using System;

namespace terrain
{
    public class Noise
    {
        public Noise(int seed)
        {
            var rand = new Random(seed);
            for (int i = 0; i < p.Length; i++)
                p[i] = (byte)rand.Next();
            for (int i = 0; i < 512; i++)
                perm[i] = p[i & 255];
        }
        // simplex noise in 2D, 3D and 4D
        private int[][] grad3 = new int[][] {
            new int[] {1,1,0}, new int[] {-1,1,0}, new int[] {1,-1,0}, new int[] {-1,-1,0},
            new int[] {1,0,1}, new int[] {-1,0,1}, new int[] {1,0,-1}, new int[] {-1,0,-1},
            new int[] {0,1,1}, new int[] {0,-1,1}, new int[] {0,1,-1}, new int[] {0,-1,-1}
        };

        private int[] p = {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};
        // To remove the need for index wrapping, double the permutation table length
        private int[] perm = new int[512];

        // This method is a *lot* faster than using (int)Math.floor(x)
        private int fastfloor(double x)
        {
            return x > 0 ? (int)x : (int)x - 1;
        }

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

        public float GetNoise(double pX, double pY, double pZ)
        {
            double n0, n1, n2, n3; // Noise contributions from the four corners
            // Skew the input space to determine which simplex cell we're in
            double F3 = 1.0 / 3.0;
            double s = (pX + pY + pZ) * F3; // Very nice and simple skew factor for 3D
            int i = fastfloor(pX + s);
            int j = fastfloor(pY + s);
            int k = fastfloor(pZ + s);
            double G3 = 1.0 / 6.0; // Very nice and simple unskew factor, too
            double t = (i + j + k) * G3;
            double X0 = i - t; // Unskew the cell origin back to (x,y,z) space
            double Y0 = j - t;
            double Z0 = k - t;
            double x0 = pX - X0; // The x,y,z distances from the cell origin
            double y0 = pY - Y0;
            double z0 = pZ - Z0;
            // For the 3D case, the simplex shape is a slightly irregular tetrahedron.
            // Determine which simplex we are in.
            int i1, j1, k1; // Offsets for second corner of simplex in (i,j,k) coords
            int i2, j2, k2; // Offsets for third corner of simplex in (i,j,k) coords
            if (x0 >= y0)
            {
                if (y0 >= z0)
                {
                    i1 = 1;
                    j1 = 0;
                    k1 = 0;
                    i2 = 1;
                    j2 = 1;
                    k2 = 0;
                } // X Y Z order
                else if (x0 >= z0)
                {
                    i1 = 1;
                    j1 = 0;
                    k1 = 0;
                    i2 = 1;
                    j2 = 0;
                    k2 = 1;
                } // X Z Y order
                else
                {
                    i1 = 0;
                    j1 = 0;
                    k1 = 1;
                    i2 = 1;
                    j2 = 0;
                    k2 = 1;
                } // Z X Y order
            }
            else
            { // x0<y0
                if (y0 < z0)
                {
                    i1 = 0;
                    j1 = 0;
                    k1 = 1;
                    i2 = 0;
                    j2 = 1;
                    k2 = 1;
                } // Z Y X order
                else if (x0 < z0)
                {
                    i1 = 0;
                    j1 = 1;
                    k1 = 0;
                    i2 = 0;
                    j2 = 1;
                    k2 = 1;
                } // Y Z X order
                else
                {
                    i1 = 0;
                    j1 = 1;
                    k1 = 0;
                    i2 = 1;
                    j2 = 1;
                    k2 = 0;
                } // Y X Z order
            }
            // 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.

            double x1 = x0 - i1 + G3; // Offsets for second corner in (x,y,z) coords
            double y1 = y0 - j1 + G3;
            double z1 = z0 - k1 + G3;
            double x2 = x0 - i2 + 2.0 * G3; // Offsets for third corner in (x,y,z) coords
            double y2 = y0 - j2 + 2.0 * G3;
            double z2 = z0 - k2 + 2.0 * G3;
            double x3 = x0 - 1.0 + 3.0 * G3; // Offsets for last corner in (x,y,z) coords
            double y3 = y0 - 1.0 + 3.0 * G3;
            double z3 = z0 - 1.0 + 3.0 * G3;
            // Work out the hashed gradient indices of the four simplex corners
            int ii = i & 255;
            int jj = j & 255;
            int kk = k & 255;
            int gi0 = perm[ii + perm[jj + perm[kk]]] % 12;
            int gi1 = perm[ii + i1 + perm[jj + j1 + perm[kk + k1]]] % 12;
            int gi2 = perm[ii + i2 + perm[jj + j2 + perm[kk + k2]]] % 12;
            int gi3 = perm[ii + 1 + perm[jj + 1 + perm[kk + 1]]] % 12;
            // Calculate the contribution from the four corners
            double t0 = 0.6 - x0 * x0 - y0 * y0 - z0 * z0;
            if (t0 < 0)
                n0 = 0.0;
            else
            {
                t0 *= t0;
                n0 = t0 * t0 * dot(grad3[gi0], x0, y0, z0);
            }
            double t1 = 0.6 - x1 * x1 - y1 * y1 - z1 * z1;
            if (t1 < 0)
                n1 = 0.0;
            else
            {
                t1 *= t1;
                n1 = t1 * t1 * dot(grad3[gi1], x1, y1, z1);
            }
            double t2 = 0.6 - x2 * x2 - y2 * y2 - z2 * z2;
            if (t2 < 0)
                n2 = 0.0;
            else
            {
                t2 *= t2;
                n2 = t2 * t2 * dot(grad3[gi2], x2, y2, z2);
            }
            double t3 = 0.6 - x3 * x3 - y3 * y3 - z3 * z3;
            if (t3 < 0)
                n3 = 0.0;
            else
            {
                t3 *= t3;
                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] - now [0, 1]
            return (32.0f * (float)(n0 + n1 + n2 + n3) + 1) * 0.5f;
        }
    }
}