/**
 * @author Mat Groves
 *
 * Big thanks to the very clever Matt DesLauriers <mattdesl> https://github.com/mattdesl/
 * for creating the original pixi version!
 * Also a thanks to https://github.com/bchevalier for tweaking the tint and alpha so that they now share 4 bytes on the vertex buffer
 *
 * Heavily inspired by LibGDX's ParticleBuffer:
 * https://github.com/libgdx/libgdx/blob/master/gdx/src/com/badlogic/gdx/graphics/g2d/ParticleBuffer.java
 */

/**
 * The particle buffer manages the static and dynamic buffers for a particle container.
 *
 * @class
 * @private
 * @memberof PIXI
 */
function ParticleBuffer(gl, properties, dynamicPropertyFlags, size)
{
    /**
     * The current WebGL drawing context.
     *
     * @member {WebGLRenderingContext}
     */
    this.gl = gl;

    /**
     * Size of a single vertex.
     *
     * @member {number}
     */
    this.vertSize = 2;

    /**
     * Size of a single vertex in bytes.
     *
     * @member {number}
     */
    this.vertByteSize = this.vertSize * 4;

    /**
     * The number of particles the buffer can hold
     *
     * @member {number}
     */
    this.size = size;

    /**
     * A list of the properties that are dynamic.
     *
     * @member {object[]}
     */
    this.dynamicProperties = [];

    /**
     * A list of the properties that are static.
     *
     * @member {object[]}
     */
    this.staticProperties = [];

    for (var i = 0; i < properties.length; i++)
    {
        var property = properties[i];

        if(dynamicPropertyFlags[i])
        {
            this.dynamicProperties.push(property);
        }
        else
        {
            this.staticProperties.push(property);
        }
    }

    this.staticStride = 0;
    this.staticBuffer = null;
    this.staticData = null;

    this.dynamicStride = 0;
    this.dynamicBuffer = null;
    this.dynamicData = null;

    this.initBuffers();

}

ParticleBuffer.prototype.constructor = ParticleBuffer;
module.exports = ParticleBuffer;

/**
 * Sets up the renderer context and necessary buffers.
 *
 * @private
 */
ParticleBuffer.prototype.initBuffers = function ()
{
    var gl = this.gl;
    var i;
    var property;

    var dynamicOffset = 0;
    this.dynamicStride = 0;

    for (i = 0; i < this.dynamicProperties.length; i++)
    {
        property = this.dynamicProperties[i];

        property.offset = dynamicOffset;
        dynamicOffset += property.size;
        this.dynamicStride += property.size;
    }

    this.dynamicData = new Float32Array( this.size * this.dynamicStride * 4);
    this.dynamicBuffer = gl.createBuffer();

    gl.bindBuffer(gl.ARRAY_BUFFER, this.dynamicBuffer);
    gl.bufferData(gl.ARRAY_BUFFER, this.dynamicData, gl.DYNAMIC_DRAW);


    // static //
    var staticOffset = 0;
    this.staticStride = 0;

    for (i = 0; i < this.staticProperties.length; i++)
    {
        property = this.staticProperties[i];

        property.offset = staticOffset;
        staticOffset += property.size;
        this.staticStride += property.size;
    }

    this.staticData = new Float32Array( this.size * this.staticStride * 4);
    this.staticBuffer = gl.createBuffer();

    gl.bindBuffer(gl.ARRAY_BUFFER, this.staticBuffer);
    gl.bufferData(gl.ARRAY_BUFFER, this.staticData, gl.DYNAMIC_DRAW);
};

/**
 * Uploads the dynamic properties.
 *
 */
ParticleBuffer.prototype.uploadDynamic = function(children, startIndex, amount)
{
    var gl = this.gl;

    for (var i = 0; i < this.dynamicProperties.length; i++)
    {
        var property = this.dynamicProperties[i];
        property.uploadFunction(children, startIndex, amount, this.dynamicData, this.dynamicStride, property.offset);
    }

    gl.bindBuffer(gl.ARRAY_BUFFER, this.dynamicBuffer);
    gl.bufferSubData(gl.ARRAY_BUFFER, 0, this.dynamicData);
};

/**
 * Uploads the static properties.
 *
 */
ParticleBuffer.prototype.uploadStatic = function(children, startIndex, amount)
{
    var gl = this.gl;

    for (var i = 0; i < this.staticProperties.length; i++)
    {
        var property = this.staticProperties[i];
        property.uploadFunction(children, startIndex, amount, this.staticData, this.staticStride, property.offset);
    }

    gl.bindBuffer(gl.ARRAY_BUFFER, this.staticBuffer);
    gl.bufferSubData(gl.ARRAY_BUFFER, 0, this.staticData);
};

/**
 * Binds the buffers to the GPU
 *
 */
ParticleBuffer.prototype.bind = function ()
{
    var gl = this.gl;
    var i, property;

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

    for (i = 0; i < this.dynamicProperties.length; i++)
    {
        property = this.dynamicProperties[i];
        gl.vertexAttribPointer(property.attribute, property.size, gl.FLOAT, false, this.dynamicStride * 4, property.offset * 4);
    }

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

    for (i = 0; i < this.staticProperties.length; i++)
    {
        property = this.staticProperties[i];
        gl.vertexAttribPointer(property.attribute, property.size, gl.FLOAT, false, this.staticStride * 4, property.offset * 4);
    }
};

/**
 * Destroys the ParticleBuffer.
 *
 */
ParticleBuffer.prototype.destroy = function ()
{
    this.dynamicProperties = null;
    this.dynamicData = null;
    this.gl.deleteBuffer(this.dynamicBuffer);

    this.staticProperties = null;
    this.staticData = null;
    this.gl.deleteBuffer(this.staticBuffer);
};