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/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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 org.eclipse.aether.named.providers;

import javax.inject.Named;
import javax.inject.Singleton;

import java.io.IOException;
import java.io.UncheckedIOException;
import java.nio.channels.FileChannel;
import java.nio.file.AccessDeniedException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;

import org.eclipse.aether.named.support.FileLockNamedLock;
import org.eclipse.aether.named.support.NamedLockFactorySupport;
import org.eclipse.aether.named.support.NamedLockSupport;

import static org.eclipse.aether.named.support.Retry.retry;

/**
 * Named locks factory of {@link FileLockNamedLock}s. This is a bit special implementation, as it
 * expects locks names to be fully qualified absolute file system paths.
 *
 * @since 1.7.3
 */
@Singleton
@Named(FileLockNamedLockFactory.NAME)
public class FileLockNamedLockFactory extends NamedLockFactorySupport {
    public static final String NAME = "file-lock";

    /**
     * Tweak: on Windows, the presence of {@link StandardOpenOption#DELETE_ON_CLOSE} causes concurrency issues. This
     * flag allows to have it removed from effective flags, at the cost that lockfile directory becomes crowded
     * with 0 byte sized lock files that are never cleaned up. Default value is {@code true}.
     *
     * @see JDK-8252883
     */
    private static final boolean DELETE_LOCK_FILES =
            Boolean.parseBoolean(System.getProperty("aether.named.file-lock.deleteLockFiles", Boolean.TRUE.toString()));

    /**
     * Tweak: on Windows, the presence of {@link StandardOpenOption#DELETE_ON_CLOSE} causes concurrency issues. This
     * flag allows to implement similar fix as referenced JDK bug report: retry and hope the best. Default value is
     * 5 attempts (will retry 4 times).
     *
     * @see JDK-8252883
     */
    private static final int ATTEMPTS = Integer.parseInt(System.getProperty("aether.named.file-lock.attempts", "5"));

    /**
     * Tweak: When {@link #ATTEMPTS} used, the amount of milliseconds to sleep between subsequent retries. Default
     * value is 50 milliseconds.
     */
    private static final long SLEEP_MILLIS =
            Long.parseLong(System.getProperty("aether.named.file-lock.sleepMillis", "50"));

    private final ConcurrentMap fileChannels;

    public FileLockNamedLockFactory() {
        this.fileChannels = new ConcurrentHashMap<>();
    }

    @Override
    protected NamedLockSupport createLock(final String name) {
        Path path = Paths.get(name);
        FileChannel fileChannel = fileChannels.computeIfAbsent(name, k -> {
            try {
                Files.createDirectories(path.getParent());
                FileChannel channel = retry(
                        ATTEMPTS,
                        SLEEP_MILLIS,
                        () -> {
                            try {
                                if (DELETE_LOCK_FILES) {
                                    return FileChannel.open(
                                            path,
                                            StandardOpenOption.READ,
                                            StandardOpenOption.WRITE,
                                            StandardOpenOption.CREATE,
                                            StandardOpenOption.DELETE_ON_CLOSE);
                                } else {
                                    return FileChannel.open(
                                            path,
                                            StandardOpenOption.READ,
                                            StandardOpenOption.WRITE,
                                            StandardOpenOption.CREATE);
                                }
                            } catch (AccessDeniedException e) {
                                return null;
                            }
                        },
                        null,
                        null);

                if (channel == null) {
                    throw new IllegalStateException("Could not open file channel for '" + name + "' after " + ATTEMPTS
                            + " attempts; giving up");
                }
                return channel;
            } catch (InterruptedException e) {
                Thread.currentThread().interrupt();
                throw new RuntimeException("Interrupted while opening file channel for '" + name + "'", e);
            } catch (IOException e) {
                throw new UncheckedIOException("Failed to open file channel for '" + name + "'", e);
            }
        });
        return new FileLockNamedLock(name, fileChannel, this);
    }

    @Override
    protected void destroyLock(final String name) {
        FileChannel fileChannel = fileChannels.remove(name);
        if (fileChannel == null) {
            throw new IllegalStateException("File channel expected, but does not exist: " + name);
        }

        try {
            fileChannel.close();
        } catch (IOException e) {
            throw new UncheckedIOException("Failed to close file channel for '" + name + "'", e);
        }
    }
}