package net.minecraft.world.level.levelgen.synth;

import it.unimi.dsi.fastutil.ints.IntRBTreeSet;
import it.unimi.dsi.fastutil.ints.IntSortedSet;
import java.util.List;
import net.minecraft.util.RandomSource;
import net.minecraft.world.level.levelgen.LegacyRandomSource;
import net.minecraft.world.level.levelgen.WorldgenRandom;
import org.jspecify.annotations.Nullable;

public class PerlinSimplexNoise {
	private final @Nullable SimplexNoise[] noiseLevels;
	private final double highestFreqValueFactor;
	private final double highestFreqInputFactor;

	public PerlinSimplexNoise(final RandomSource random, final List<Integer> octaveSet) {
		this(random, new IntRBTreeSet(octaveSet));
	}

	private PerlinSimplexNoise(final RandomSource random, final IntSortedSet octaveSet) {
		if (octaveSet.isEmpty()) {
			throw new IllegalArgumentException("Need some octaves!");
		}

		int lowFreqOctaves = -octaveSet.firstInt();
		int highFreqOctaves = octaveSet.lastInt();
		int octaves = lowFreqOctaves + highFreqOctaves + 1;
		if (octaves < 1) {
			throw new IllegalArgumentException("Total number of octaves needs to be >= 1");
		}

		SimplexNoise zeroOctave = new SimplexNoise(random);
		int zeroOctaveIndex = highFreqOctaves;
		this.noiseLevels = new SimplexNoise[octaves];
		if (zeroOctaveIndex >= 0 && zeroOctaveIndex < octaves && octaveSet.contains(0)) {
			this.noiseLevels[zeroOctaveIndex] = zeroOctave;
		}

		for (int i = zeroOctaveIndex + 1; i < octaves; i++) {
			if (i >= 0 && octaveSet.contains(zeroOctaveIndex - i)) {
				this.noiseLevels[i] = new SimplexNoise(random);
			} else {
				random.consumeCount(262);
			}
		}

		if (highFreqOctaves > 0) {
			long positiveOctaveSeed = (long)(zeroOctave.getValue(zeroOctave.xo, zeroOctave.yo, zeroOctave.zo) * 9.223372E18F);
			RandomSource highFreqRandom = new WorldgenRandom(new LegacyRandomSource(positiveOctaveSeed));

			for (int i = zeroOctaveIndex - 1; i >= 0; i--) {
				if (i < octaves && octaveSet.contains(zeroOctaveIndex - i)) {
					this.noiseLevels[i] = new SimplexNoise(highFreqRandom);
				} else {
					highFreqRandom.consumeCount(262);
				}
			}
		}

		this.highestFreqInputFactor = Math.pow(2.0, highFreqOctaves);
		this.highestFreqValueFactor = 1.0 / (Math.pow(2.0, octaves) - 1.0);
	}

	public double getValue(final double x, final double y, final boolean useNoiseStart) {
		double value = 0.0;
		double factor = this.highestFreqInputFactor;
		double valueFactor = this.highestFreqValueFactor;

		for (SimplexNoise noiseLevel : this.noiseLevels) {
			if (noiseLevel != null) {
				value += noiseLevel.getValue(x * factor + (useNoiseStart ? noiseLevel.xo : 0.0), y * factor + (useNoiseStart ? noiseLevel.yo : 0.0)) * valueFactor;
			}

			factor /= 2.0;
			valueFactor *= 2.0;
		}

		return value;
	}
}