/*
This file is part of libnoise-dotnet.
libnoise-dotnet is free software: you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
libnoise-dotnet is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with libnoise-dotnet.  If not, see <http://www.gnu.org/licenses/>.
Simplex Noise in 2D, 3D and 4D. Based on the example code of this paper:
http://staffwww.itn.liu.se/~stegu/simplexnoise/simplexnoise.pdf
From Stefan Gustavson, Linkping University, Sweden (stegu at itn dot liu dot se)
From Karsten Schmidt (slight optimizations & restructuring)
Some changes by Sebastian Lague for use in a tutorial series.
*/

/*
 * Noise module that outputs 3-dimensional Simplex Perlin noise.
 * This algorithm has a computational cost of O(n+1) where n is the dimension.
 * 
 * This noise module outputs values that usually range from
 * -1.0 to +1.0, but there are no guarantees that all output values will exist within that range.
*/

using System;
public class LibNoise {
  #region Values
  /// Initial permutation table
  static readonly int[] Source = {
            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
        };

  const int RandomSize = 256;
  const double Sqrt3 = 1.7320508075688772935;
  const double Sqrt5 = 2.2360679774997896964;
  int[] _random;

  /// Skewing and unskewing factors for 2D, 3D and 4D, 
  /// some of them pre-multiplied.
  const double F2 = 0.5 * (Sqrt3 - 1.0);

  const double G2 = (3.0 - Sqrt3) / 6.0;
  const double G22 = G2 * 2.0 - 1;

  const double F3 = 1.0 / 3.0;
  const double G3 = 1.0 / 6.0;

  const double F4 = (Sqrt5 - 1.0) / 4.0;
  const double G4 = (5.0 - Sqrt5) / 20.0;
  const double G42 = G4 * 2.0;
  const double G43 = G4 * 3.0;
  const double G44 = G4 * 4.0 - 1.0;

  /// <summary>
  /// Gradient vectors for 3D (pointing to mid points of all edges of a unit
  /// cube)
  /// </summary>
  static readonly int[][] Grad3 =
  {
        new[] {1, 1, 0}, new[] {-1, 1, 0}, new[] {1, -1, 0},
        new[] {-1, -1, 0}, new[] {1, 0, 1}, new[] {-1, 0, 1},
        new[] {1, 0, -1}, new[] {-1, 0, -1}, new[] {0, 1, 1},
        new[] {0, -1, 1}, new[] {0, 1, -1}, new[] {0, -1, -1}
    };
  #endregion

  public LibNoise() {
    Randomize(0);
  }

  public LibNoise(int seed) {
    Randomize(seed);
  }


  /// <summary>
  /// Generates value, typically in range [-1, 1]
  /// </summary>
  public float Evaluate(UnityEngine.Vector3 point) {
    double x = point.x;
    double y = point.y;
    double z = point.z;
    double n0 = 0, n1 = 0, n2 = 0, n3 = 0;

    // Noise contributions from the four corners
    // Skew the input space to determine which simplex cell we're in
    double s = (x + y + z) * F3;

    // for 3D
    int i = FastFloor(x + s);
    int j = FastFloor(y + s);
    int k = FastFloor(z + s);

    double t = (i + j + k) * G3;

    // The x,y,z distances from the cell origin
    double x0 = x - (i - t);
    double y0 = y - (j - t);
    double z0 = z - (k - t);

    // For the 3D case, the simplex shape is a slightly irregular tetrahedron.
    // Determine which simplex we are in.
    // Offsets for second corner of simplex in (i,j,k)
    int i1, j1, k1;

    // coords
    int i2, j2, k2; // Offsets for third corner of simplex in (i,j,k) coords

    if (x0 >= y0) {
      if (y0 >= z0) {
        // X Y Z order
        i1 = 1;
        j1 = 0;
        k1 = 0;
        i2 = 1;
        j2 = 1;
        k2 = 0;
      } else if (x0 >= z0) {
        // X Z Y order
        i1 = 1;
        j1 = 0;
        k1 = 0;
        i2 = 1;
        j2 = 0;
        k2 = 1;
      } else {
        // Z X Y order
        i1 = 0;
        j1 = 0;
        k1 = 1;
        i2 = 1;
        j2 = 0;
        k2 = 1;
      }
    } else {
      // x0 < y0
      if (y0 < z0) {
        // Z Y X order
        i1 = 0;
        j1 = 0;
        k1 = 1;
        i2 = 0;
        j2 = 1;
        k2 = 1;
      } else if (x0 < z0) {
        // Y Z X order
        i1 = 0;
        j1 = 1;
        k1 = 0;
        i2 = 0;
        j2 = 1;
        k2 = 1;
      } else {
        // Y X Z order
        i1 = 0;
        j1 = 1;
        k1 = 0;
        i2 = 1;
        j2 = 1;
        k2 = 0;
      }
    }

    // A step of (1,0,0) in (i,j,k) means a step of (1-c,-c,-c) in (x,y,z),
    // a step of (0,1,0) in (i,j,k) means a step of (-c,1-c,-c) in (x,y,z),
    // and
    // a step of (0,0,1) in (i,j,k) means a step of (-c,-c,1-c) in (x,y,z),
    // where c = 1/6.

    // Offsets for second corner in (x,y,z) coords
    double x1 = x0 - i1 + G3;
    double y1 = y0 - j1 + G3;
    double z1 = z0 - k1 + G3;

    // Offsets for third corner in (x,y,z)
    double x2 = x0 - i2 + F3;
    double y2 = y0 - j2 + F3;
    double z2 = z0 - k2 + F3;

    // Offsets for last corner in (x,y,z)
    double x3 = x0 - 0.5;
    double y3 = y0 - 0.5;
    double z3 = z0 - 0.5;

    // Work out the hashed gradient indices of the four simplex corners
    int ii = i & 0xff;
    int jj = j & 0xff;
    int kk = k & 0xff;

    // Calculate the contribution from the four corners
    double t0 = 0.6 - x0 * x0 - y0 * y0 - z0 * z0;
    if (t0 > 0) {
      t0 *= t0;
      int gi0 = _random[ii + _random[jj + _random[kk]]] % 12;
      n0 = t0 * t0 * Dot(Grad3[gi0], x0, y0, z0);
    }

    double t1 = 0.6 - x1 * x1 - y1 * y1 - z1 * z1;
    if (t1 > 0) {
      t1 *= t1;
      int gi1 = _random[ii + i1 + _random[jj + j1 + _random[kk + k1]]] % 12;
      n1 = t1 * t1 * Dot(Grad3[gi1], x1, y1, z1);
    }

    double t2 = 0.6 - x2 * x2 - y2 * y2 - z2 * z2;
    if (t2 > 0) {
      t2 *= t2;
      int gi2 = _random[ii + i2 + _random[jj + j2 + _random[kk + k2]]] % 12;
      n2 = t2 * t2 * Dot(Grad3[gi2], x2, y2, z2);
    }

    double t3 = 0.6 - x3 * x3 - y3 * y3 - z3 * z3;
    if (t3 > 0) {
      t3 *= t3;
      int gi3 = _random[ii + 1 + _random[jj + 1 + _random[kk + 1]]] % 12;
      n3 = t3 * t3 * Dot(Grad3[gi3], x3, y3, z3);
    }

    // Add contributions from each corner to get the final noise value.
    // The result is scaled to stay just inside [-1,1]
    return (float)(n0 + n1 + n2 + n3) * 32;
  }


  void Randomize(int seed) {
    _random = new int[RandomSize * 2];

    if (seed != 0) {
      // Shuffle the array using the given seed
      // Unpack the seed into 4 bytes then perform a bitwise XOR operation
      // with each byte
      var F = new byte[4];
      UnpackLittleUint32(seed, ref F);

      for (int i = 0; i < Source.Length; i++) {
        _random[i] = Source[i] ^ F[0];
        _random[i] ^= F[1];
        _random[i] ^= F[2];
        _random[i] ^= F[3];

        _random[i + RandomSize] = _random[i];
      }

    } else {
      for (int i = 0; i < RandomSize; i++)
        _random[i + RandomSize] = _random[i] = Source[i];
    }
  }

  static double Dot(int[] g, double x, double y, double z, double t) {
    return g[0] * x + g[1] * y + g[2] * z + g[3] * t;
  }

  static double Dot(int[] g, double x, double y, double z) {
    return g[0] * x + g[1] * y + g[2] * z;
  }

  static double Dot(int[] g, double x, double y) {
    return g[0] * x + g[1] * y;
  }

  static int FastFloor(double x) {
    return x >= 0 ? (int)x : (int)x - 1;
  }

  /// <summary>
  /// Unpack the given integer (int32) to an array of 4 bytes  in little endian format.
  /// If the length of the buffer is too smal, it wil be resized.
  /// </summary>
  /// <param name="value">The value.</param>
  /// <param name="buffer">The output buffer.</param>
  static byte[] UnpackLittleUint32(int value, ref byte[] buffer) {
    if (buffer.Length < 4)
      Array.Resize(ref buffer, 4);

    buffer[0] = (byte)(value & 0x00ff);
    buffer[1] = (byte)((value & 0xff00) >> 8);
    buffer[2] = (byte)((value & 0x00ff0000) >> 16);
    buffer[3] = (byte)((value & 0xff000000) >> 24);

    return buffer;
  }

}