// 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 darwin linux windows
// +build !js
// +build !android

package opengl

import (
	"errors"
	"fmt"

	"github.com/go-gl/gl/v2.1/gl"
)

type Texture uint32
type Framebuffer uint32
type Shader uint32
type Program uint32
type Buffer uint32

var ZeroFramebuffer Framebuffer

type uniformLocation int32
type attribLocation int32

type programID uint32

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

type context struct {
	funcs chan func()
}

func NewContext() (*Context, error) {
	c := &Context{
		Nearest:            gl.NEAREST,
		Linear:             gl.LINEAR,
		VertexShader:       gl.VERTEX_SHADER,
		FragmentShader:     gl.FRAGMENT_SHADER,
		ArrayBuffer:        gl.ARRAY_BUFFER,
		ElementArrayBuffer: gl.ELEMENT_ARRAY_BUFFER,
		DynamicDraw:        gl.DYNAMIC_DRAW,
		StaticDraw:         gl.STATIC_DRAW,
		Triangles:          gl.TRIANGLES,
		Lines:              gl.LINES,
		zero:               gl.ZERO,
		one:                gl.ONE,
		srcAlpha:           gl.SRC_ALPHA,
		dstAlpha:           gl.DST_ALPHA,
		oneMinusSrcAlpha:   gl.ONE_MINUS_SRC_ALPHA,
		oneMinusDstAlpha:   gl.ONE_MINUS_DST_ALPHA,
		locationCache:      newLocationCache(),
		lastCompositeMode:  CompositeModeUnknown,
	}
	c.funcs = make(chan func())
	return c, nil
}

func (c *Context) Loop() {
	for f := range c.funcs {
		f()
	}
}

func (c *Context) RunOnContextThread(f func() error) error {
	ch := make(chan struct{})
	var err error
	c.funcs <- func() {
		err = f()
		close(ch)
	}
	<-ch
	return err
}

func (c *Context) Init() error {
	if err := c.RunOnContextThread(func() error {
		// This initialization must be done after Loop is called.
		// This is why Init is separated from NewContext.

		if err := gl.Init(); err != nil {
			return fmt.Errorf("opengl: initializing error %v", err)
		}
		// Textures' pixel formats are alpha premultiplied.
		gl.Enable(gl.BLEND)
		return nil
	}); err != nil {
		return err
	}
	c.BlendFunc(CompositeModeSourceOver)
	return nil
}

func (c *Context) BlendFunc(mode CompositeMode) {
	c.RunOnContextThread(func() error {
		if c.lastCompositeMode == mode {
			return nil
		}
		c.lastCompositeMode = mode
		s, d := c.operations(mode)
		gl.BlendFunc(uint32(s), uint32(d))
		return nil
	})
}

func (c *Context) NewTexture(width, height int, pixels []uint8, filter Filter) (Texture, error) {
	var texture Texture
	if err := c.RunOnContextThread(func() error {
		var t uint32
		gl.GenTextures(1, &t)
		// TOOD: Use gl.IsTexture
		if t <= 0 {
			return errors.New("opengl: creating texture failed")
		}
		gl.PixelStorei(gl.UNPACK_ALIGNMENT, 4)
		gl.BindTexture(gl.TEXTURE_2D, t)

		gl.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, int32(filter))
		gl.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, int32(filter))

		var p interface{}
		if pixels != nil {
			p = pixels
		}
		gl.TexImage2D(gl.TEXTURE_2D, 0, gl.RGBA, int32(width), int32(height), 0, gl.RGBA, gl.UNSIGNED_BYTE, gl.Ptr(p))

		texture = Texture(t)
		return nil
	}); err != nil {
		return 0, err
	}
	return texture, nil
}

func (c *Context) bindFramebufferImpl(f Framebuffer) {
	gl.BindFramebuffer(gl.FRAMEBUFFER, uint32(f))
}

func (c *Context) FramebufferPixels(f Framebuffer, width, height int) ([]uint8, error) {
	var pixels []uint8
	if err := c.RunOnContextThread(func() error {
		gl.Flush()
		c.bindFramebuffer(f)
		pixels = make([]uint8, 4*width*height)
		gl.ReadPixels(0, 0, int32(width), int32(height), gl.RGBA, gl.UNSIGNED_BYTE, gl.Ptr(pixels))
		if e := gl.GetError(); e != gl.NO_ERROR {
			pixels = nil
			return fmt.Errorf("opengl: glReadPixels: %d", e)
		}
		return nil
	}); err != nil {
		return nil, err
	}
	return pixels, nil
}

func (c *Context) BindTexture(t Texture) {
	c.RunOnContextThread(func() error {
		gl.BindTexture(gl.TEXTURE_2D, uint32(t))
		return nil
	})
}

func (c *Context) DeleteTexture(t Texture) {
	c.RunOnContextThread(func() error {
		tt := uint32(t)
		gl.DeleteTextures(1, &tt)
		return nil
	})
}

func (c *Context) TexSubImage2D(p []uint8, width, height int) {
	c.RunOnContextThread(func() error {
		gl.TexSubImage2D(gl.TEXTURE_2D, 0, 0, 0, int32(width), int32(height), gl.RGBA, gl.UNSIGNED_BYTE, gl.Ptr(p))
		return nil
	})
}

func (c *Context) BindZeroFramebuffer() {
	c.RunOnContextThread(func() error {
		c.bindFramebuffer(ZeroFramebuffer)
		return nil
	})
}

func (c *Context) NewFramebuffer(texture Texture) (Framebuffer, error) {
	var framebuffer Framebuffer
	if err := c.RunOnContextThread(func() error {
		var f uint32
		gl.GenFramebuffers(1, &f)
		// TODO: Use gl.IsFramebuffer
		if f <= 0 {
			return errors.New("opengl: creating framebuffer failed: gl.IsFramebuffer returns false")
		}
		c.bindFramebuffer(Framebuffer(f))

		gl.FramebufferTexture2D(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0, gl.TEXTURE_2D, uint32(texture), 0)
		s := gl.CheckFramebufferStatus(gl.FRAMEBUFFER)
		if s != gl.FRAMEBUFFER_COMPLETE {
			if s != 0 {
				return fmt.Errorf("opengl: creating framebuffer failed: %v", s)
			}
			if e := gl.GetError(); e != gl.NO_ERROR {
				return fmt.Errorf("opengl: creating framebuffer failed: (glGetError) %d", e)
			}
			return fmt.Errorf("opengl: creating framebuffer failed: unknown error")
		}
		framebuffer = Framebuffer(f)
		return nil
	}); err != nil {
		return 0, err
	}
	return framebuffer, nil
}

func (c *Context) SetViewport(f Framebuffer, width, height int) error {
	return c.RunOnContextThread(func() error {
		c.bindFramebuffer(f)
		gl.Viewport(0, 0, int32(width), int32(height))
		return nil
	})
}

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

func (c *Context) DeleteFramebuffer(f Framebuffer) {
	c.RunOnContextThread(func() error {
		ff := uint32(f)
		// 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.DeleteFramebuffers(1, &ff)
		return nil
	})
}

func (c *Context) NewShader(shaderType ShaderType, source string) (Shader, error) {
	var shader Shader
	if err := c.RunOnContextThread(func() error {
		s := gl.CreateShader(uint32(shaderType))
		if s == 0 {
			return errors.New("opengl: glCreateShader failed")
		}
		cSources, free := gl.Strs(source + "\x00")
		gl.ShaderSource(uint32(s), 1, cSources, nil)
		free()
		gl.CompileShader(s)

		var v int32
		gl.GetShaderiv(s, gl.COMPILE_STATUS, &v)
		if v == gl.FALSE {
			log := []uint8{}
			gl.GetShaderiv(uint32(s), gl.INFO_LOG_LENGTH, &v)
			if v != 0 {
				log = make([]uint8, int(v))
				gl.GetShaderInfoLog(uint32(s), v, nil, (*uint8)(gl.Ptr(log)))
			}
			return fmt.Errorf("opengl: shader compile failed: %s", log)
		}
		shader = Shader(s)
		return nil
	}); err != nil {
		return 0, err
	}
	return shader, nil
}

func (c *Context) DeleteShader(s Shader) {
	c.RunOnContextThread(func() error {
		gl.DeleteShader(uint32(s))
		return nil
	})
}

func (c *Context) GlslHighpSupported() bool {
	return false
}

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

		for _, shader := range shaders {
			gl.AttachShader(p, uint32(shader))
		}
		gl.LinkProgram(p)
		var v int32
		gl.GetProgramiv(p, gl.LINK_STATUS, &v)
		if v == gl.FALSE {
			return errors.New("opengl: program error")
		}
		program = Program(p)
		return nil
	}); err != nil {
		return 0, err
	}
	return program, nil
}

func (c *Context) UseProgram(p Program) {
	c.RunOnContextThread(func() error {
		gl.UseProgram(uint32(p))
		return nil
	})
}

func (c *Context) getUniformLocation(p Program, location string) uniformLocation {
	uniform := uniformLocation(gl.GetUniformLocation(uint32(p), gl.Str(location+"\x00")))
	if uniform == -1 {
		panic("opengl: invalid uniform location: " + location)
	}
	return uniform
}

func (c *Context) UniformInt(p Program, location string, v int) {
	c.RunOnContextThread(func() error {
		l := int32(c.locationCache.GetUniformLocation(c, p, location))
		gl.Uniform1i(l, int32(v))
		return nil
	})
}

func (c *Context) UniformFloats(p Program, location string, v []float32) {
	c.RunOnContextThread(func() error {
		l := int32(c.locationCache.GetUniformLocation(c, p, location))
		switch len(v) {
		case 4:
			gl.Uniform4fv(l, 1, (*float32)(gl.Ptr(v)))
		case 16:
			gl.UniformMatrix4fv(l, 1, false, (*float32)(gl.Ptr(v)))
		default:
			panic("not reach")
		}
		return nil
	})
}

func (c *Context) getAttribLocation(p Program, location string) attribLocation {
	attrib := attribLocation(gl.GetAttribLocation(uint32(p), gl.Str(location+"\x00")))
	if attrib == -1 {
		panic("opengl: invalid attrib location: " + location)
	}
	return attrib
}

func (c *Context) VertexAttribPointer(p Program, location string, normalize bool, stride int, size int, v int) {
	c.RunOnContextThread(func() error {
		l := c.locationCache.GetAttribLocation(c, p, location)
		gl.VertexAttribPointer(uint32(l), int32(size), gl.SHORT, normalize, int32(stride), gl.PtrOffset(v))
		return nil
	})
}

func (c *Context) EnableVertexAttribArray(p Program, location string) {
	c.RunOnContextThread(func() error {
		l := c.locationCache.GetAttribLocation(c, p, location)
		gl.EnableVertexAttribArray(uint32(l))
		return nil
	})
}

func (c *Context) DisableVertexAttribArray(p Program, location string) {
	c.RunOnContextThread(func() error {
		l := c.locationCache.GetAttribLocation(c, p, location)
		gl.DisableVertexAttribArray(uint32(l))
		return nil
	})
}

func (c *Context) DeleteProgram(p Program) {
	c.RunOnContextThread(func() error {
		gl.DeleteProgram(uint32(p))
		return nil
	})
}

func (c *Context) NewBuffer(bufferType BufferType, v interface{}, bufferUsage BufferUsage) Buffer {
	var buffer Buffer
	c.RunOnContextThread(func() error {
		var b uint32
		gl.GenBuffers(1, &b)
		gl.BindBuffer(uint32(bufferType), b)
		switch v := v.(type) {
		case int:
			gl.BufferData(uint32(bufferType), v, nil, uint32(bufferUsage))
		case []uint16:
			gl.BufferData(uint32(bufferType), 2*len(v), gl.Ptr(v), uint32(bufferUsage))
		default:
			panic("not reach")
		}
		buffer = Buffer(b)
		return nil
	})
	return buffer
}

func (c *Context) BindElementArrayBuffer(b Buffer) {
	c.RunOnContextThread(func() error {
		gl.BindBuffer(gl.ELEMENT_ARRAY_BUFFER, uint32(b))
		return nil
	})
}

func (c *Context) BufferSubData(bufferType BufferType, data []int16) {
	c.RunOnContextThread(func() error {
		gl.BufferSubData(uint32(bufferType), 0, 2*len(data), gl.Ptr(data))
		return nil
	})
}

func (c *Context) DeleteBuffer(b Buffer) {
	c.RunOnContextThread(func() error {
		bb := uint32(b)
		gl.DeleteBuffers(1, &bb)
		return nil
	})
}

func (c *Context) DrawElements(mode Mode, len int, offsetInBytes int) {
	c.RunOnContextThread(func() error {
		gl.DrawElements(uint32(mode), int32(len), gl.UNSIGNED_SHORT, gl.PtrOffset(offsetInBytes))
		return nil
	})
}