/*
 *     FileSponge
 *     Copyright (C) 2021 Andrea Cavalli
 *
 *     This program is free software: you can redistribute it and/or modify
 *     it under the terms of the GNU General Public License as published by
 *     the Free Software Foundation, either version 3 of the License, or
 *     (at your option) any later version.
 *
 *     This program is distributed in the hope that it will be useful,
 *     but WITHOUT ANY WARRANTY; without even the implied warranty of
 *     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *     GNU General Public License for more details.
 *
 *     You should have received a copy of the GNU General Public License
 *     along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */

package org.warp.filesponge;

import static org.warp.filesponge.FileSponge.BLOCK_SIZE;

import com.google.common.primitives.Ints;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.PooledByteBufAllocator;
import io.netty.buffer.Unpooled;
import io.netty.util.ReferenceCounted;
import it.cavallium.dbengine.database.Column;
import it.cavallium.dbengine.database.LLDatabaseConnection;
import it.cavallium.dbengine.database.LLDictionary;
import it.cavallium.dbengine.database.LLDictionaryResultType;
import it.cavallium.dbengine.database.LLKeyValueDatabase;
import it.cavallium.dbengine.database.UpdateMode;
import it.cavallium.dbengine.database.UpdateReturnMode;
import it.cavallium.dbengine.database.disk.LLLocalDictionary.ReleasableSlice;
import it.unimi.dsi.fastutil.booleans.BooleanArrayList;
import java.nio.ByteBuffer;
import java.util.Arrays;
import java.util.List;
import java.util.Optional;
import lombok.AccessLevel;
import lombok.AllArgsConstructor;
import org.jetbrains.annotations.Nullable;
import org.warp.filesponge.DiskMetadata.DiskMetadataSerializer;
import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;
import reactor.core.scheduler.Schedulers;
import reactor.util.function.Tuple2;
import reactor.util.function.Tuples;

public class DiskCache implements URLsDiskHandler, URLsWriter {

	private final DiskMetadataSerializer diskMetadataSerializer;

	private final LLKeyValueDatabase db;
	private final LLDictionary fileContent;
	private final LLDictionary fileMetadata;

	public DiskCache(LLKeyValueDatabase db, LLDictionary fileContent, LLDictionary fileMetadata) {
		this.db = db;
		this.fileContent = fileContent;
		this.fileMetadata = fileMetadata;
		this.diskMetadataSerializer = new DiskMetadataSerializer(db.getAllocator());
	}

	public static Mono<DiskCache> open(LLDatabaseConnection databaseConnection, String dbName, boolean lowMemory) {
		return databaseConnection
				.getDatabase(dbName, List.of(Column.dictionary("file-content"), Column.dictionary("file-metadata")), lowMemory, false)
				.flatMap(db -> Mono.zip(
						Mono.just(db).single(),
						db.getDictionary("file-content", UpdateMode.ALLOW).single(),
						db.getDictionary("file-metadata", UpdateMode.ALLOW).single()
				))
				.map(tuple -> new DiskCache(tuple.getT1(), tuple.getT2(), tuple.getT3()))
				.single();
	}

	@Override
	public Mono<Void> writeMetadata(URL url, Metadata metadata) {
		return Mono
				.using(
						() -> url.getSerializer(db.getAllocator()).serialize(url),
						key -> fileMetadata
								.update(key.retain(), oldValue -> {
									if (oldValue != null) {
										return oldValue;
									} else {
										return diskMetadataSerializer.serialize(new DiskMetadata(
												metadata.getSize(),
												BooleanArrayList.wrap(new boolean[DiskMetadata.getBlocksCount(metadata.getSize(), BLOCK_SIZE)])
										));
									}
								}, UpdateReturnMode.NOTHING),
						ReferenceCounted::release
				)
				.then();
	}

	@Override
	public Mono<Void> writeContentBlock(URL url, DataBlock dataBlock) {
		return Mono
				.fromCallable(dataBlock::getData)
				.subscribeOn(Schedulers.boundedElastic())
				.flatMap(bytes -> Mono
						.using(
								() -> getBlockKey(url, dataBlock.getId()),
								key -> fileContent
										.put(key.retain(), bytes, LLDictionaryResultType.VOID),
								ReferenceCounted::release
						)
						.doOnNext(ReferenceCounted::release)
						.then()
				)
				.then(Mono
						.using(
								() -> url.getSerializer(db.getAllocator()).serialize(url),
								key -> fileMetadata.update(key.retain(), prevBytes -> {
									@Nullable DiskMetadata result;
									if (prevBytes != null) {
										DiskMetadata prevMeta = diskMetadataSerializer.deserialize(prevBytes);
										if (!prevMeta.getDownloadedBlocks().getBoolean(dataBlock.getId())) {
											BooleanArrayList bal = prevMeta.getDownloadedBlocks().clone();
											bal.set(dataBlock.getId(), true);
											result = new DiskMetadata(prevMeta.getSize(), bal);
										} else {
											result = prevMeta;
										}
									} else {
										result = null;
									}
									if (result != null) {
										return diskMetadataSerializer.serialize(result);
									} else {
										return null;
									}
								}, UpdateReturnMode.NOTHING),
								ReferenceCounted::release
						)
				)
				.then();
	}

	@Override
	public Flux<DataBlock> requestContent(URL url) {
		return requestDiskMetadata(url)
				.filter(DiskMetadata::isDownloadedFully)
				.flatMapMany(meta -> Flux.fromIterable(meta.getDownloadedBlocks())
						.index()
						// Get only downloaded blocks
						.filter(Tuple2::getT2)
						.flatMapSequential(blockMeta -> {
							int blockId = Math.toIntExact(blockMeta.getT1());
							boolean downloaded = blockMeta.getT2();
							if (!downloaded) {
								return Mono.<DataBlock>empty();
							}
							return Mono
									.using(
											() -> getBlockKey(url, blockId),
											key -> fileContent.get(null, key.retain()),
											ReferenceCounted::release
									)
									.map(data -> {
										try {
											int blockOffset = getBlockOffset(blockId);
											int blockLength = data.readableBytes();
											if (blockOffset + blockLength >= meta.getSize()) {
												if (blockOffset + blockLength > meta.getSize()) {
													throw new IllegalStateException("Overflowed data size");
												}
											} else {
												// Intermediate blocks must be of max size
												assert data.readableBytes() == BLOCK_SIZE;
											}
											return new DataBlock(blockOffset, blockLength, data.retain());
										} finally {
											data.release();
										}
									});
						}));
	}

	private ByteBuf getBlockKey(URL url, int blockId) {
		ByteBuf urlBytes = url.getSerializer(db.getAllocator()).serialize(url);
		ByteBuf blockIdBytes = this.db.getAllocator().directBuffer(Integer.BYTES, Integer.BYTES);
		blockIdBytes.writeInt(blockId);
		return Unpooled.wrappedBuffer(urlBytes, blockIdBytes);
	}

	private static int getBlockOffset(int blockId) {
		return blockId * BLOCK_SIZE;
	}

	@Override
	public Mono<DiskMetadata> requestDiskMetadata(URL url) {
		return Mono
				.using(
						() -> url.getSerializer(db.getAllocator()).serialize(url),
						key -> fileMetadata.get(null, key.retain()),
						ReferenceCounted::release
				)
				.map(diskMetadataSerializer::deserialize);
	}

	@Override
	public Mono<Metadata> requestMetadata(URL url) {
		return requestDiskMetadata(url)
				.map(DiskMetadata::asMetadata);
	}

	@Override
	public Mono<Tuple2<Metadata, Flux<DataBlock>>> request(URL url) {
		return Mono
				.using(
						() -> url.getSerializer(db.getAllocator()).serialize(url),
						key -> fileMetadata.get(null, key.retain()),
						ReferenceCounted::release
				)
				.map(diskMetadataSerializer::deserialize)
				.map(diskMeta -> {
					var meta = diskMeta.asMetadata();
					if (diskMeta.isDownloadedFully()) {
						return Tuples.of(meta, this.requestContent(url));
					} else {
						return Tuples.of(meta, Flux.empty());
					}
				});
	}

	public Mono<Void> close() {
		return db.close();
	}
}