/**
 * Constructs a renderer object.
 * @param {WebGLRenderingContext} gl The GL context.
 * @constructor
 */
var Renderer = function (gl) {
   /**
    * The GL context.
    * @type {WebGLRenderingContext}
    * @private
    */
   this.gl_ = gl;

   /**
    * The WebGLProgram.
    * @type {WebGLProgram}
    * @private
    */
   this.program_ = gl.createProgram();

   /**
    * @type {WebGLShader}
    * @private
    */
   this.vertexShader_ = this.compileShader_(
      Renderer.vertexShaderSource_, gl.VERTEX_SHADER);

   /**
    * @type {WebGLShader}
    * @private
    */
   this.fragmentShader_ = this.compileShader_(
      Renderer.fragmentShaderSource_, gl.FRAGMENT_SHADER);

   /**
    * Cached uniform locations.
    * @type {Object.<string, WebGLUniformLocation>}
    * @private
    */
   this.uniformLocations_ = {};

   /**
    * Cached attribute locations.
    * @type {Object.<string, WebGLActiveInfo>}
    * @private
    */
   this.attribLocations_ = {};

   /**
    * A vertex buffer containing a single quad with xy coordinates from [-1,-1]
    * to [1,1] and uv coordinates from [0,0] to [1,1].
    * @private
    */
   this.quadVertexBuffer_ = gl.createBuffer();
   gl.bindBuffer(gl.ARRAY_BUFFER, this.quadVertexBuffer_);
   var vertices = new Float32Array(
      [-1.0, -1.0, 0.0, 1.0,
      +1.0, -1.0, 1.0, 1.0,
      -1.0, +1.0, 0.0, 0.0,
         1.0, +1.0, 1.0, 0.0]);
   gl.bufferData(gl.ARRAY_BUFFER, vertices, gl.STATIC_DRAW);


   // init shaders

   gl.attachShader(this.program_, this.vertexShader_);
   gl.attachShader(this.program_, this.fragmentShader_);
   gl.bindAttribLocation(this.program_, 0, 'vert');
   gl.linkProgram(this.program_);
   gl.useProgram(this.program_);
   gl.enableVertexAttribArray(0);

   gl.enable(gl.DEPTH_TEST);
   gl.disable(gl.CULL_FACE);

   var count = gl.getProgramParameter(this.program_, gl.ACTIVE_UNIFORMS);
   for (var i = 0; i < /** @type {number} */(count); i++) {
      var info = gl.getActiveUniform(this.program_, i);
      var result = gl.getUniformLocation(this.program_, info.name);
      this.uniformLocations_[info.name] = result;
   }

   count = gl.getProgramParameter(this.program_, gl.ACTIVE_ATTRIBUTES);
   for (var i = 0; i < /** @type {number} */(count); i++) {
      var info = gl.getActiveAttrib(this.program_, i);
      var result = gl.getAttribLocation(this.program_, info.name);
      this.attribLocations_[info.name] = result;
   }
};


Renderer.prototype.finishInit = function () {
   this.draw();
};


Renderer.prototype.createDxtTexture = function (dxtData, width, height, format) {
   var gl = this.gl_;
   var tex = gl.createTexture();
   gl.bindTexture(gl.TEXTURE_2D, tex);
   gl.compressedTexImage2D(
      gl.TEXTURE_2D,
      0,
      format,
      width,
      height,
      0,
      dxtData);
   gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.NEAREST);
   gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.NEAREST);
   gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE);
   gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE);
   gl.bindTexture(gl.TEXTURE_2D, null);
   return tex;
};

Renderer.prototype.createCompressedTexture = function (data, width, height, format) {
   var gl = this.gl_;
   var tex = gl.createTexture();
   gl.bindTexture(gl.TEXTURE_2D, tex);
   gl.compressedTexImage2D(
      gl.TEXTURE_2D,
      0,
      format,
      width,
      height,
      0,
      data);
   gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.NEAREST);
   gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.NEAREST);
   gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE);
   gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE);
   gl.bindTexture(gl.TEXTURE_2D, null);
   return tex;
};

Renderer.prototype.createHalfRGBATexture = function (data, width, height, format) {
   var gl = this.gl_;
   var tex = gl.createTexture();
   gl.bindTexture(gl.TEXTURE_2D, tex);
   gl.texImage2D(
      gl.TEXTURE_2D,
      0,
      gl.RGBA,
      width,
      height,
      0,
      gl.RGBA,
      format,
      data);
   gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.NEAREST);
   gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.NEAREST);
   gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE);
   gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE);
   gl.bindTexture(gl.TEXTURE_2D, null);
   return tex;
};

Renderer.prototype.createRgb565Texture = function (rgb565Data, width, height) {
   var gl = this.gl_;
   var tex = gl.createTexture();
   gl.bindTexture(gl.TEXTURE_2D, tex);
   gl.texImage2D(
      gl.TEXTURE_2D,
      0,
      gl.RGB,
      width,
      height,
      0,
      gl.RGB,
      gl.UNSIGNED_SHORT_5_6_5,
      rgb565Data);
   gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.NEAREST);
   gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.NEAREST);
   gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE);
   gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE);
   gl.bindTexture(gl.TEXTURE_2D, null);
   return tex;
};

Renderer.prototype.createRgbaTexture = function (rgbaData, width, height) {
   var gl = this.gl_;
   var tex = gl.createTexture();
   gl.bindTexture(gl.TEXTURE_2D, tex);
   gl.texImage2D(
      gl.TEXTURE_2D,
      0,
      gl.RGBA,
      width,
      height,
      0,
      gl.RGBA,
      gl.UNSIGNED_BYTE,
      rgbaData);
   gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.NEAREST);
   gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.NEAREST);
   gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE);
   gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE);
   gl.bindTexture(gl.TEXTURE_2D, null);
   return tex;
};


Renderer.prototype.drawTexture = function (texture, width, height, mode, scale, linearToSRGBFlag) {
   var gl = this.gl_;
   // draw scene
   gl.clearColor(0, 0, 0, 1);
   gl.clearDepth(1.0);
   gl.viewport(0, 0, width, height);
   gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT | gl.STENCIL_BUFFER_BIT);

   gl.activeTexture(gl.TEXTURE0);
   gl.bindTexture(gl.TEXTURE_2D, texture);
   gl.uniform1i(this.uniformLocations_.texSampler, 0);

   var x = 0.0;
   var y = 0.0;
   if (mode == 1)
      x = 1.0;
   else if (mode == 2)
      y = 1.0;

   gl.uniform4f(this.uniformLocations_.control, x, y, scale, linearToSRGBFlag ? 1.0 : 0.0);

   gl.enableVertexAttribArray(this.attribLocations_.vert);
   gl.bindBuffer(gl.ARRAY_BUFFER, this.quadVertexBuffer_);
   gl.vertexAttribPointer(this.attribLocations_.vert, 4, gl.FLOAT,
      false, 0, 0);
   gl.drawArrays(gl.TRIANGLE_STRIP, 0, 4);
};


/**
 * Compiles a GLSL shader and returns a WebGLShader.
 * @param {string} shaderSource The shader source code string.
 * @param {number} type Either VERTEX_SHADER or FRAGMENT_SHADER.
 * @return {WebGLShader} The new WebGLShader.
 * @private
 */
Renderer.prototype.compileShader_ = function (shaderSource, type) {
   var gl = this.gl_;
   var shader = gl.createShader(type);
   gl.shaderSource(shader, shaderSource);
   gl.compileShader(shader);
   return shader;
};


/**
 * @type {string}
 * @private
 */
Renderer.vertexShaderSource_ = [
   'attribute vec4 vert;',
   'varying vec2 v_texCoord;',
   'void main() {',
   '  gl_Position = vec4(vert.xy, 0.0, 1.0);',
   '  v_texCoord = vert.zw;',
   '}'
].join('\n');


/**
 * @type {string}
 * @private '  gl_FragColor = texture2D(texSampler, v_texCoord);',
 */
Renderer.fragmentShaderSource_ = [
   'precision highp float;',
   'uniform sampler2D texSampler;',
   'uniform vec4 control;',
   'varying vec2 v_texCoord;',

   // Function to convert linear RGB to sRGB
   'vec3 linearToSrgb(vec3 linearRGB) {',
   '  vec3 srgbLow = linearRGB * 12.92;',
   '  vec3 srgbHigh = 1.055 * pow(linearRGB, vec3(1.0/2.4)) - 0.055;',
   '  return clamp(mix(srgbLow, srgbHigh, step(0.0031308, linearRGB)), 0.0, 1.0);',
   '}',

   'void main() {',
   '  vec4 c;',
   '  c = texture2D(texSampler, v_texCoord);',
   '  c.rgb *= control.z;',
   '  if (control.x > 0.0)',
   '  {',
   '   	c.w = 1.0;',
   '  }',
   '	 else if (control.y > 0.0)',
   '	 {',
   '   	c.rgb = c.aaa; c.w = 1.0;',
   '  }',
   '  if (control.w > 0.0)',
   '     c.rgb = linearToSrgb(c.rgb);',
   '  gl_FragColor = c;',
   '}'
].join('\n');