/*
    * Licensed to The Apereo Foundation under one or more contributor license
    * agreements. See the NOTICE file distributed with this work for additional
    * information regarding copyright ownership.
    *
    *
    * The Apereo Foundation licenses this file to you under the Educational
    * Community 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://opensource.org/licenses/ecl2.txt
   *
   * 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.opencastproject.kernel.security;
  
  import org.apache.commons.io.IOUtils;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  import org.springframework.security.crypto.codec.Hex;
  
  import java.io.File;
  import java.io.FileInputStream;
  import java.io.IOException;
  import java.net.InetAddress;
  import java.net.UnknownHostException;
  import java.nio.charset.StandardCharsets;
  import java.security.MessageDigest;
  import java.security.NoSuchAlgorithmException;
  import java.util.Arrays;
  import java.util.Objects;
  
  /**
   *
   */
  public final class SystemTokenRememberMeUtils {
  
    private static final Logger logger = LoggerFactory.getLogger(SystemTokenRememberMeUtils.class);
  
    /** This is the default cookie key, that is configured in Opencast **/
    private static final String DEFAULT_COOKIE_KEY = "opencast";
  
    private SystemTokenRememberMeUtils() {
    }
  
    public static String augmentKey(String key) {
  
      if (!DEFAULT_COOKIE_KEY.equals(key)) {
        logger.debug("The default cookie key '{}' is not in use. The given key won't be augmented.", DEFAULT_COOKIE_KEY);
        return key;
      }
  
      // Start with a user key if provided
      StringBuilder keyBuilder = new StringBuilder(Objects.toString(key, ""));
  
      // This will give us the hostname and IP address as something which should be unique per system.
      // For example: lk.elan-ev.de/10.10.10.31
      try {
        keyBuilder.append(InetAddress.getLocalHost());
      } catch (UnknownHostException e) {
        // silently ignore this
      }
  
      // Gather additional system properties as key
      // This requires a proc-fs which should generally be available under Linux.
      // But even without, we have fallbacks above and below.
      for (String procFile: Arrays.asList("/proc/version", "/proc/partitions")) {
        try (FileInputStream fileInputStream = new FileInputStream(new File(procFile))) {
          keyBuilder.append(IOUtils.toString(fileInputStream, StandardCharsets.UTF_8));
        } catch (IOException e) {
          // ignore this
        }
      }
  
      // If we still have no proper key, just generate a random one.
      // This will work just fine with the single drawback that restarting Opencast invalidates all remember-me tokens.
      // But it should be a sufficiently good fallback.
      key = keyBuilder.toString();
      if (key.isEmpty()) {
        logger.warn("Could not generate semi-persistent remember-me key. Will generate a non-persistent random one.");
        key = Double.toString(Math.random());
      }
      logger.debug("Remember me key before hashing: {}", key);
  
      // Use a SHA-512 hash as key to have a more sane key.
      try {
        MessageDigest digest = MessageDigest.getInstance("SHA-512");
        key = new String(Hex.encode(digest.digest(key.getBytes())));
      } catch (NoSuchAlgorithmException e) {
        logger.warn("No SHA-512 algorithm available!");
      }
      logger.debug("Calculated remember me key: {}", key);
     return key;
   }
 }