#include "util/random/perlin.h"

#include <math.h>

// This should go in the const section of the binary.
static const int p[512] = {
  151,160,137,91,90,15,
  131,13,201,95,96,53,194,233,7,225,140,36,103,30,69,142,8,99,37,240,21,10,23,
  190, 6,148,247,120,234,75,0,26,197,62,94,252,219,203,117,35,11,32,57,177,33,
  88,237,149,56,87,174,20,125,136,171,168, 68,175,74,165,71,134,139,48,27,166,
  77,146,158,231,83,111,229,122,60,211,133,230,220,105,92,41,55,46,245,40,244,
  102,143,54, 65,25,63,161, 1,216,80,73,209,76,132,187,208, 89,18,169,200,196,
  135,130,116,188,159,86,164,100,109,198,173,186, 3,64,52,217,226,250,124,123,
  5,202,38,147,118,126,255,82,85,212,207,206,59,227,47,16,58,17,182,189,28,42,
  223,183,170,213,119,248,152, 2,44,154,163, 70,221,153,101,155,167, 43,172,9,
  129,22,39,253, 19,98,108,110,79,113,224,232,178,185, 112,104,218,246,97,228,
  251,34,242,193,238,210,144,12,191,179,162,241, 81,51,145,235,249,14,239,107,
  49,192,214, 31,181,199,106,157,184, 84,204,176,115,121,50,45,127, 4,150,254,
  138,236,205,93,222,114,67,29,24,72,243,141,128,195,78,66,215,61,156,180,
  151,160,137,91,90,15,
  131,13,201,95,96,53,194,233,7,225,140,36,103,30,69,142,8,99,37,240,21,10,23,
  190, 6,148,247,120,234,75,0,26,197,62,94,252,219,203,117,35,11,32,57,177,33,
  88,237,149,56,87,174,20,125,136,171,168, 68,175,74,165,71,134,139,48,27,166,
  77,146,158,231,83,111,229,122,60,211,133,230,220,105,92,41,55,46,245,40,244,
  102,143,54, 65,25,63,161, 1,216,80,73,209,76,132,187,208, 89,18,169,200,196,
  135,130,116,188,159,86,164,100,109,198,173,186, 3,64,52,217,226,250,124,123,
  5,202,38,147,118,126,255,82,85,212,207,206,59,227,47,16,58,17,182,189,28,42,
  223,183,170,213,119,248,152, 2,44,154,163, 70,221,153,101,155,167, 43,172,9,
  129,22,39,253, 19,98,108,110,79,113,224,232,178,185, 112,104,218,246,97,228,
  251,34,242,193,238,210,144,12,191,179,162,241, 81,51,145,235,249,14,239,107,
  49,192,214, 31,181,199,106,157,184, 84,204,176,115,121,50,45,127, 4,150,254,
  138,236,205,93,222,114,67,29,24,72,243,141,128,195,78,66,215,61,156,180,
};

inline float fade(float t) {
  return t * t * t * (t * (t * 6 - 15) + 10);
}

inline float lerp(float t, float a, float b) {
  return a + t * (b - a);
}

inline float grad(int hash, float x, float y, float z) {
  int h = hash & 15;                             // CONVERT LO 4 BITS OF HASH CODE
  float u = h < 8 ? x : y;                       // INTO 12 GRADIENT DIRECTIONS.
  float v = h < 4 ? y : (h == 12 || h == 14 ? x : z);
  return ((h & 1) == 0 ? u : -u) + ((h & 2) == 0 ? v : -v);
}

float Noise(double iz, double iy, double ix) {
  double fx = floor(ix), fy = floor(iy), fz = floor(iz);
  int X = (int)fx & 255,                  // FIND UNIT CUBE THAT
      Y = (int)fy & 255,                  // CONTAINS POINT.
      Z = (int)fz & 255;
  float x = (float)(ix - fx);                                // FIND RELATIVE X,Y,Z
  float y = (float)(iy - fy);                                // OF POINT IN CUBE.
  float z = (float)(iz - fz);
  float u = fade(x);                           // COMPUTE FADE CURVES
  float v = fade(y);                           // FOR EACH OF X,Y,Z.
  float w = fade(z);
  int A  = p[X  ]+Y, B  = p[X+1]+Y;
  int AA = p[A]+Z,   AB = p[A+1]+Z;             // HASH COORDINATES OF
  int BA = p[B]+Z,   BB = p[B+1]+Z;             // THE 8 CUBE CORNERS,
  return lerp(w, lerp(v, lerp(u, grad(p[AA  ], x  , y  , z   ),   // AND ADD
                                 grad(p[BA  ], x-1, y  , z   )),  // BLENDED
                         lerp(u, grad(p[AB  ], x  , y-1, z   ),   // RESULTS
                                 grad(p[BB  ], x-1, y-1, z   ))), // FROM  8
                 lerp(v, lerp(u, grad(p[AA+1], x  , y  , z-1 ),   // CORNERS
                                 grad(p[BA+1], x-1, y  , z-1 )),  // OF CUBE
                         lerp(u, grad(p[AB+1], x  , y-1, z-1 ),
                                 grad(p[BB+1], x-1, y-1, z-1 ))));
}