CavalliumDBEngine/src/main/java/it/cavallium/dbengine/database/disk/LLLocalSingleton.java

package it.cavallium.dbengine.database.disk;

import io.netty5.buffer.api.Buffer;
import io.netty5.buffer.api.BufferAllocator;
import io.netty5.buffer.api.Send;
import it.cavallium.dbengine.database.LLDelta;
import it.cavallium.dbengine.database.LLSingleton;
import it.cavallium.dbengine.database.LLSnapshot;
import it.cavallium.dbengine.database.UpdateReturnMode;
import it.cavallium.dbengine.database.serialization.SerializationFunction;
import java.io.IOException;
import java.util.Arrays;
import java.util.concurrent.Callable;
import java.util.function.Function;
import org.jetbrains.annotations.NotNull;
import org.jetbrains.annotations.Nullable;
import org.rocksdb.ReadOptions;
import org.rocksdb.RocksDBException;
import org.rocksdb.Snapshot;
import org.rocksdb.WriteOptions;
import reactor.core.publisher.Mono;
import reactor.core.scheduler.Scheduler;
import reactor.core.scheduler.Schedulers;

public class LLLocalSingleton implements LLSingleton {

	static final ReadOptions EMPTY_READ_OPTIONS = new UnreleasableReadOptions(new UnmodifiableReadOptions());
	static final WriteOptions EMPTY_WRITE_OPTIONS = new UnreleasableWriteOptions(new UnmodifiableWriteOptions());
	private final RocksDBColumn db;
	private final Function<LLSnapshot, Snapshot> snapshotResolver;
	private final byte[] name;
	private final String columnName;
	private final Mono<Send<Buffer>> nameMono;
	private final String databaseName;
	private final Scheduler dbScheduler;

	public LLLocalSingleton(RocksDBColumn db,
			Function<LLSnapshot, Snapshot> snapshotResolver,
			String databaseName,
			byte[] name,
			String columnName,
			Scheduler dbScheduler,
			byte @Nullable [] defaultValue) throws RocksDBException {
		this.db = db;
		this.databaseName = databaseName;
		this.snapshotResolver = snapshotResolver;
		this.name = name;
		this.columnName = columnName;
		this.nameMono = Mono.fromCallable(() -> {
			var alloc = db.getAllocator();
			try (var nameBuf = alloc.allocate(this.name.length)) {
				nameBuf.writeBytes(this.name);
				return nameBuf.send();
			}
		});
		this.dbScheduler = dbScheduler;
		if (Schedulers.isInNonBlockingThread()) {
			throw new UnsupportedOperationException("Initialized in a nonblocking thread");
		}
		if (defaultValue != null && db.get(EMPTY_READ_OPTIONS, this.name, true) == null) {
			db.put(EMPTY_WRITE_OPTIONS, this.name, defaultValue);
		}
	}

	private <T> @NotNull Mono<T> runOnDb(Callable<@Nullable T> callable) {
		return Mono.fromCallable(callable).subscribeOn(dbScheduler);
	}

	private ReadOptions resolveSnapshot(LLSnapshot snapshot) {
		if (snapshot != null) {
			return new ReadOptions().setSnapshot(snapshotResolver.apply(snapshot));
		} else {
			return EMPTY_READ_OPTIONS;
		}
	}

	@Override
	public BufferAllocator getAllocator() {
		return db.getAllocator();
	}

	@Override
	public Mono<Send<Buffer>> get(@Nullable LLSnapshot snapshot) {
		return nameMono.publishOn(Schedulers.boundedElastic()).handle((nameSend, sink) -> {
			try (Buffer name = nameSend.receive()) {
				Buffer result = db.get(resolveSnapshot(snapshot), name);
				if (result != null) {
					sink.next(result.send());
				} else {
					sink.complete();
				}
			} catch (RocksDBException ex) {
				sink.error(new IOException("Failed to read " + Arrays.toString(name), ex));
			}
		});
	}

	@Override
	public Mono<Void> set(Mono<Send<Buffer>> valueMono) {
		return Mono.zip(nameMono, valueMono).publishOn(Schedulers.boundedElastic()).handle((tuple, sink) -> {
			var nameSend = tuple.getT1();
			var valueSend = tuple.getT2();
			try (Buffer name = nameSend.receive()) {
				try (Buffer value = valueSend.receive()) {
					db.put(EMPTY_WRITE_OPTIONS, name, value);
					sink.next(true);
				}
			} catch (RocksDBException ex) {
				sink.error(new IOException("Failed to write " + Arrays.toString(name), ex));
			}
		}).switchIfEmpty(unset().thenReturn(true)).then();
	}

	private Mono<Void> unset() {
		return nameMono.publishOn(Schedulers.boundedElastic()).handle((nameSend, sink) -> {
			try (Buffer name = nameSend.receive()) {
				db.delete(EMPTY_WRITE_OPTIONS, name);
			} catch (RocksDBException ex) {
				sink.error(new IOException("Failed to read " + Arrays.toString(name), ex));
			}
		});
	}

	@Override
	public Mono<Send<Buffer>> update(SerializationFunction<@Nullable Send<Buffer>, @Nullable Buffer> updater,
			UpdateReturnMode updateReturnMode) {
		return Mono.usingWhen(nameMono, keySend -> runOnDb(() -> {
					if (Schedulers.isInNonBlockingThread()) {
						throw new UnsupportedOperationException("Called update in a nonblocking thread");
					}
					UpdateAtomicResultMode returnMode = switch (updateReturnMode) {
						case NOTHING -> UpdateAtomicResultMode.NOTHING;
						case GET_NEW_VALUE -> UpdateAtomicResultMode.CURRENT;
						case GET_OLD_VALUE -> UpdateAtomicResultMode.PREVIOUS;
					};
					UpdateAtomicResult result
							= db.updateAtomic(EMPTY_READ_OPTIONS, EMPTY_WRITE_OPTIONS, keySend, updater, returnMode);
					return switch (updateReturnMode) {
						case NOTHING -> null;
						case GET_NEW_VALUE -> ((UpdateAtomicResultCurrent) result).current();
						case GET_OLD_VALUE -> ((UpdateAtomicResultPrevious) result).previous();
					};
				}).onErrorMap(cause -> new IOException("Failed to read or write", cause)),
				keySend -> Mono.fromRunnable(keySend::close));
	}

	@Override
	public Mono<Send<LLDelta>> updateAndGetDelta(SerializationFunction<@Nullable Send<Buffer>, @Nullable Buffer> updater) {
		return Mono.usingWhen(nameMono, keySend -> runOnDb(() -> {
					if (Schedulers.isInNonBlockingThread()) {
						throw new UnsupportedOperationException("Called update in a nonblocking thread");
					}
					UpdateAtomicResult result
							= db.updateAtomic(EMPTY_READ_OPTIONS, EMPTY_WRITE_OPTIONS, keySend, updater, UpdateAtomicResultMode.DELTA);
					return ((UpdateAtomicResultDelta) result).delta();
				}).onErrorMap(cause -> new IOException("Failed to read or write", cause)),
				keySend -> Mono.fromRunnable(keySend::close));
	}

	@Override
	public String getDatabaseName() {
		return databaseName;
	}

	@Override
	public String getColumnName() {
		return columnName;
	}

	@Override
	public String getName() {
		return new String(name);
	}
}