/*
 * 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 javax.inject.Named;
import javax.inject.Singleton;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.io.UncheckedIOException;
import java.nio.channels.FileChannel;
import java.nio.channels.FileLock;
import java.nio.channels.OverlappingFileLockException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.Map;
import java.util.Properties;

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

/**
 * Manages access to a properties file.
 * <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.
 */
@Singleton
@Named
public final class DefaultTrackingFileManager implements TrackingFileManager {
    private static final Logger LOGGER = LoggerFactory.getLogger(DefaultTrackingFileManager.class);

    @Override
    public Properties read(File file) {
        Path filePath = file.toPath();
        if (Files.isReadable(filePath)) {
            synchronized (getMutex(filePath)) {
                try (FileInputStream stream = new FileInputStream(filePath.toFile());
                        FileLock unused = fileLock(stream.getChannel(), Math.max(1, file.length()), true)) {
                    Properties props = new Properties();
                    props.load(stream);
                    return props;
                } catch (IOException e) {
                    LOGGER.warn("Failed to read tracking file '{}'", file, e);
                    throw new UncheckedIOException(e);
                }
            }
        }
        return null;
    }

    @Override
    public Properties update(File file, Map<String, String> updates) {
        Path filePath = file.toPath();
        Properties props = new Properties();

        try {
            Files.createDirectories(filePath.getParent());
        } catch (IOException e) {
            LOGGER.warn("Failed to create tracking file parent '{}'", file, e);
            throw new UncheckedIOException(e);
        }

        synchronized (getMutex(filePath)) {
            try (RandomAccessFile raf = new RandomAccessFile(filePath.toFile(), "rw");
                    FileLock unused = fileLock(raf.getChannel(), Math.max(1, raf.length()), false)) {
                if (raf.length() > 0) {
                    byte[] buffer = new byte[(int) raf.length()];
                    raf.readFully(buffer);
                    props.load(new ByteArrayInputStream(buffer));
                }

                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 '{}'", file);
                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.");
                raf.seek(0L);
                raf.write(stream.toByteArray());
                raf.setLength(raf.getFilePointer());
            } catch (IOException e) {
                LOGGER.warn("Failed to write tracking file '{}'", file, e);
                throw new UncheckedIOException(e);
            }
        }

        return props;
    }

    private Object getMutex(Path file) {
        /*
         * NOTE: Locks held by one JVM must not overlap and using the canonical path is our best bet, still another
         * piece of code might have locked the same file (unlikely though) or the canonical path fails to capture file
         * identity sufficiently as is the case with Java 1.6 and symlinks on Windows.
         */
        try {
            return file.toRealPath().toString().intern();
        } catch (IOException e) {
            LOGGER.warn("Failed to get real path {}", file, e);
            return file.toAbsolutePath().toString().intern();
        }
    }

    @SuppressWarnings({"checkstyle:magicnumber"})
    private FileLock fileLock(FileChannel channel, long size, boolean shared) throws IOException {
        FileLock lock = null;
        for (int attempts = 8; attempts >= 0; attempts--) {
            try {
                lock = channel.lock(0, size, shared);
                break;
            } catch (OverlappingFileLockException e) {
                if (attempts <= 0) {
                    throw 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;
    }
}
