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Tools for working with logs stored on different partitions.
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/*
 * Copyright (C) 2020 ActiveJ LLC.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package io.activej.multilog;

import io.activej.bytebuf.ByteBuf;
import io.activej.common.time.CurrentTimeProvider;
import io.activej.csp.ChannelInput;
import io.activej.csp.consumer.ChannelConsumer;
import io.activej.csp.process.AbstractCommunicatingProcess;
import io.activej.csp.supplier.ChannelSupplier;
import io.activej.fs.IFileSystem;
import io.activej.promise.Promise;
import org.jetbrains.annotations.Nullable;

import java.util.function.UnaryOperator;

import static io.activej.reactor.Reactive.checkInReactorThread;

public final class LogStreamChunker extends AbstractCommunicatingProcess implements ChannelInput {
	private final CurrentTimeProvider currentTimeProvider;
	private final IFileSystem fileSystem;
	private final LogNamingScheme namingScheme;
	private final String logPartition;
	private final UnaryOperator> consumerTransformer;

	private ChannelSupplier input;
	private @Nullable ChannelConsumer currentConsumer;

	private LogFile currentChunk;

	public LogStreamChunker(CurrentTimeProvider currentTimeProvider, IFileSystem fileSystem, LogNamingScheme namingScheme, String logPartition, UnaryOperator> consumerTransformer) {
		this.currentTimeProvider = currentTimeProvider;
		this.fileSystem = fileSystem;
		this.namingScheme = namingScheme;
		this.logPartition = logPartition;
		this.consumerTransformer = consumerTransformer;
	}

	@Override
	public Promise set(ChannelSupplier input) {
		checkInReactorThread(this);
		this.input = sanitize(input);
		startProcess();
		return getProcessCompletion();
	}

	@Override
	protected void doProcess() {
		input.get()
			.whenResult(buf -> {
				if (buf != null) {
					//noinspection ConstantConditions
					ensureConsumer()
						.then(() -> currentConsumer.accept(buf))
						.whenResult(this::doProcess);
				} else {
					flush().whenResult(this::completeProcess);
				}
			});
	}

	private Promise ensureConsumer() {
		LogFile newChunkName = namingScheme.format(currentTimeProvider.currentTimeMillis());
		return currentChunk != null && currentChunk.getName().compareTo(newChunkName.getName()) >= 0 ?
			Promise.complete() :
			startNewChunk(newChunkName);
	}

	private Promise startNewChunk(LogFile newChunkName) {
		return flush()
			.then(() -> {
				this.currentChunk = (currentChunk == null) ? newChunkName : new LogFile(newChunkName.getName(), 0);
				return fileSystem.append(namingScheme.path(logPartition, currentChunk), 0)
					.then(this::doSanitize)
					.whenResult(newConsumer -> this.currentConsumer = consumerTransformer.apply(sanitize(newConsumer)))
					.toVoid();
			});
	}

	private Promise flush() {
		if (currentConsumer == null) {
			return Promise.complete();
		}
		return currentConsumer.acceptEndOfStream()
			.whenResult(() -> currentConsumer = null);
	}

	@Override
	protected void doClose(Exception e) {
		input.closeEx(e);
		if (currentConsumer != null) {
			currentConsumer.closeEx(e);
		}
	}
}