/**
 * 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.nutch.protocol;

// JDK imports
import java.io.File;
import java.io.FileReader;
import java.io.LineNumberReader;
import java.net.URL;
import java.util.Hashtable;
import java.util.StringTokenizer;

// Commons Logging imports
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

// Nutch imports
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.conf.Configurable;
import com.google.common.io.Files;

import crawlercommons.robots.BaseRobotRules;
import crawlercommons.robots.SimpleRobotRules;
import crawlercommons.robots.SimpleRobotRules.RobotRulesMode;
import crawlercommons.robots.SimpleRobotRulesParser;

/**
 * This class uses crawler-commons for handling the parsing of
 * {@code robots.txt} files. It emits SimpleRobotRules objects, which describe
 * the download permissions as described in SimpleRobotRulesParser.
 */
public abstract class RobotRulesParser implements Configurable {

  public static final Logger LOG = LoggerFactory
      .getLogger(RobotRulesParser.class);

  protected static final Hashtable<String, BaseRobotRules> CACHE = new Hashtable<String, BaseRobotRules>();

  /**
   * A {@link BaseRobotRules} object appropriate for use when the
   * {@code robots.txt} file is empty or missing; all requests are allowed.
   */
  public static final BaseRobotRules EMPTY_RULES = new SimpleRobotRules(
      RobotRulesMode.ALLOW_ALL);

  /**
   * A {@link BaseRobotRules} object appropriate for use when the
   * {@code robots.txt} file is not fetched due to a {@code 403/Forbidden}
   * response; all requests are disallowed.
   */
  public static BaseRobotRules FORBID_ALL_RULES = new SimpleRobotRules(
      RobotRulesMode.ALLOW_NONE);

  private static SimpleRobotRulesParser robotParser = new SimpleRobotRulesParser();
  private Configuration conf;
  protected String agentNames;

  public RobotRulesParser() {
  }

  public RobotRulesParser(Configuration conf) {
    setConf(conf);
  }

  /**
   * Set the {@link Configuration} object
   */
  public void setConf(Configuration conf) {
    this.conf = conf;

    // Grab the agent names we advertise to robots files.
    String agentName = conf.get("http.agent.name");
    if (agentName == null || (agentName = agentName.trim()).isEmpty()) {
      throw new RuntimeException("Agent name not configured!");
    }
    agentNames = agentName;

    // If there are any other agents specified, append those to the list of
    // agents
    String otherAgents = conf.get("http.robots.agents");
    if (otherAgents != null && !otherAgents.trim().isEmpty()) {
      StringTokenizer tok = new StringTokenizer(otherAgents, ",");
      StringBuilder sb = new StringBuilder(agentNames);
      while (tok.hasMoreTokens()) {
        String str = tok.nextToken().trim();
        if (str.equals("*") || str.equals(agentName)) {
          // skip wildcard "*" or agent name itself
          // (required for backward compatibility, cf. NUTCH-1715 and
          // NUTCH-1718)
        } else {
          sb.append(",").append(str);
        }
      }

      agentNames = sb.toString();
    }
  }

  /**
   * Get the {@link Configuration} object
   */
  public Configuration getConf() {
    return conf;
  }

  /**
   * Parses the robots content using the {@link SimpleRobotRulesParser} from
   * crawler commons
   * 
   * @param url
   *          A string containing url
   * @param content
   *          Contents of the robots file in a byte array
   * @param contentType
   *          The content type of the robots file
   * @param robotName
   *          A string containing all the robots agent names used by parser for
   *          matching
   * @return BaseRobotRules object
   */
  public BaseRobotRules parseRules(String url, byte[] content,
      String contentType, String robotName) {
    return robotParser.parseContent(url, content, contentType, robotName);
  }

  public BaseRobotRules getRobotRulesSet(Protocol protocol, String url) {
    URL u = null;
    try {
      u = new URL(url);
    } catch (Exception e) {
      return EMPTY_RULES;
    }
    return getRobotRulesSet(protocol, u);
  }

  public abstract BaseRobotRules getRobotRulesSet(Protocol protocol, URL url);

  /** command-line main for testing */
  public static void main(String[] argv) {

    if (argv.length != 3) {
      System.err
          .println("Usage: RobotRulesParser <robots-file> <url-file> <agent-names>\n");
      System.err
          .println("    <robots-file> - Input robots.txt file which will be parsed.");
      System.err
          .println("    <url-file>    - Contains input URLs (1 per line) which are tested against the rules.");
      System.err
          .println("    <agent-names> - Input agent names. Multiple agent names can be provided using");
      System.err
          .println("                    comma as a delimiter without any spaces.");
      System.exit(-1);
    }

    try {
      byte[] robotsBytes = Files.toByteArray(new File(argv[0]));
      BaseRobotRules rules = robotParser.parseContent(argv[0], robotsBytes,
          "text/plain", argv[2]);

      LineNumberReader testsIn = new LineNumberReader(new FileReader(argv[1]));
      String testPath = testsIn.readLine().trim();
      while (testPath != null) {
        System.out.println((rules.isAllowed(testPath) ? "allowed"
            : "not allowed") + ":\t" + testPath);
        testPath = testsIn.readLine();
      }
      testsIn.close();
    } catch (Exception e) {
      e.printStackTrace();
    }
  }
}