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Apache Commons Compress defines an API for working with compression and archive formats. These include bzip2, gzip, pack200, LZMA, XZ, Snappy, traditional Unix Compress, DEFLATE, DEFLATE64, LZ4, Brotli, Zstandard and ar, cpio, jar, tar, zip, dump, 7z, arj.
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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.apache.commons.compress.archivers.ar;

import java.io.File;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.LinkOption;
import java.nio.file.Path;
import java.util.Date;
import java.util.Objects;

import org.apache.commons.compress.archivers.ArchiveEntry;

/**
 * Represents an archive entry in the "ar" format.
 * 
 * Each AR archive starts with "!<arch>" followed by a LF. After these 8 bytes the archive entries are listed. The format of an entry header is as it
 * follows:
 * 
 *
 *  * START BYTE   END BYTE    NAME                    FORMAT      LENGTH
 * 0            15          File name               ASCII       16
 * 16           27          Modification timestamp  Decimal     12
 * 28           33          Owner ID                Decimal     6
 * 34           39          Group ID                Decimal     6
 * 40           47          File mode               Octal       8
 * 48           57          File size (bytes)       Decimal     10
 * 58           59          File magic              \140\012    2
 * 
 * 
 * This specifies that an ar archive entry header contains 60 bytes.
 * 
 * 
 * Due to the limitation of the file name length to 16 bytes GNU and BSD has their own variants of this format. Currently Commons Compress can read but not
 * write the GNU variant. It fully supports the BSD variant.
 * 
 *
 * @see ar man page
 * @Immutable
 */
public class ArArchiveEntry implements ArchiveEntry {

    /** The header for each entry */
    public static final String HEADER = "!\n";

    /** The trailer for each entry */
    public static final String TRAILER = "`\012";

    private static final int DEFAULT_MODE = 33188; // = (octal) 0100644

    /**
     * SVR4/GNU adds a trailing / to names; BSD does not. They also vary in how names longer than 16 characters are represented. (Not yet fully supported by
     * this implementation)
     */
    private final String name;
    private final int userId;
    private final int groupId;
    private final int mode;
    private final long lastModified;
    private final long length;

    /**
     * Creates a new instance using the attributes of the given file
     *
     * @param inputFile the file to create an entry from
     * @param entryName the name of the entry
     */
    public ArArchiveEntry(final File inputFile, final String entryName) {
        // TODO sort out mode
        this(entryName, inputFile.isFile() ? inputFile.length() : 0, 0, 0, DEFAULT_MODE, inputFile.lastModified() / 1000);
    }

    /**
     * Creates a new instance using the attributes of the given file
     *
     * @param inputPath the file to create an entry from
     * @param entryName the name of the entry
     * @param options   options indicating how symbolic links are handled.
     * @throws IOException if an I/O error occurs.
     * @since 1.21
     */
    public ArArchiveEntry(final Path inputPath, final String entryName, final LinkOption... options) throws IOException {
        this(entryName, Files.isRegularFile(inputPath, options) ? Files.size(inputPath) : 0, 0, 0, DEFAULT_MODE,
                Files.getLastModifiedTime(inputPath, options).toMillis() / 1000);
    }

    /**
     * Constructs a new instance using a couple of default values.
     *
     * 
     * Sets userId and groupId to 0, the octal file mode to 644 and the last modified time to the current time.
     * 
     *
     * @param name   name of the entry
     * @param length length of the entry in bytes
     */
    public ArArchiveEntry(final String name, final long length) {
        this(name, length, 0, 0, DEFAULT_MODE, System.currentTimeMillis() / 1000);
    }

    /**
     * Constructs a new instance.
     *
     * @param name         name of the entry
     * @param length       length of the entry in bytes
     * @param userId       numeric user id
     * @param groupId      numeric group id
     * @param mode         file mode
     * @param lastModified last modified time in seconds since the epoch
     */
    public ArArchiveEntry(final String name, final long length, final int userId, final int groupId, final int mode, final long lastModified) {
        this.name = name;
        if (length < 0) {
            throw new IllegalArgumentException("length must not be negative");
        }
        this.length = length;
        this.userId = userId;
        this.groupId = groupId;
        this.mode = mode;
        this.lastModified = lastModified;
    }

    @Override
    public boolean equals(final Object obj) {
        if (this == obj) {
            return true;
        }
        if (obj == null || getClass() != obj.getClass()) {
            return false;
        }
        final ArArchiveEntry other = (ArArchiveEntry) obj;
        if (name == null) {
            return other.name == null;
        }
        return name.equals(other.name);
    }

    /**
     * Gets the group ID.
     *
     * @return the group ID.
     */
    public int getGroupId() {
        return groupId;
    }

    /**
     * Gets the last modified time in seconds since the epoch.
     *
     * @return the last modified date.
     */
    public long getLastModified() {
        return lastModified;
    }

    @Override
    public Date getLastModifiedDate() {
        return new Date(1000 * getLastModified());
    }

    /**
     * Gets the length.
     *
     * @return the length.
     */
    public long getLength() {
        return length;
    }

    /**
     * Gets the mode.
     *
     * @return the mode.
     */
    public int getMode() {
        return mode;
    }

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

    @Override
    public long getSize() {
        return this.getLength();
    }

    /**
     * Gets the user ID.
     *
     * @return the user ID.
     */
    public int getUserId() {
        return userId;
    }

    @Override
    public int hashCode() {
        return Objects.hash(name);
    }

    @Override
    public boolean isDirectory() {
        return false;
    }
}