/*
    * 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.util;
  
  import java.io.BufferedReader;
  import java.io.ByteArrayInputStream;
  import java.io.File;
  import java.io.FileInputStream;
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.InputStreamReader;
  import java.nio.charset.StandardCharsets;
  import java.security.MessageDigest;
  import java.security.NoSuchAlgorithmException;
  import java.util.Collection;
  import java.util.LinkedHashMap;
  import java.util.Map;
  
  /**
   * A utility class to assist in the verification and generation of checksums.
   */
  public final class ChecksumUtils {
  
      private ChecksumUtils() {
          // hide constructor
      }
  
      /**
       * Extracts the checksum from the specified file.
       *
       * @param checksumFile The path to the checksum file, must not be {@code null}.
       * @return The checksum stored in the file, never {@code null}.
       * @throws IOException If the checksum does not exist or could not be read for other reasons.
       * @deprecated Use SPI FileProcessor to read and write checksum files.
       */
      @Deprecated
      public static String read(File checksumFile) throws IOException {
          String checksum = "";
          try (BufferedReader br = new BufferedReader(
                  new InputStreamReader(new FileInputStream(checksumFile), StandardCharsets.UTF_8), 512)) {
              while (true) {
                  String line = br.readLine();
                  if (line == null) {
                      break;
                  }
                  line = line.trim();
                  if (line.length() > 0) {
                      checksum = line;
                      break;
                  }
              }
          }
  
          if (checksum.matches(".+= [0-9A-Fa-f]+")) {
              int lastSpacePos = checksum.lastIndexOf(' ');
              checksum = checksum.substring(lastSpacePos + 1);
          } else {
              int spacePos = checksum.indexOf(' ');
  
              if (spacePos != -1) {
                  checksum = checksum.substring(0, spacePos);
              }
          }
  
          return checksum;
      }
  
      /**
       * Calculates checksums for the specified file.
       *
       * @param dataFile The file for which to calculate checksums, must not be {@code null}.
       * @param algos The names of checksum algorithms (cf. {@link MessageDigest#getInstance(String)} to use, must not be
       *            {@code null}.
       * @return The calculated checksums, indexed by algorithm name, or the exception that occurred while trying to
       *         calculate it, never {@code null}.
       * @throws IOException If the data file could not be read.
       * @deprecated Use SPI checksum selector instead.
       */
      @Deprecated
      public static Map<String, Object> calc(File dataFile, Collection<String> algos) throws IOException {
          return calc(new FileInputStream(dataFile), algos);
      }
  
     /**
      * @deprecated Use SPI checksum selector instead.
      */
     @Deprecated
     public static Map<String, Object> calc(byte[] dataBytes, Collection<String> algos) throws IOException {
         return calc(new ByteArrayInputStream(dataBytes), algos);
     }
 
     private static Map<String, Object> calc(InputStream data, Collection<String> algos) throws IOException {
         Map<String, Object> results = new LinkedHashMap<>();
 
         Map<String, MessageDigest> digests = new LinkedHashMap<>();
         for (String algo : algos) {
             try {
                 digests.put(algo, MessageDigest.getInstance(algo));
             } catch (NoSuchAlgorithmException e) {
                 results.put(algo, e);
             }
         }
 
         try (InputStream in = data) {
             for (byte[] buffer = new byte[32 * 1024]; ; ) {
                 int read = in.read(buffer);
                 if (read < 0) {
                     break;
                 }
                 for (MessageDigest digest : digests.values()) {
                     digest.update(buffer, 0, read);
                 }
             }
         }
 
         for (Map.Entry<String, MessageDigest> entry : digests.entrySet()) {
             byte[] bytes = entry.getValue().digest();
 
             results.put(entry.getKey(), toHexString(bytes));
         }
 
         return results;
     }
 
     /**
      * Creates a hexadecimal representation of the specified bytes. Each byte is converted into a two-digit hex number
      * and appended to the result with no separator between consecutive bytes.
      *
      * @param bytes The bytes to represent in hex notation, may be be {@code null}.
      * @return The hexadecimal representation of the input or {@code null} if the input was {@code null}.
      */
     @SuppressWarnings("checkstyle:magicnumber")
     public static String toHexString(byte[] bytes) {
         if (bytes == null) {
             return null;
         }
 
         StringBuilder buffer = new StringBuilder(bytes.length * 2);
 
         for (byte aByte : bytes) {
             int b = aByte & 0xFF;
             if (b < 0x10) {
                 buffer.append('0');
             }
             buffer.append(Integer.toHexString(b));
         }
 
         return buffer.toString();
     }
 
     /**
      * Creates a byte array out of hexadecimal representation of the specified bytes. If input string is {@code null},
      * {@code null} is returned. Input value must have even length (due hex encoding = 2 chars one byte).
      *
      * @param hexString The hexString to convert to byte array, may be {@code null}.
      * @return The byte array of the input or {@code null} if the input was {@code null}.
      * @since 1.8.0
      */
     @SuppressWarnings("checkstyle:magicnumber")
     public static byte[] fromHexString(String hexString) {
         if (hexString == null) {
             return null;
         }
         if (hexString.isEmpty()) {
             return new byte[] {};
         }
         int len = hexString.length();
         if (len % 2 != 0) {
             throw new IllegalArgumentException("hexString length not even");
         }
         byte[] data = new byte[len / 2];
         for (int i = 0; i < len; i += 2) {
             data[i / 2] = (byte)
                     ((Character.digit(hexString.charAt(i), 16) << 4) + Character.digit(hexString.charAt(i + 1), 16));
         }
         return data;
     }
 }