package ninja.bytecode.iris.util;

import java.util.Random;

public class PerlinNoise extends BasePerlinNoiseGenerator
{

	/**
	 * Creates an instance using the given PRNG.
	 * 
	 * @param rand
	 *            the PRNG used to generate the seed permutation
	 */
	public PerlinNoise(Random rand)
	{
		offsetX = rand.nextDouble() * 256;
		offsetY = rand.nextDouble() * 256;
		offsetZ = rand.nextDouble() * 256;
		// The only reason why I'm re-implementing the constructor code is that I've
		// read
		// on at least 3 different sources that the permutation table should initially
		// be
		// populated with indices.
		// "The permutation table is his answer to the issue of random numbers.
		// First take an array of decent length, usually 256 values. Fill it
		// sequentially with each
		// number in that range: so index 1 gets 1, index 8 gets 8, index 251 gets 251,
		// etc...
		// Then randomly shuffle the values so you have a table of 256 random values,
		// but only
		// contains the values between 0 and 255."
		// source: https://code.google.com/p/fractalterraingeneration/wiki/Perlin_Noise
		for(int i = 0; i < 256; i++)
		{
			perm[i] = i;
		}
		for(int i = 0; i < 256; i++)
		{
			int pos = rand.nextInt(256 - i) + i;
			int old = perm[i];
			perm[i] = perm[pos];
			perm[pos] = old;
			perm[i + 256] = perm[i];
		}
	}

	public static int floor(double x)
	{
		int floored = (int) x;
		return x < floored ? floored - 1 : floored;
	}

	/**
	 * Generates a rectangular section of this generator's noise.
	 *
	 * @param noise
	 *            the output of the previous noise layer
	 * @param x
	 *            the X offset
	 * @param y
	 *            the Y offset
	 * @param z
	 *            the Z offset
	 * @param sizeX
	 *            the size on the X axis
	 * @param sizeY
	 *            the size on the Y axis
	 * @param sizeZ
	 *            the size on the Z axis
	 * @param scaleX
	 *            the X scale parameter
	 * @param scaleY
	 *            the Y scale parameter
	 * @param scaleZ
	 *            the Z scale parameter
	 * @param amplitude
	 *            the amplitude parameter
	 * @return {@code noise} with this layer of noise added
	 */
	public double[] getNoise(double[] noise, double x, double y, double z, int sizeX, int sizeY, int sizeZ, double scaleX, double scaleY, double scaleZ, double amplitude)
	{
		if(sizeY == 1)
		{
			return get2dNoise(noise, x, z, sizeX, sizeZ, scaleX, scaleZ, amplitude);
		}
		else
		{
			return get3dNoise(noise, x, y, z, sizeX, sizeY, sizeZ, scaleX, scaleY, scaleZ, amplitude);
		}
	}

	protected double[] get2dNoise(double[] noise, double x, double z, int sizeX, int sizeZ, double scaleX, double scaleZ, double amplitude)
	{
		int index = 0;
		for(int i = 0; i < sizeX; i++)
		{
			double dx = x + offsetX + i * scaleX;
			int floorX = floor(dx);
			int ix = floorX & 255;
			dx -= floorX;
			double fx = fade(dx);
			for(int j = 0; j < sizeZ; j++)
			{
				double dz = z + offsetZ + j * scaleZ;
				int floorZ = floor(dz);
				int iz = floorZ & 255;
				dz -= floorZ;
				double fz = fade(dz);
				// Hash coordinates of the square corners
				int a = perm[ix];
				int aa = perm[a] + iz;
				int b = perm[ix + 1];
				int ba = perm[b] + iz;
				double x1 = lerp(fx, grad(perm[aa], dx, 0, dz), grad(perm[ba], dx - 1, 0, dz));
				double x2 = lerp(fx, grad(perm[aa + 1], dx, 0, dz - 1), grad(perm[ba + 1], dx - 1, 0, dz - 1));
				noise[index++] += lerp(fz, x1, x2) * amplitude;
			}
		}
		return noise;
	}

	protected double[] get3dNoise(double[] noise, double x, double y, double z, int sizeX, int sizeY, int sizeZ, double scaleX, double scaleY, double scaleZ, double amplitude)
	{
		int n = -1;
		double x1 = 0;
		double x2 = 0;
		double x3 = 0;
		double x4 = 0;
		int index = 0;
		for(int i = 0; i < sizeX; i++)
		{
			double dx = x + offsetX + i * scaleX;
			int floorX = floor(dx);
			int ix = floorX & 255;
			dx -= floorX;
			double fx = fade(dx);
			for(int j = 0; j < sizeZ; j++)
			{
				double dz = z + offsetZ + j * scaleZ;
				int floorZ = floor(dz);
				int iz = floorZ & 255;
				dz -= floorZ;
				double fz = fade(dz);
				for(int k = 0; k < sizeY; k++)
				{
					double dy = y + offsetY + k * scaleY;
					int floorY = floor(dy);
					int iy = floorY & 255;
					dy -= floorY;
					double fy = fade(dy);
					if(k == 0 || iy != n)
					{
						n = iy;
						// Hash coordinates of the cube corners
						int a = perm[ix] + iy;
						int aa = perm[a] + iz;
						int ab = perm[a + 1] + iz;
						int b = perm[ix + 1] + iy;
						int ba = perm[b] + iz;
						int bb = perm[b + 1] + iz;
						x1 = lerp(fx, grad(perm[aa], dx, dy, dz), grad(perm[ba], dx - 1, dy, dz));
						x2 = lerp(fx, grad(perm[ab], dx, dy - 1, dz), grad(perm[bb], dx - 1, dy - 1, dz));
						x3 = lerp(fx, grad(perm[aa + 1], dx, dy, dz - 1), grad(perm[ba + 1], dx - 1, dy, dz - 1));
						x4 = lerp(fx, grad(perm[ab + 1], dx, dy - 1, dz - 1), grad(perm[bb + 1], dx - 1, dy - 1, dz - 1));
					}
					double y1 = lerp(fy, x1, x2);
					double y2 = lerp(fy, x3, x4);

					noise[index++] += lerp(fz, y1, y2) * amplitude;
				}
			}
		}
		return noise;
	}
}