/**
 * Thibault Durnez
 */

__private void rgb2hsv(const int src_r, const int src_g, const int src_b, float* dst_h, float* dst_s, float* dst_v);
__private void hsv2rgb(const float src_h, const float src_s, const float src_v, int* dst_r, int* dst_g, int* dst_b);

__kernel void hueshift(__global const int *inputImage, __global int *outputImage, int hueshift_param) {

    const size_t rowcol = (get_global_id(1) * get_global_size(0) + get_global_id(0));

    int color = inputImage[rowcol];
    int blue = (color & 0xFF0000) >> 16;
    int green = (color & 0x00FF00) >> 8;
    int red  = (color & 0x0000FF);

    float hue = 0;
    float saturation = 0;
    float value = 0;

    rgb2hsv(blue, green, red, &hue, &saturation, &value);
    hsv2rgb(fmod((hue + hueshift_param),360), saturation, value, &blue, &green, &red);


    int _blue =  (blue << 16) & 0xFF0000;
    int _green = (green << 8) & 0x00FF00;
    int _red =   (red << 0)   & 0x0000FF;

    int newColor = (color & 0xFF000000) | _blue | _green | _red;
    outputImage[rowcol] = newColor;
}


__private void rgb2hsv(const int src_r, const int src_g, const int src_b, float* dst_h, float* dst_s, float* dst_v) {
    float r = src_r / 255.0f;
    float g = src_g / 255.0f;
    float b = src_b / 255.0f;

    float h, s, v;

    float max = fmax(r, fmax(g, b));
    float min = fmin(r, fmin(g, b));

    v = max;

    if (max == 0.0f) {
        s = 0;
        h = 0;
    } else if (max - min == 0.0f) {
        s = 0;
        h = 0;
    } else {
        s = (max - min) / max;

        if (max == r) {
            h = 60 * ((g - b) / (max - min)) + 0;
        } else if (max == g) {
            h = 60 * ((b - r) / (max - min)) + 120;
        } else {
            h = 60 * ((r - g) / (max - min)) + 240;
        }
    }

    if (h < 0) h += 360.0f;

    *(dst_h) = (h / 2);
    *(dst_s) = (s * 255);
    *(dst_v) = (v * 255);
}


__private void hsv2rgb(const float src_h, const float src_s, const float src_v, int* dst_r, int* dst_g, int* dst_b) {

//    float h = (float) src_h;
    float h = src_h * 2.0f;
    float s = src_s / 255.0f;
    float v = src_v / 255.0f;

    float r, g, b;

    int hi = (int) (h / 60.0f) % 6;
    float f = (h / 60.0f) - hi;

    float p = v * (1.0f - s);
    float q = v * (1.0f - s * f);
    float t = v * (1.0f - s * (1.0f - f));

    switch (hi) {
        case 0:
            r = v, g = t, b = p;
            break;
        case 1:
            r = q, g = v, b = p;
            break;
        case 2:
            r = p, g = v, b = t;
            break;
        case 3:
            r = p, g = q, b = v;
            break;
        case 4:
            r = t, g = p, b = v;
            break;
        case 5:
            r = v, g = p, b = q;
            break;
        default:
            break;
    }

    *(dst_r) = (int)(r * 255);
    *(dst_g) = (int)(g * 255);
    *(dst_b) = (int)(b * 255);
}