var EMPTY_ARRAY_BUFFER = new ArrayBuffer(0);

/**
 * Helper class to create a webGL buffer
 *
 * @class
 * @memberof PIXI.glCore
 * @param gl {WebGLRenderingContext} The current WebGL rendering context
 * @param type {gl.ARRAY_BUFFER | gl.ELEMENT_ARRAY_BUFFER} @mat
 * @param data {ArrayBuffer| SharedArrayBuffer|ArrayBufferView} an array of data
 * @param drawType {gl.STATIC_DRAW|gl.DYNAMIC_DRAW|gl.STREAM_DRAW}
 */
var Buffer = function(gl, type, data, drawType)
{

	/**
     * The current WebGL rendering context
     *
     * @member {WebGLRenderingContext}
     */
	this.gl = gl;

	/**
     * The WebGL buffer, created upon instantiation
     *
     * @member {WebGLBuffer}
     */
	this.buffer = gl.createBuffer();

	/**
     * The type of the buffer
     *
     * @member {gl.ARRAY_BUFFER|gl.ELEMENT_ARRAY_BUFFER}
     */
	this.type = type || gl.ARRAY_BUFFER;

	/**
     * The draw type of the buffer
     *
     * @member {gl.STATIC_DRAW|gl.DYNAMIC_DRAW|gl.STREAM_DRAW}
     */
	this.drawType = drawType || gl.STATIC_DRAW;

	/**
     * The data in the buffer, as a typed array
     *
     * @member {ArrayBuffer| SharedArrayBuffer|ArrayBufferView}
     */
	this.data = EMPTY_ARRAY_BUFFER;

	if(data)
	{
		this.upload(data);
	}

	this._updateID = 0;
};

/**
 * Uploads the buffer to the GPU
 * @param data {ArrayBuffer| SharedArrayBuffer|ArrayBufferView} an array of data to upload
 * @param offset {Number} if only a subset of the data should be uploaded, this is the amount of data to subtract
 * @param dontBind {Boolean} whether to bind the buffer before uploading it
 */
Buffer.prototype.upload = function(data, offset, dontBind)
{
	// todo - needed?
	if(!dontBind) this.bind();

	var gl = this.gl;

	data = data || this.data;
	offset = offset || 0;

	if(this.data.byteLength >= data.byteLength)
	{
		gl.bufferSubData(this.type, offset, data);
	}
	else
	{
		gl.bufferData(this.type, data, this.drawType);
	}

	this.data = data;
};
/**
 * Binds the buffer
 *
 */
Buffer.prototype.bind = function()
{
	var gl = this.gl;
	gl.bindBuffer(this.type, this.buffer);
};

Buffer.createVertexBuffer = function(gl, data, drawType)
{
	return new Buffer(gl, gl.ARRAY_BUFFER, data, drawType);
};

Buffer.createIndexBuffer = function(gl, data, drawType)
{
	return new Buffer(gl, gl.ELEMENT_ARRAY_BUFFER, data, drawType);
};

Buffer.create = function(gl, type, data, drawType)
{
	return new Buffer(gl, type, data, drawType);
};

/**
 * Destroys the buffer
 *
 */
Buffer.prototype.destroy = function(){
	this.gl.deleteBuffer(this.buffer);
};

module.exports = Buffer;