/*
 *  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.tools.ant.types.selectors.modifiedselector;

import java.io.BufferedInputStream;
import java.io.File;
import java.nio.file.Files;
import java.security.NoSuchAlgorithmException;
import java.util.Locale;
import java.util.zip.Adler32;
import java.util.zip.CRC32;
import java.util.zip.CheckedInputStream;
import java.util.zip.Checksum;

import org.apache.tools.ant.BuildException;


/**
 * Computes a 'checksum' for the content of file using
 * java.util.zip.CRC32 and java.util.zip.Adler32.
 * Use of this algorithm doesn't require any additional nested &lt;param&gt;s.
 * Supported &lt;param&gt;s are:
 * <table>
 * <caption>Checksum algorithm parameters</caption>
 * <tr>
 *   <th>name</th><th>values</th><th>description</th><th>required</th>
 * </tr>
 * <tr>
 *   <td>algorithm.algorithm</td>
 *   <td>ADLER | CRC (default)</td>
 *   <td>name of the algorithm the checksum should use</td>
 *   <td>no, defaults to CRC</td>
 * </tr>
 * </table>
 *
 * @version 2004-06-17
 * @since  Ant 1.7
 */
public class ChecksumAlgorithm implements Algorithm {


    // -----  member variables  -----


    /**
     * Checksum algorithm to be used.
     */
    private String algorithm = "CRC";

    /**
     * Checksum interface instance
     */
    private Checksum checksum = null;


    // -----  Algorithm-Configuration  -----


    /**
     * Specifies the algorithm to be used to compute the checksum.
     * Defaults to "CRC". Other popular algorithms like "ADLER" may be used as well.
     * @param algorithm the digest algorithm to use
     */
    public void setAlgorithm(String algorithm) {
        this.algorithm =
            algorithm != null ? algorithm.toUpperCase(Locale.ENGLISH) : null;
    }


    /** Initialize the checksum interface. */
    public void initChecksum() {
        if (checksum != null) {
            return;
        }
        if ("CRC".equals(algorithm)) {
            checksum = new CRC32();
        } else if ("ADLER".equals(algorithm)) {
            checksum = new Adler32();
        } else {
            throw new BuildException(new NoSuchAlgorithmException());
        }
    }


    // -----  Logic  -----


    /**
     * This algorithm supports only CRC and Adler.
     * @return <i>true</i> if all is ok, otherwise <i>false</i>.
     */
    @Override
    public boolean isValid() {
        return "CRC".equals(algorithm) || "ADLER".equals(algorithm);
    }


    /**
     * Computes a value for a file content with the specified checksum algorithm.
     * @param file    File object for which the value should be evaluated.
     * @return        The value for that file
     */
    @Override
    public String getValue(File file) {
        initChecksum();

        if (file.canRead()) {
            checksum.reset();
            try (CheckedInputStream check = new CheckedInputStream(
                new BufferedInputStream(Files.newInputStream(file.toPath())), checksum)) {
                // Read the file
                while (check.read() != -1) {
                }
                return Long.toString(check.getChecksum().getValue());
            } catch (Exception ignored) {
            }
        }
        return null;
    }


    /**
     * Override Object.toString().
     * @return some information about this algorithm.
     */
    @Override
    public String toString() {
        return String.format("<ChecksumAlgorithm:algorithm=%s>", algorithm);
    }
}
