const GAUSSIAN_VALUES = {
    5:[0.153388, 0.221461, 0.250301],
    7:[0.071303, 0.131514, 0.189879, 0.214607],
    9:[0.028532, 0.067234, 0.124009, 0.179044, 0.20236],
    11:[0.0093, 0.028002, 0.065984, 0.121703, 0.175713, 0.198596],
    13:[0.002406, 0.009255, 0.027867, 0.065666, 0.121117, 0.174868, 0.197641],
    15:[0.000489, 0.002403, 0.009246, 0.02784, 0.065602, 0.120999, 0.174697, 0.197448]
};

const fragTemplate = [
    'varying vec2 vBlurTexCoords[%size%];',
    'uniform sampler2D uSampler;',

    'void main(void)',
    '{',
    '    gl_FragColor = vec4(0.0);',
    '    %blur%',
    '}'

].join('\n');

const generateFragBlurSource = function(kernelSize)
{
    let kernel = GAUSSIAN_VALUES[kernelSize];
    let halfLength = kernel.length;

    let fragSource = fragTemplate;

    let blurLoop = '';
    let template = 'gl_FragColor += texture2D(uSampler, vBlurTexCoords[%index%]) * %value%;';
        let value;

    for (let i = 0; i < kernelSize; i++)
    {
        let blur = template.replace('%index%', i);

        value = i;

        if(i >= halfLength)
        {
            value = kernelSize - i - 1;
        }


        blur = blur.replace('%value%', kernel[value]);

        blurLoop += blur;
        blurLoop += '\n';
    }

    fragSource = fragSource.replace('%blur%', blurLoop);
    fragSource = fragSource.replace('%size%', kernelSize);


    return fragSource;
};

export default generateFragBlurSource;