shader(shader))
	}
	gl.LinkProgram(p)
	v := gl.GetProgrami(p, mgl.LINK_STATUS)
	if v == mgl.FALSE {
		return Program{}, errors.New("opengl: program error")
	}
	return Program(p), nil
}

func (c *Context) UseProgram(p Program) {
	gl := c.gl
	gl.UseProgram(mgl.Program(p))
}

func (c *Context) getUniformLocation(p Program, location string) uniformLocation {
	gl := c.gl
	u := uniformLocation(gl.GetUniformLocation(mgl.Program(p), location))
	if u.Value == -1 {
		panic("invalid uniform location: " + location)
	}
	return u
}

func (c *Context) UniformInt(p Program, location string, v int) {
	gl := c.gl
	gl.Uniform1i(mgl.Uniform(c.locationCache.GetUniformLocation(c, p, location)), v)
}

func (c *Context) UniformFloats(p Program, location string, v []float32) {
	gl := c.gl
	l := mgl.Uniform(c.locationCache.GetUniformLocation(c, p, location))
	switch len(v) {
	case 4:
		gl.Uniform4fv(l, v)
	case 16:
		gl.UniformMatrix4fv(l, v)
	default:
		panic("not reach")
	}
}

func (c *Context) getAttribLocation(p Program, location string) attribLocation {
	gl := c.gl
	a := attribLocation(gl.GetAttribLocation(mgl.Program(p), location))
	if a.Value == ^uint(0) {
		panic("invalid attrib location: " + location)
	}
	return a
}

func (c *Context) VertexAttribPointer(p Program, location string, normalize bool, stride int, size int, v int) {
	gl := c.gl
	l := c.locationCache.GetAttribLocation(c, p, location)
	gl.VertexAttribPointer(mgl.Attrib(l), size, mgl.SHORT, normalize, stride, v)
}

func (c *Context) EnableVertexAttribArray(p Program, location string) {
	gl := c.gl
	l := c.locationCache.GetAttribLocation(c, p, location)
	gl.EnableVertexAttribArray(mgl.Attrib(l))
}

func (c *Context) DisableVertexAttribArray(p Program, location string) {
	gl := c.gl
	l := c.locationCache.GetAttribLocation(c, p, location)
	gl.DisableVertexAttribArray(mgl.Attrib(l))
}

func (c *Context) DeleteProgram(p Program) {
	gl := c.gl
	gl.DeleteProgram(mgl.Program(p))
}

func uint16ToBytes(v []uint16) []byte {
	b := make([]byte, len(v)*2)
	for i, x := range v {
		b[2*i] = byte(x)
		b[2*i+1] = byte(x >> 8)
	}
	return b
}

func int16ToBytes(v []int16) []byte {
	b := make([]byte, len(v)*2)
	for i, x := range v {
		b[2*i] = byte(uint16(x))
		b[2*i+1] = byte(uint16(x) >> 8)
	}
	return b
}

func (c *Context) NewBuffer(bufferType BufferType, v interface{}, bufferUsage BufferUsage) Buffer {
	gl := c.gl
	b := gl.CreateBuffer()
	gl.BindBuffer(mgl.Enum(bufferType), b)
	switch v := v.(type) {
	case int:
		gl.BufferInit(mgl.Enum(bufferType), v, mgl.Enum(bufferUsage))
	case []uint16:
		gl.BufferData(mgl.Enum(bufferType), uint16ToBytes(v), mgl.Enum(bufferUsage))
	default:
		panic("not reach")
	}
	return Buffer(b)
}

func (c *Context) BindElementArrayBuffer(b Buffer) {
	gl := c.gl
	gl.BindBuffer(mgl.ELEMENT_ARRAY_BUFFER, mgl.Buffer(b))
}

func (c *Context) BufferSubData(bufferType BufferType, data []int16) {
	gl := c.gl
	gl.BufferSubData(mgl.Enum(bufferType), 0, int16ToBytes(data))
}

func (c *Context) DeleteBuffer(b Buffer) {
	gl := c.gl
	gl.DeleteBuffer(mgl.Buffer(b))
}

func (c *Context) DrawElements(mode Mode, len int, offsetInBytes int) {
	gl := c.gl
	gl.DrawElements(mgl.Enum(mode), len, mgl.UNSIGNED_SHORT, offsetInBytes)
}