// 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.

package graphics

import (
	"fmt"

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

type openGLState struct {
	initialized          bool
	indexBufferLines     opengl.Buffer
	indexBufferQuads     opengl.Buffer
	programTexture       opengl.Program
	lastProgram          opengl.Program
	lastProjectionMatrix []float32
	lastModelviewMatrix  []float32
	lastColorMatrix      []float32
}

var theOpenGLState openGLState

const (
	indicesNum = 1 << 16
	MaxQuads   = indicesNum / 6
)

// unsafe.SizeOf can't be used because unsafe doesn't work with GopherJS.
const (
	int16Size   = 2
	float32Size = 4
)

func InitializeIfNeeded(c *opengl.Context) error {
	return theOpenGLState.initializeIfNeeded(c)
}

func (s *openGLState) initializeIfNeeded(c *opengl.Context) error {
	if s.initialized {
		return nil
	}

	var zeroProgram opengl.Program
	s.lastProgram = zeroProgram
	s.lastProjectionMatrix = nil
	s.lastModelviewMatrix = nil
	s.lastColorMatrix = nil

	shaderVertexModelviewNative, err := c.NewShader(c.VertexShader, shader(c, shaderVertexModelview))
	if err != nil {
		panic(fmt.Sprintf("graphics: shader compiling error:\n%s", err))
	}
	defer c.DeleteShader(shaderVertexModelviewNative)

	shaderFragmentTextureNative, err := c.NewShader(c.FragmentShader, shader(c, shaderFragmentTexture))
	if err != nil {
		panic(fmt.Sprintf("graphics: shader compiling error:\n%s", err))
	}
	defer c.DeleteShader(shaderFragmentTextureNative)

	s.programTexture, err = c.NewProgram([]opengl.Shader{
		shaderVertexModelviewNative,
		shaderFragmentTextureNative,
	})
	if err != nil {
		return err
	}

	// 16 [bytes] is an arbitrary number which seems enough to draw anything. Fix this if necessary.
	const stride = 16
	c.NewBuffer(c.ArrayBuffer, 4*stride*MaxQuads, c.DynamicDraw)

	indices := make([]uint16, 6*MaxQuads)
	for i := uint16(0); i < MaxQuads; i++ {
		indices[6*i+0] = 4*i + 0
		indices[6*i+1] = 4*i + 1
		indices[6*i+2] = 4*i + 2
		indices[6*i+3] = 4*i + 1
		indices[6*i+4] = 4*i + 2
		indices[6*i+5] = 4*i + 3
	}
	s.indexBufferQuads = c.NewBuffer(c.ElementArrayBuffer, indices, c.StaticDraw)

	indices = make([]uint16, indicesNum)
	for i := 0; i < len(indices); i++ {
		indices[i] = uint16(i)
	}
	s.indexBufferLines = c.NewBuffer(c.ElementArrayBuffer, indices, c.StaticDraw)

	s.initialized = true
	return nil
}

func areSameFloat32Array(a, b []float32) bool {
	if len(a) != len(b) {
		return false
	}
	for i := 0; i < len(a); i++ {
		if a[i] != b[i] {
			return false
		}
	}
	return true
}

type programContext struct {
	state            *openGLState
	program          opengl.Program
	context          *opengl.Context
	projectionMatrix []float32
	texture          opengl.Texture
	geoM             Matrix
	colorM           Matrix
}

func (p *programContext) begin() {
	c := p.context
	if p.state.lastProgram != p.program {
		c.UseProgram(p.program)
		p.state.lastProgram = p.state.programTexture
		p.state.lastProjectionMatrix = nil
		p.state.lastModelviewMatrix = nil
		p.state.lastColorMatrix = nil
	}
	c.BindElementArrayBuffer(p.state.indexBufferQuads)

	if !areSameFloat32Array(p.state.lastProjectionMatrix, p.projectionMatrix) {
		c.UniformFloats(p.program, "projection_matrix", p.projectionMatrix)
		if p.state.lastProjectionMatrix == nil {
			p.state.lastProjectionMatrix = make([]float32, 16)
		}
		copy(p.state.lastProjectionMatrix, p.projectionMatrix)
	}

	ma := float32(p.geoM.Element(0, 0))
	mb := float32(p.geoM.Element(0, 1))
	mc := float32(p.geoM.Element(1, 0))
	md := float32(p.geoM.Element(1, 1))
	tx := float32(p.geoM.Element(0, 2))
	ty := float32(p.geoM.Element(1, 2))
	modelviewMatrix := []float32{
		ma, mc, 0, 0,
		mb, md, 0, 0,
		0, 0, 1, 0,
		tx, ty, 0, 1,
	}
	if !areSameFloat32Array(p.state.lastModelviewMatrix, modelviewMatrix) {
		c.UniformFloats(p.program, "modelview_matrix", modelviewMatrix)
		if p.state.lastModelviewMatrix == nil {
			p.state.lastModelviewMatrix = make([]float32, 16)
		}
		copy(p.state.lastModelviewMatrix, modelviewMatrix)
	}

	c.UniformInt(p.program, "texture", 0)

	e := [4][5]float32{}
	for i := 0; i < 4; i++ {
		for j := 0; j < 5; j++ {
			e[i][j] = float32(p.colorM.Element(i, j))
		}
	}

	colorMatrix := []float32{
		e[0][0], e[1][0], e[2][0], e[3][0],
		e[0][1], e[1][1], e[2][1], e[3][1],
		e[0][2], e[1][2], e[2][2], e[3][2],
		e[0][3], e[1][3], e[2][3], e[3][3],
	}
	if !areSameFloat32Array(p.state.lastColorMatrix, colorMatrix) {
		c.UniformFloats(p.program, "color_matrix", colorMatrix)
		if p.state.lastColorMatrix == nil {
			p.state.lastColorMatrix = make([]float32, 16)
		}
		copy(p.state.lastColorMatrix, colorMatrix)
	}
	colorMatrixTranslation := []float32{
		e[0][4], e[1][4], e[2][4], e[3][4],
	}
	c.UniformFloats(p.program, "color_matrix_translation", colorMatrixTranslation)

	// We don't have to call gl.ActiveTexture here: GL_TEXTURE0 is the default active texture
	// See also: https://www.opengl.org/sdk/docs/man2/xhtml/glActiveTexture.xml
	c.BindTexture(p.texture)

	c.EnableVertexAttribArray(p.program, "vertex")
	c.EnableVertexAttribArray(p.program, "tex_coord")

	c.VertexAttribPointer(p.program, "vertex", false, int16Size*4, 2, int16Size*0)
	c.VertexAttribPointer(p.program, "tex_coord", true, int16Size*4, 2, int16Size*2)
}

func (p *programContext) end() {
	c := p.context
	c.DisableVertexAttribArray(p.program, "tex_coord")
	c.DisableVertexAttribArray(p.program, "vertex")
}