package it.cavallium.dbengine.database.collections;

import io.netty.buffer.Unpooled;
import it.cavallium.dbengine.client.CompositeSnapshot;
import it.cavallium.dbengine.database.LLDictionary;
import it.cavallium.dbengine.database.LLRange;
import it.cavallium.dbengine.database.LLSnapshot;
import java.util.Arrays;
import java.util.Map;
import java.util.Map.Entry;
import org.jetbrains.annotations.Nullable;
import reactor.core.publisher.Flux;
import reactor.core.publisher.GroupedFlux;
import reactor.core.publisher.Mono;
import reactor.util.function.Tuples;

// todo: implement optimized methods
public class DatabaseMapDictionaryDeep<T, U, US extends DatabaseStage<U>> implements DatabaseStageMap<T, U, US> {

	public static final byte[] EMPTY_BYTES = new byte[0];
	protected final LLDictionary dictionary;
	protected final SubStageGetter<U, US> subStageGetter;
	protected final SerializerFixedBinaryLength<T> keySuffixSerializer;
	protected final byte[] keyPrefix;
	protected final int keySuffixLength;
	protected final int keyExtLength;
	protected final LLRange range;

	protected static byte[] firstKey(byte[] prefixKey, int prefixLength, int suffixLength, int extLength) {
		return fillKeySuffixAndExt(prefixKey, prefixLength, suffixLength, extLength, (byte) 0x00);
	}

	protected static byte[] lastKey(byte[] prefixKey, int prefixLength, int suffixLength, int extLength) {
		return fillKeySuffixAndExt(prefixKey, prefixLength, suffixLength, extLength, (byte) 0xFF);
	}

	protected static byte[] fillKeySuffixAndExt(byte[] prefixKey, int prefixLength, int suffixLength, int extLength, byte fillValue) {
		assert prefixKey.length == prefixLength;
		assert suffixLength > 0;
		assert extLength > 0;
		byte[] result = Arrays.copyOf(prefixKey, prefixLength + suffixLength + extLength);
		Arrays.fill(result, prefixLength, result.length, fillValue);
		return result;
	}

	protected static byte[] firstKey(byte[] prefixKey, byte[] suffixKey, int prefixLength, int suffixLength, int extLength) {
		return fillKeyExt(prefixKey, suffixKey, prefixLength, suffixLength, extLength, (byte) 0x00);
	}

	protected static byte[] lastKey(byte[] prefixKey, byte[] suffixKey, int prefixLength, int suffixLength, int extLength) {
		return fillKeyExt(prefixKey, suffixKey, prefixLength, suffixLength, extLength, (byte) 0xFF);
	}

	protected static byte[] fillKeyExt(byte[] prefixKey,
			byte[] suffixKey,
			int prefixLength,
			int suffixLength,
			int extLength,
			byte fillValue) {
		assert prefixKey.length == prefixLength;
		assert suffixKey.length == suffixLength;
		assert suffixLength > 0;
		assert extLength > 0;
		byte[] result = Arrays.copyOf(prefixKey, prefixLength + suffixLength + extLength);
		System.arraycopy(suffixKey, 0, result, prefixLength, suffixLength);
		Arrays.fill(result, prefixLength + suffixLength, result.length, fillValue);
		return result;
	}

	/**
	 * Use DatabaseMapDictionaryRange.simple instead
	 */
	@Deprecated
	public static <T, U> DatabaseMapDictionaryDeep<T, U, DatabaseStageEntry<U>> simple(LLDictionary dictionary,
			SubStageGetterSingle<U> subStageGetter,
			SerializerFixedBinaryLength<T> keySerializer) {
		return new DatabaseMapDictionaryDeep<>(dictionary, subStageGetter, keySerializer, EMPTY_BYTES, 0);
	}

	public static <T, U, US extends DatabaseStage<U>> DatabaseMapDictionaryDeep<T, U, US> deepTail(LLDictionary dictionary,
			SubStageGetter<U, US> subStageGetter,
			SerializerFixedBinaryLength<T> keySerializer,
			int keyExtLength) {
		return new DatabaseMapDictionaryDeep<>(dictionary, subStageGetter, keySerializer, EMPTY_BYTES, keyExtLength);
	}

	public static <T, U, US extends DatabaseStage<U>> DatabaseMapDictionaryDeep<T, U, US> deepIntermediate(LLDictionary dictionary,
			SubStageGetter<U, US> subStageGetter,
			SerializerFixedBinaryLength<T> keySuffixSerializer,
			byte[] prefixKey,
			int keyExtLength) {
		return new DatabaseMapDictionaryDeep<>(dictionary, subStageGetter, keySuffixSerializer, prefixKey, keyExtLength);
	}

	protected DatabaseMapDictionaryDeep(LLDictionary dictionary,
			SubStageGetter<U, US> subStageGetter,
			SerializerFixedBinaryLength<T> keySuffixSerializer,
			byte[] prefixKey,
			int keyExtLength) {
		this.dictionary = dictionary;
		this.subStageGetter = subStageGetter;
		this.keySuffixSerializer = keySuffixSerializer;
		this.keyPrefix = prefixKey;
		this.keySuffixLength = keySuffixSerializer.getSerializedBinaryLength();
		this.keyExtLength = keyExtLength;
		byte[] firstKey = firstKey(keyPrefix, keyPrefix.length, keySuffixLength, keyExtLength);
		byte[] lastKey = lastKey(keyPrefix, keyPrefix.length, keySuffixLength, keyExtLength);
		this.range = keyPrefix.length == 0 ? LLRange.all() : LLRange.of(firstKey, lastKey);
	}

	@SuppressWarnings("unused")
	protected boolean suffixKeyConsistency(int keySuffixLength) {
		return this.keySuffixLength == keySuffixLength;
	}

	@SuppressWarnings("unused")
	protected boolean extKeyConsistency(int keyExtLength) {
		return this.keyExtLength == keyExtLength;
	}

	@SuppressWarnings("unused")
	protected boolean suffixAndExtKeyConsistency(int keySuffixAndExtLength) {
		return this.keySuffixLength + this.keyExtLength == keySuffixAndExtLength;
	}

	/**
	 * Keep only suffix and ext
	 */
	protected byte[] stripPrefix(byte[] key) {
		return Arrays.copyOfRange(key, this.keyPrefix.length, key.length);
	}

	/**
	 * Remove ext from suffix
	 */
	protected byte[] trimSuffix(byte[] keySuffix) {
		if (keySuffix.length == keySuffixLength)
			return keySuffix;
		return Arrays.copyOf(keySuffix, keySuffixLength);
	}

	/**
	 * Remove ext from full key
	 */
	protected byte[] removeExtFromFullKey(byte[] key) {
		return Arrays.copyOf(key, keyPrefix.length + keySuffixLength);
	}

	/**
	 * Add prefix to suffix
	 */
	protected byte[] toKeyWithoutExt(byte[] suffixKey) {
		assert suffixKey.length == keySuffixLength;
		byte[] result = Arrays.copyOf(keyPrefix, keyPrefix.length + keySuffixLength);
		System.arraycopy(suffixKey, 0, result, keyPrefix.length, keySuffixLength);
		return result;
	}

	/**
	 * Remove suffix from keySuffix, returning probably an empty byte array
	 */
	protected byte[] stripSuffix(byte[] keySuffix) {
		if (keySuffix.length == this.keySuffixLength)
			return EMPTY_BYTES;
		return Arrays.copyOfRange(keySuffix, this.keySuffixLength, keySuffix.length);
	}

	protected LLSnapshot resolveSnapshot(@Nullable CompositeSnapshot snapshot) {
		if (snapshot == null) {
			return null;
		} else {
			return snapshot.getSnapshot(dictionary);
		}
	}

	protected LLRange toExtRange(byte[] keySuffix) {
		byte[] first = firstKey(keyPrefix, keySuffix, keyPrefix.length, keySuffixLength, keyExtLength);
		byte[] end = lastKey(keyPrefix, keySuffix, keyPrefix.length, keySuffixLength, keyExtLength);
		return LLRange.of(first, end);
	}

	@Override
	public Mono<US> at(@Nullable CompositeSnapshot snapshot, T keySuffix) {
		byte[] keySuffixData = serializeSuffix(keySuffix);
		Flux<byte[]> rangeKeys = this
				.dictionary.getRangeKeys(resolveSnapshot(snapshot), toExtRange(keySuffixData)
		);
		return this.subStageGetter
				.subStage(dictionary, snapshot, toKeyWithoutExt(keySuffixData), rangeKeys);
	}

	@Override
	public Flux<Entry<T, US>> getAllStages(@Nullable CompositeSnapshot snapshot) {
		Flux<GroupedFlux<byte[], byte[]>> groupedFlux = dictionary
				.getRangeKeys(resolveSnapshot(snapshot), range)
				.groupBy(this::removeExtFromFullKey);
		return groupedFlux
				.flatMap(rangeKeys -> this.subStageGetter
						.subStage(dictionary, snapshot, rangeKeys.key(), rangeKeys)
						.map(us -> Map.entry(this.deserializeSuffix(this.stripPrefix(rangeKeys.key())), us))
				);
	}

	@Override
	public Flux<Entry<T, U>> setAllValuesAndGetPrevious(Flux<Entry<T, U>> entries) {
		var newValues = entries
				.flatMap(entry -> at(null, entry.getKey()).map(us -> Tuples.of(us, entry.getValue())))
				.flatMap(tuple -> tuple.getT1().set(tuple.getT2()));

		return getAllStages(null)
				.flatMap(stage -> stage.getValue().get(null).map(val -> Map.entry(stage.getKey(), val)))
				.concatWith(newValues.then(Mono.empty()));
	}

	//todo: temporary wrapper. convert the whole class to buffers
	protected T deserializeSuffix(byte[] keySuffix) {
		var serialized = Unpooled.wrappedBuffer(keySuffix);
		return keySuffixSerializer.deserialize(serialized);
	}

	//todo: temporary wrapper. convert the whole class to buffers
	protected byte[] serializeSuffix(T keySuffix) {
		var output = Unpooled.buffer(keySuffixLength, keySuffixLength);
		var outputBytes = new byte[keySuffixLength];
		keySuffixSerializer.serialize(keySuffix, output);
		output.getBytes(0, outputBytes, 0, keySuffixLength);
		return outputBytes;
	}
}