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

function SimplexNoise(random) {
    if (!random) random = Math.random;
    this.p = new Uint8Array(256);
    this.perm = new Uint8Array(512);
    this.permMod12 = new Uint8Array(512);
    for (var i = 0; i < 256; i++) {
        this.p[i] = random() * 256;
    }
    for (i = 0; i < 512; i++) {
        this.perm[i] = this.p[i & 255];
        this.permMod12[i] = this.perm[i] % 12;
    }
}
SimplexNoise.prototype = {
    grad3: new Float32Array([1, 1, 0,
                            - 1, 1, 0,
                            1, - 1, 0,

                            - 1, - 1, 0,
                            1, 0, 1,
                            - 1, 0, 1,

                            1, 0, - 1,
                            - 1, 0, - 1,
                            0, 1, 1,

                            0, - 1, 1,
                            0, 1, - 1,
                            0, - 1, - 1]),
    // 3D simplex noise
    noise3D: function (xin, yin, zin) {
        var permMod12 = this.permMod12,
            perm = this.perm,
            grad3 = this.grad3;
        var n0, n1, n2, n3; // Noise contributions from the four corners
        // Skew the input space to determine which simplex cell we're in
        var s = (xin + yin + zin) * F3; // Very nice and simple skew factor for 3D
        var i = Math.floor(xin + s);
        var j = Math.floor(yin + s);
        var k = Math.floor(zin + s);
        var t = (i + j + k) * G3;
        var X0 = i - t; // Unskew the cell origin back to (x,y,z) space
        var Y0 = j - t;
        var Z0 = k - t;
        var x0 = xin - X0; // The x,y,z distances from the cell origin
        var y0 = yin - Y0;
        var z0 = zin - Z0;
        // For the 3D case, the simplex shape is a slightly irregular tetrahedron.
        // Determine which simplex we are in.
        var i1, j1, k1; // Offsets for second corner of simplex in (i,j,k) coords
        var 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.
        var x1 = x0 - i1 + G3; // Offsets for second corner in (x,y,z) coords
        var y1 = y0 - j1 + G3;
        var z1 = z0 - k1 + G3;
        var x2 = x0 - i2 + 2.0 * G3; // Offsets for third corner in (x,y,z) coords
        var y2 = y0 - j2 + 2.0 * G3;
        var z2 = z0 - k2 + 2.0 * G3;
        var x3 = x0 - 1.0 + 3.0 * G3; // Offsets for last corner in (x,y,z) coords
        var y3 = y0 - 1.0 + 3.0 * G3;
        var z3 = z0 - 1.0 + 3.0 * G3;
        // Work out the hashed gradient indices of the four simplex corners
        var ii = i & 255;
        var jj = j & 255;
        var kk = k & 255;
        // Calculate the contribution from the four corners
        var t0 = 0.6 - x0 * x0 - y0 * y0 - z0 * z0;
        if (t0 < 0) n0 = 0.0;
        else {
            var gi0 = permMod12[ii + perm[jj + perm[kk]]] * 3;
            t0 *= t0;
            n0 = t0 * t0 * (grad3[gi0] * x0 + grad3[gi0 + 1] * y0 + grad3[gi0 + 2] * z0);
        }
        var t1 = 0.6 - x1 * x1 - y1 * y1 - z1 * z1;
        if (t1 < 0) n1 = 0.0;
        else {
            var gi1 = permMod12[ii + i1 + perm[jj + j1 + perm[kk + k1]]] * 3;
            t1 *= t1;
            n1 = t1 * t1 * (grad3[gi1] * x1 + grad3[gi1 + 1] * y1 + grad3[gi1 + 2] * z1);
        }
        var t2 = 0.6 - x2 * x2 - y2 * y2 - z2 * z2;
        if (t2 < 0) n2 = 0.0;
        else {
            var gi2 = permMod12[ii + i2 + perm[jj + j2 + perm[kk + k2]]] * 3;
            t2 *= t2;
            n2 = t2 * t2 * (grad3[gi2] * x2 + grad3[gi2 + 1] * y2 + grad3[gi2 + 2] * z2);
        }
        var t3 = 0.6 - x3 * x3 - y3 * y3 - z3 * z3;
        if (t3 < 0) n3 = 0.0;
        else {
            var gi3 = permMod12[ii + 1 + perm[jj + 1 + perm[kk + 1]]] * 3;
            t3 *= t3;
            n3 = t3 * t3 * (grad3[gi3] * x3 + grad3[gi3 + 1] * y3 + grad3[gi3 + 2] * z3);
        }
        // Add contributions from each corner to get the final noise value.
        // The result is scaled to stay just inside [-1,1]
        return 32.0 * (n0 + n1 + n2 + n3);
    },
};

export default SimplexNoise
