/*
 * 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.internal.impl;

import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.IOException;
import java.io.UncheckedIOException;
import java.nio.ByteBuffer;
import java.nio.channels.Channels;
import java.nio.channels.FileChannel;
import java.nio.channels.FileLock;
import java.nio.channels.OverlappingFileLockException;
import java.nio.file.Files;
import java.nio.file.NoSuchFileException;
import java.nio.file.Path;
import java.nio.file.StandardOpenOption;
import java.util.Map;
import java.util.Properties;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Manages access to a properties file in legacy compatible way.
 * <p>
 * Note: the file locking in this component (that predates {@link org.eclipse.aether.SyncContext}) is present only
 * to back off two parallel implementations that coexist in Maven (this class and {@code maven-compat} one), as in
 * certain cases the two implementations may collide on properties files. This locking must remain in place for as long
 * as {@code maven-compat} code exists.
 * <p>
 * This implementation should be used when multiple, legacy Maven versions (older than 3.10.x) share same local repository
 * concurrently.
 *
 * @since 2.0.17
 * @see NamedLocksTrackingFileManager
 * @see TrackingFileManagerProvider
 */
public final class LegacyTrackingFileManager implements TrackingFileManager {
    private static final Logger LOGGER = LoggerFactory.getLogger(LegacyTrackingFileManager.class);

    @Deprecated
    @Override
    public Properties read(File file) {
        return read(file.toPath());
    }

    @Override
    public Properties read(Path path) {
        if (Files.isReadable(path)) {
            synchronized (mutex(path)) {
                try (FileChannel fileChannel = FileChannel.open(path, StandardOpenOption.READ);
                        FileLock unused = fileLock(fileChannel, true)) {
                    Properties props = new Properties();
                    props.load(Channels.newInputStream(fileChannel));
                    return props;
                } catch (NoSuchFileException e) {
                    LOGGER.debug("No such file to read {}: {}", path, e.getMessage());
                } catch (IOException e) {
                    LOGGER.warn("Failed to read tracking file '{}'", path, e);
                    throw new UncheckedIOException(e);
                }
            }
        }
        return null;
    }

    @Deprecated
    @Override
    public Properties update(File file, Map<String, String> updates) {
        return update(file.toPath(), updates);
    }

    @Override
    public Properties update(Path path, Map<String, String> updates) {
        try {
            Files.createDirectories(path.getParent());
        } catch (IOException e) {
            LOGGER.warn("Failed to create tracking file parent '{}'", path, e);
            throw new UncheckedIOException(e);
        }
        synchronized (mutex(path)) {
            try (FileChannel fileChannel = FileChannel.open(
                            path, StandardOpenOption.READ, StandardOpenOption.WRITE, StandardOpenOption.CREATE);
                    FileLock unused = fileLock(fileChannel, false)) {
                Properties props = new Properties();
                if (fileChannel.size() > 0) {
                    props.load(Channels.newInputStream(fileChannel));
                }

                for (Map.Entry<String, String> update : updates.entrySet()) {
                    if (update.getValue() == null) {
                        props.remove(update.getKey());
                    } else {
                        props.setProperty(update.getKey(), update.getValue());
                    }
                }

                LOGGER.debug("Writing tracking file '{}'", path);
                ByteArrayOutputStream stream = new ByteArrayOutputStream(1024 * 2);
                props.store(
                        stream,
                        "NOTE: This is a Maven Resolver internal implementation file"
                                + ", its format can be changed without prior notice.");
                fileChannel.position(0);
                int written = fileChannel.write(ByteBuffer.wrap(stream.toByteArray()));
                fileChannel.truncate(written);
                return props;
            } catch (IOException e) {
                LOGGER.warn("Failed to write tracking file '{}'", path, e);
                throw new UncheckedIOException(e);
            }
        }
    }

    @Deprecated
    @Override
    public boolean delete(File file) {
        return delete(file.toPath());
    }

    @Override
    public boolean delete(Path path) {
        if (Files.isReadable(path)) {
            synchronized (mutex(path)) {
                try (FileChannel fileChannel = FileChannel.open(path, StandardOpenOption.WRITE);
                        FileLock unused = fileLock(fileChannel, false)) {
                    Files.delete(path);
                    return true;
                } catch (NoSuchFileException e) {
                    LOGGER.debug("No such file to delete {}: {}", path, e.getMessage());
                } catch (IOException e) {
                    LOGGER.warn("Failed to delete tracking file '{}'", path, e);
                    throw new UncheckedIOException(e);
                }
            }
        }
        return false;
    }

    /**
     * This method creates a "mutex" object to synchronize on thread level, within same JVM, to prevent multiple
     * threads from trying to lock the same file at the same time. Threads concurrently working on different files
     * are okay, as after syncing on mutex, they operate with FS locking, that goal is to synchronize with possible
     * other Maven processes, and not with other threads in this JVM.
     */
    private static Object mutex(Path path) {
        // The interned string of path is (mis)used as mutex, to exclude different threads going for same file,
        // as JVM file locking happens on JVM not on Thread level. This is how original code did it  ¯\_(ツ)_/¯
        return canonicalPath(path).toString().intern();
    }

    /**
     * Tries the best it can to figure out actual file the workload is about, while resolving cases like symlinked
     * local repository etc.
     */
    private static Path canonicalPath(Path path) {
        try {
            return path.toRealPath();
        } catch (IOException e) {
            return canonicalPath(path.getParent()).resolve(path.getFileName());
        }
    }

    private FileLock fileLock(FileChannel channel, boolean shared) throws IOException {
        FileLock lock = null;
        for (int attempts = 8; attempts >= 0; attempts--) {
            try {
                lock = channel.lock(0, Long.MAX_VALUE, shared);
                break;
            } catch (OverlappingFileLockException | IOException e) {
                // For Unix process sun.nio.ch.UnixFileDispatcherImpl.lock0() is a native method that can throw
                // IOException with message "Resource deadlock avoided"
                // the system call level is involving fcntl() or flock()
                // If the kernel detects that granting the lock would result in a deadlock
                // (where two processes are waiting for each other to release locks which can happen when two processes
                // are trying to lock the same file),
                // it returns an EDEADLK error, which Java throws as an IOException.
                // Read another comment from
                // https://github.com/bdeployteam/bdeploy/blob/7c04e7228d6d48b8990e6703a8d476e21024c639/bhive/src/main/java/io/bdeploy/bhive/objects/LockableDatabase.java#L57
                // Note (cstamas): seems this MAY also happen where there is ONE process but performs locking on same
                // file from multiple threads, as Linux kernel performs lock detection on process level.
                if (attempts <= 0) {
                    throw (e instanceof IOException) ? (IOException) e : new IOException(e);
                }
                try {
                    Thread.sleep(50L);
                } catch (InterruptedException e1) {
                    Thread.currentThread().interrupt();
                }
            }
        }
        if (lock == null) {
            throw new IOException("Could not lock file");
        }
        return lock;
    }
}
