// adapted from: https://gist.github.com/nowl/828013#gistcomment-2807232
#include "perlin.h"
#include "math.h"

static const uint8_t PERLIN_PERM_TABLE[] = {
    208,34,231,213,32,248,233,56,161,78,24,140,71,48,140,254,245,255,247,247,40,
    185,248,251,245,28,124,204,204,76,36,1,107,28,234,163,202,224,245,128,167,204,
    9,92,217,54,239,174,173,102,193,189,190,121,100,108,167,44,43,77,180,204,8,81,
    70,223,11,38,24,254,210,210,177,32,81,195,243,125,8,169,112,32,97,53,195,13,
    203,9,47,104,125,117,114,124,165,203,181,235,193,206,70,180,174,0,167,181,41,
    164,30,116,127,198,245,146,87,224,149,206,57,4,192,210,65,210,129,240,178,105,
    228,108,245,148,140,40,35,195,38,58,65,207,215,253,65,85,208,76,62,3,237,55,89,
    232,50,217,64,244,157,199,121,252,90,17,212,203,149,152,140,187,234,177,73,174,
    193,100,192,143,97,53,145,135,19,103,13,90,135,151,199,91,239,247,33,39,145,
    101,120,99,3,186,86,99,41,237,203,111,79,220,135,158,42,30,154,120,67,87,167,
    135,176,183,191,253,115,184,21,233,58,129,233,142,39,128,211,118,137,139,255,
    114,20,218,113,154,27,127,246,250,1,8,198,250,209,92,222,173,21,88,102,219
};

static int32_t perlin_noise2_sample(int32_t seed, int32_t x, int32_t y) {
    int32_t yindex = (y + seed) % 256;
    if (yindex < 0)
        yindex += 256;
    int32_t xindex = (PERLIN_PERM_TABLE[yindex] + x) % 256;
    if (xindex < 0)
        xindex += 256;
    return PERLIN_PERM_TABLE[xindex];
}

static double perlin_lerp(double x, double y, double t) {
    return x + t*(y - x);
}

static double perlin_smooth_lerp(double x, double y, double t) {
    return perlin_lerp(x, y, t * t * (3-2*t));
}

double perlin_noise2d(int32_t seed, double x, double y) {
    int32_t x_int = floor(x);
    int32_t y_int = floor(y);
    double x_frac = x - x_int;
    double y_frac = y - y_int;
    int32_t s = perlin_noise2_sample(seed, x_int, y_int);
    int32_t t = perlin_noise2_sample(seed, x_int+1, y_int);
    int32_t u = perlin_noise2_sample(seed, x_int, y_int+1);
    int32_t v = perlin_noise2_sample(seed, x_int+1, y_int+1);
    double low = perlin_smooth_lerp(s, t, x_frac);
    double high = perlin_smooth_lerp(u, v, x_frac);
    double result = perlin_smooth_lerp(low, high, y_frac);
    return result;
}

double perlin_fbm(int32_t seed, double x, double y, double freq, uint32_t octaves) {
    double xa = x*freq;
    double ya = y*freq;
    double amp = 1.0;
    double res = 0.0;
    double div = 0.0;

    for (uint32_t i=0; i<octaves; i++) {
        div += 256.0 * amp;
        res += perlin_noise2d(seed, xa, ya) * amp;
        amp *= 0.5;
        xa *= 2.0;
        ya *= 2.0;
    }

    return res/div;
}