/**
 * @author Mat Groves http://matgroves.com/ @Doormat23
 */

PIXI._batchs = [];

/**
 * @private
 */
PIXI._getBatch = function(gl)
{
	if(PIXI._batchs.length == 0)
	{
		return new PIXI.WebGLBatch(gl);
	}
	else
	{
		return PIXI._batchs.pop();
	}
}

/**
 * @private
 */
PIXI._returnBatch = function(batch)
{
	batch.clean();	
	PIXI._batchs.push(batch);
}

/**
 * @private
 */
PIXI._restoreBatchs = function(gl)
{
	for (var i=0; i < PIXI._batchs.length; i++) 
	{
	  PIXI._batchs[i].restoreLostContext(gl);
	};
}

/**
 * A WebGLBatch Enables a group of sprites to be drawn using the same settings.
 * if a group of sprites all have the same baseTexture and blendMode then they can be grouped into a batch.
 * All the sprites in a batch can then be drawn in one go by the GPU which is hugely efficient. ALL sprites
 * in the webGL renderer are added to a batch even if the batch only contains one sprite. Batching is handled
 * automatically by the webGL renderer. A good tip is: the smaller the number of batchs there are, the faster
 * the webGL renderer will run.
 *
 * @class WebGLBatch
 * @constructor
 * @param gl {WebGLContext} an instance of the webGL context
 */
PIXI.WebGLBatch = function(gl)
{
	this.gl = gl;
	
	this.size = 0;

	this.vertexBuffer =  gl.createBuffer();
	this.indexBuffer =  gl.createBuffer();
	this.uvBuffer =  gl.createBuffer();
	this.colorBuffer =  gl.createBuffer();
	this.blendMode = PIXI.blendModes.NORMAL;
	this.dynamicSize = 1;
}

// constructor
PIXI.WebGLBatch.prototype.constructor = PIXI.WebGLBatch;

/**
 * Cleans the batch so that is can be returned to an object pool and reused
 *
 * @method clean
 */
PIXI.WebGLBatch.prototype.clean = function()
{
	this.verticies = [];
	this.uvs = [];
	this.indices = [];
	this.colors = [];
	this.dynamicSize = 1;
	this.texture = null;
	this.last = null;
	this.size = 0;
	this.head;
	this.tail;
}

/**
 * Recreates the buffers in the event of a context loss
 *
 * @method restoreLostContext
 * @param gl {WebGLContext}
 */
PIXI.WebGLBatch.prototype.restoreLostContext = function(gl)
{
	this.gl = gl;
	this.vertexBuffer =  gl.createBuffer();
	this.indexBuffer =  gl.createBuffer();
	this.uvBuffer =  gl.createBuffer();
	this.colorBuffer =  gl.createBuffer();
}

/**
 * inits the batch's texture and blend mode based if the supplied sprite
 *
 * @method init
 * @param sprite {Sprite} the first sprite to be added to the batch. Only sprites with
 *		the same base texture and blend mode will be allowed to be added to this batch
 */	
PIXI.WebGLBatch.prototype.init = function(sprite)
{
	sprite.batch = this;
	this.dirty = true;
	this.blendMode = sprite.blendMode;
	this.texture = sprite.texture.baseTexture;
	this.head = sprite;
	this.tail = sprite;
	this.size = 1;

	this.growBatch();
}

/**
 * inserts a sprite before the specified sprite
 *
 * @method insertBefore
 * @param sprite {Sprite} the sprite to be added
 * @param nextSprite {nextSprite} the first sprite will be inserted before this sprite
 */	
PIXI.WebGLBatch.prototype.insertBefore = function(sprite, nextSprite)
{
	this.size++;

	sprite.batch = this;
	this.dirty = true;
	var tempPrev = nextSprite.__prev;
	nextSprite.__prev = sprite;
	sprite.__next = nextSprite;

	if(tempPrev)
	{
		sprite.__prev = tempPrev;
		tempPrev.__next = sprite;
	}
	else
	{
		this.head = sprite;
	}
}

/**
 * inserts a sprite after the specified sprite
 *
 * @method insertAfter
 * @param sprite {Sprite} the sprite to be added
 * @param  previousSprite {Sprite} the first sprite will be inserted after this sprite
 */	
PIXI.WebGLBatch.prototype.insertAfter = function(sprite, previousSprite)
{
	this.size++;

	sprite.batch = this;
	this.dirty = true;

	var tempNext = previousSprite.__next;
	previousSprite.__next = sprite;
	sprite.__prev = previousSprite;

	if(tempNext)
	{
		sprite.__next = tempNext;
		tempNext.__prev = sprite;
	}
	else
	{
		this.tail = sprite
	}
}

/**
 * removes a sprite from the batch
 *
 * @method remove
 * @param sprite {Sprite} the sprite to be removed
 */	
PIXI.WebGLBatch.prototype.remove = function(sprite)
{
	this.size--;

	if(this.size == 0)
	{
		sprite.batch = null;
		sprite.__prev = null;
		sprite.__next = null;
		return;
	}

	if(sprite.__prev)
	{
		sprite.__prev.__next = sprite.__next;
	}
	else
	{
		this.head = sprite.__next;
		this.head.__prev = null;
	}

	if(sprite.__next)
	{
		sprite.__next.__prev = sprite.__prev;
	}
	else
	{
		this.tail = sprite.__prev;
		this.tail.__next = null
	}

	sprite.batch = null;
	sprite.__next = null;
	sprite.__prev = null;
	this.dirty = true;
}

/**
 * Splits the batch into two with the specified sprite being the start of the new batch.
 *
 * @method split
 * @param sprite {Sprite} the sprite that indicates where the batch should be split
 * @return {WebGLBatch} the new batch
 */
PIXI.WebGLBatch.prototype.split = function(sprite)
{
	this.dirty = true;

	var batch = new PIXI.WebGLBatch(this.gl);
	batch.init(sprite);
	batch.texture = this.texture;
	batch.tail = this.tail;

	this.tail = sprite.__prev;
	this.tail.__next = null;

	sprite.__prev = null;
	// return a splite batch!

	// TODO this size is wrong!
	// need to recalculate :/ problem with a linked list!
	// unless it gets calculated in the "clean"?

	// need to loop through items as there is no way to know the length on a linked list :/
	var tempSize = 0;
	while(sprite)
	{
		tempSize++;
		sprite.batch = batch;
		sprite = sprite.__next;
	}

	batch.size = tempSize;
	this.size -= tempSize;

	return batch;
}

/**
 * Merges two batchs together
 *
 * @method merge
 * @param batch {WebGLBatch} the batch that will be merged 
 */
PIXI.WebGLBatch.prototype.merge = function(batch)
{
	this.dirty = true;

	this.tail.__next = batch.head;
	batch.head.__prev = this.tail;

	this.size += batch.size;

	this.tail = batch.tail;

	var sprite = batch.head;
	while(sprite)
	{
		sprite.batch = this;
		sprite = sprite.__next;
	}
}

/**
 * Grows the size of the batch. As the elements in the batch cannot have a dynamic size this
 * function is used to increase the size of the batch. It also creates a little extra room so
 * that the batch does not need to be resized every time a sprite is added
 *
 * @method growBatch
 */
PIXI.WebGLBatch.prototype.growBatch = function()
{
	var gl = this.gl;
	if( this.size == 1)
	{
		this.dynamicSize = 1;
	}
	else
	{
		this.dynamicSize = this.size * 1.5
	}
	// grow verts
	this.verticies = new Float32Array(this.dynamicSize * 8);

	gl.bindBuffer(gl.ARRAY_BUFFER, this.vertexBuffer);
	gl.bufferData(gl.ARRAY_BUFFER,this.verticies , gl.DYNAMIC_DRAW);

	this.uvs  = new Float32Array( this.dynamicSize * 8 );
	gl.bindBuffer(gl.ARRAY_BUFFER, this.uvBuffer);
	gl.bufferData(gl.ARRAY_BUFFER, this.uvs , gl.DYNAMIC_DRAW);

	this.dirtyUVS = true;

	this.colors  = new Float32Array( this.dynamicSize * 4 );
	gl.bindBuffer(gl.ARRAY_BUFFER, this.colorBuffer);
	gl.bufferData(gl.ARRAY_BUFFER, this.colors , gl.DYNAMIC_DRAW);

	this.dirtyColors = true;

	this.indices = new Uint16Array(this.dynamicSize * 6); 
	var length = this.indices.length/6;

	for (var i=0; i < length; i++) 
	{
	    var index2 = i * 6;
	    var index3 = i * 4;
		this.indices[index2 + 0] = index3 + 0;
		this.indices[index2 + 1] = index3 + 1;
		this.indices[index2 + 2] = index3 + 2;
		this.indices[index2 + 3] = index3 + 0;
		this.indices[index2 + 4] = index3 + 2;
		this.indices[index2 + 5] = index3 + 3;
	};

	gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, this.indexBuffer);
    gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, this.indices, gl.STATIC_DRAW);
}

/**
 * Refresh's all the data in the batch and sync's it with the webGL buffers
 *
 * @method refresh
 */
PIXI.WebGLBatch.prototype.refresh = function()
{
	var gl = this.gl;

	if (this.dynamicSize < this.size)
	{
		this.growBatch();
	}

	var indexRun = 0;
	var worldTransform, width, height, aX, aY, w0, w1, h0, h1, index;
	var a, b, c, d, tx, ty;

	var displayObject = this.head;

	while(displayObject)
	{
		index = indexRun * 8;

		var texture = displayObject.texture;

		var frame = texture.frame;
		var tw = texture.baseTexture.width;
		var th = texture.baseTexture.height;

		this.uvs[index + 0] = frame.x / tw;
		this.uvs[index +1] = frame.y / th;

		this.uvs[index +2] = (frame.x + frame.width) / tw;
		this.uvs[index +3] = frame.y / th;

		this.uvs[index +4] = (frame.x + frame.width) / tw;
		this.uvs[index +5] = (frame.y + frame.height) / th; 

		this.uvs[index +6] = frame.x / tw;
		this.uvs[index +7] = (frame.y + frame.height) / th;

		displayObject.updateFrame = false;

		colorIndex = indexRun * 4;
		this.colors[colorIndex] = this.colors[colorIndex + 1] = this.colors[colorIndex + 2] = this.colors[colorIndex + 3] = displayObject.worldAlpha;

		displayObject = displayObject.__next;

		indexRun ++;
	}

	this.dirtyUVS = true;
	this.dirtyColors = true;
}

/**
 * Updates all the relevant geometry and uploads the data to the GPU
 *
 * @method update
 */
PIXI.WebGLBatch.prototype.update = function()
{
	var gl = this.gl;
	var worldTransform, width, height, aX, aY, w0, w1, h0, h1, index, index2, index3

	var a, b, c, d, tx, ty;

	var indexRun = 0;

	var displayObject = this.head;

	while(displayObject)
	{
		if(displayObject.vcount === PIXI.visibleCount)
		{
			width = displayObject.texture.frame.width;
			height = displayObject.texture.frame.height;

			// TODO trim??
			aX = displayObject.anchor.x;// - displayObject.texture.trim.x
			aY = displayObject.anchor.y; //- displayObject.texture.trim.y
			w0 = width * (1-aX);
			w1 = width * -aX;

			h0 = height * (1-aY);
			h1 = height * -aY;

			index = indexRun * 8;

			worldTransform = displayObject.worldTransform;

			a = worldTransform[0];
			b = worldTransform[3];
			c = worldTransform[1];
			d = worldTransform[4];
			tx = worldTransform[2];
			ty = worldTransform[5];

			this.verticies[index + 0 ] = a * w1 + c * h1 + tx; 
			this.verticies[index + 1 ] = d * h1 + b * w1 + ty;

			this.verticies[index + 2 ] = a * w0 + c * h1 + tx; 
			this.verticies[index + 3 ] = d * h1 + b * w0 + ty; 

			this.verticies[index + 4 ] = a * w0 + c * h0 + tx; 
			this.verticies[index + 5 ] = d * h0 + b * w0 + ty; 

			this.verticies[index + 6] =  a * w1 + c * h0 + tx; 
			this.verticies[index + 7] =  d * h0 + b * w1 + ty; 

			if(displayObject.updateFrame || displayObject.texture.updateFrame)
			{
				this.dirtyUVS = true;

				var texture = displayObject.texture;

				var frame = texture.frame;
				var tw = texture.baseTexture.width;
				var th = texture.baseTexture.height;

				this.uvs[index + 0] = frame.x / tw;
				this.uvs[index +1] = frame.y / th;

				this.uvs[index +2] = (frame.x + frame.width) / tw;
				this.uvs[index +3] = frame.y / th;

				this.uvs[index +4] = (frame.x + frame.width) / tw;
				this.uvs[index +5] = (frame.y + frame.height) / th; 

				this.uvs[index +6] = frame.x / tw;
				this.uvs[index +7] = (frame.y + frame.height) / th;

				displayObject.updateFrame = false;
			}

			// TODO this probably could do with some optimisation....
			if(displayObject.cacheAlpha != displayObject.worldAlpha)
			{
				displayObject.cacheAlpha = displayObject.worldAlpha;

				var colorIndex = indexRun * 4;
				this.colors[colorIndex] = this.colors[colorIndex + 1] = this.colors[colorIndex + 2] = this.colors[colorIndex + 3] = displayObject.worldAlpha;
				this.dirtyColors = true;
			}
		}
		else
		{
			index = indexRun * 8;

			this.verticies[index + 0 ] = 0;
			this.verticies[index + 1 ] = 0;

			this.verticies[index + 2 ] = 0;
			this.verticies[index + 3 ] = 0;

			this.verticies[index + 4 ] = 0;
			this.verticies[index + 5 ] = 0;

			this.verticies[index + 6] = 0;
			this.verticies[index + 7] = 0;
		}

		indexRun++;
		displayObject = displayObject.__next;
   }
}

/**
 * Draws the batch to the frame buffer
 *
 * @method render
 */
PIXI.WebGLBatch.prototype.render = function(start, end)
{
	start = start || 0;

	if(end == undefined)end = this.size;
	
	if(this.dirty)
	{
		this.refresh();
		this.dirty = false;
	}

	if (this.size == 0)return;

	this.update();
	var gl = this.gl;

	//TODO optimize this!

	var shaderProgram = PIXI.currentShader;
	
	//gl.useProgram(shaderProgram);

	// update the verts..
	gl.bindBuffer(gl.ARRAY_BUFFER, this.vertexBuffer);
	// ok..
	gl.bufferSubData(gl.ARRAY_BUFFER, 0, this.verticies)
    gl.vertexAttribPointer(shaderProgram.vertexPositionAttribute, 2, gl.FLOAT, false, 0, 0);
	// update the uvs
	var isDefault = (shaderProgram == PIXI.shaderProgram)

   	gl.bindBuffer(gl.ARRAY_BUFFER, this.uvBuffer);

    if(this.dirtyUVS)
    {
    	this.dirtyUVS = false;
    	gl.bufferSubData(gl.ARRAY_BUFFER,  0, this.uvs);
    }

    gl.vertexAttribPointer(shaderProgram.textureCoordAttribute, 2, gl.FLOAT, false, 0, 0);

    gl.activeTexture(gl.TEXTURE0);
    gl.bindTexture(gl.TEXTURE_2D, this.texture._glTexture);

	// update color!
	gl.bindBuffer(gl.ARRAY_BUFFER, this.colorBuffer);

	if(this.dirtyColors)
    {
    	this.dirtyColors = false;
    	gl.bufferSubData(gl.ARRAY_BUFFER, 0, this.colors);
	}

    gl.vertexAttribPointer(shaderProgram.colorAttribute, 1, gl.FLOAT, false, 0, 0);
	// dont need to upload!
    gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, this.indexBuffer);

	var len = end - start;

    // DRAW THAT this!
    gl.drawElements(gl.TRIANGLES, len * 6, gl.UNSIGNED_SHORT, start * 2 * 6 );
}