package net.minecraft.world.level.chunk.storage;

import com.google.common.annotations.VisibleForTesting;
import it.unimi.dsi.fastutil.ints.IntArraySet;
import it.unimi.dsi.fastutil.ints.IntCollection;
import it.unimi.dsi.fastutil.ints.IntSet;
import java.util.BitSet;

/**
 * Keeps track of which parts of a region file are used and which parts are free.
 */
public class RegionBitmap {
	private final BitSet used = new BitSet();

	/**
	 * Marks a range of 4 KiB sectors relative to the region file as used.
	 * 
	 * @param sectorOffset The first sector in the range.
	 * @param sectorCount The amount of sectors in the range.
	 */
	public void force(int sectorOffset, int sectorCount) {
		this.used.set(sectorOffset, sectorOffset + sectorCount);
	}

	/**
	 * Marks a range of 4 KiB sectors relative to the region file as not used.
	 * 
	 * @param sectorOffset The first sector in the range.
	 * @param sectorCount The amount of sectors in the range.
	 */
	public void free(int sectorOffset, int sectorCount) {
		this.used.clear(sectorOffset, sectorOffset + sectorCount);
	}

	/**
	 * Gets a valid offset inside the region file with enough space to store the given amount of sectors and marks that space as used.
	 */
	public int allocate(int sectorCount) {
		int i = 0;

		while (true) {
			int j = this.used.nextClearBit(i);
			int k = this.used.nextSetBit(j);
			if (k == -1 || k - j >= sectorCount) {
				this.force(j, sectorCount);
				return j;
			}

			i = k;
		}
	}

	@VisibleForTesting
	public IntSet getUsed() {
		return (IntSet)this.used.stream().collect(IntArraySet::new, IntCollection::add, IntCollection::addAll);
	}
}