package com.mojang.blaze3d.resource;

import com.google.common.annotations.VisibleForTesting;
import java.util.ArrayDeque;
import java.util.Collection;
import java.util.Deque;
import java.util.Iterator;
import net.fabricmc.api.EnvType;
import net.fabricmc.api.Environment;

@Environment(EnvType.CLIENT)
public class CrossFrameResourcePool implements GraphicsResourceAllocator, AutoCloseable {
	private final int framesToKeepResource;
	private final Deque<CrossFrameResourcePool.ResourceEntry<?>> pool = new ArrayDeque();

	public CrossFrameResourcePool(final int framesToKeepResource) {
		this.framesToKeepResource = framesToKeepResource;
	}

	public void endFrame() {
		Iterator<? extends CrossFrameResourcePool.ResourceEntry<?>> iterator = this.pool.iterator();

		while (iterator.hasNext()) {
			CrossFrameResourcePool.ResourceEntry<?> entry = (CrossFrameResourcePool.ResourceEntry<?>)iterator.next();
			if (entry.framesToLive-- == 0) {
				entry.close();
				iterator.remove();
			}
		}
	}

	@Override
	public <T> T acquire(final ResourceDescriptor<T> descriptor) {
		T resource = this.acquireWithoutPreparing(descriptor);
		descriptor.prepare(resource);
		return resource;
	}

	private <T> T acquireWithoutPreparing(final ResourceDescriptor<T> descriptor) {
		Iterator<? extends CrossFrameResourcePool.ResourceEntry<?>> iterator = this.pool.iterator();

		while (iterator.hasNext()) {
			CrossFrameResourcePool.ResourceEntry<?> entry = (CrossFrameResourcePool.ResourceEntry<?>)iterator.next();
			if (descriptor.canUsePhysicalResource(entry.descriptor)) {
				iterator.remove();
				return (T)entry.value;
			}
		}

		return descriptor.allocate();
	}

	@Override
	public <T> void release(final ResourceDescriptor<T> descriptor, final T resource) {
		this.pool.addFirst(new CrossFrameResourcePool.ResourceEntry<>(descriptor, resource, this.framesToKeepResource));
	}

	public void clear() {
		this.pool.forEach(CrossFrameResourcePool.ResourceEntry::close);
		this.pool.clear();
	}

	public void close() {
		this.clear();
	}

	@VisibleForTesting
	protected Collection<CrossFrameResourcePool.ResourceEntry<?>> entries() {
		return this.pool;
	}

	@Environment(EnvType.CLIENT)
	@VisibleForTesting
	protected static final class ResourceEntry<T> implements AutoCloseable {
		private final ResourceDescriptor<T> descriptor;
		private final T value;
		private int framesToLive;

		private ResourceEntry(final ResourceDescriptor<T> descriptor, final T value, final int framesToLive) {
			this.descriptor = descriptor;
			this.value = value;
			this.framesToLive = framesToLive;
		}

		public void close() {
			this.descriptor.free(this.value);
		}
	}
}