// Copyright (C) 2016 The Android Open Source Project
//
// Licensed 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 com.google.gerrit.server.mail.receive;

import com.google.common.flogger.FluentLogger;
import com.google.common.primitives.Ints;
import com.google.gerrit.mail.MailMessage;
import com.google.gerrit.mail.MailParsingException;
import com.google.gerrit.mail.RawMailParser;
import com.google.gerrit.server.git.WorkQueue;
import com.google.gerrit.server.mail.EmailSettings;
import com.google.gerrit.server.mail.Encryption;
import com.google.inject.Inject;
import com.google.inject.Singleton;
import java.io.BufferedReader;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import org.apache.commons.net.pop3.POP3Client;
import org.apache.commons.net.pop3.POP3MessageInfo;
import org.apache.commons.net.pop3.POP3SClient;

/** An implementation of {@link MailReceiver} for POP3. */
@Singleton
public class Pop3MailReceiver extends MailReceiver {
  private static final FluentLogger logger = FluentLogger.forEnclosingClass();

  @Inject
  Pop3MailReceiver(EmailSettings mailSettings, MailProcessor mailProcessor, WorkQueue workQueue) {
    super(mailSettings, mailProcessor, workQueue);
  }

  /**
   * Opens a connection to the mail server, removes emails where deletion is pending, reads new
   * email and closes the connection.
   *
   * @param async determines if processing messages should happen asynchronously
   * @throws MailTransferException in case of a known transport failure
   * @throws IOException in case of a low-level transport failure
   */
  @Override
  public synchronized void handleEmails(boolean async) throws MailTransferException, IOException {
    POP3Client pop3;
    if (mailSettings.encryption != Encryption.NONE) {
      pop3 = new POP3SClient(mailSettings.encryption.name(), true);
    } else {
      pop3 = new POP3Client();
    }
    if (mailSettings.port > 0) {
      pop3.setDefaultPort(mailSettings.port);
    }
    pop3.connect(mailSettings.host);
    try {
      if (!pop3.login(mailSettings.username, mailSettings.password)) {
        throw new MailTransferException(
            "Could not login to POP3 email server. Check username and password");
      }
      try {
        POP3MessageInfo[] messages = pop3.listMessages();
        if (messages == null) {
          throw new MailTransferException("Could not retrieve message list via POP3");
        }
        logger.atInfo().log("Received %d messages via POP3", messages.length);
        // Fetch messages
        List<MailMessage> mailMessages = new ArrayList<>();
        for (POP3MessageInfo msginfo : messages) {
          if (msginfo == null) {
            // Message was deleted
            continue;
          }
          try (BufferedReader reader = (BufferedReader) pop3.retrieveMessage(msginfo.number)) {
            if (reader == null) {
              throw new MailTransferException(
                  "Could not retrieve POP3 message header for message " + msginfo.identifier);
            }
            int[] message = fetchMessage(reader);
            MailMessage mailMessage = RawMailParser.parse(message);
            // Delete messages where deletion is pending. This requires
            // knowing the integer message ID of the email. We therefore parse
            // the message first and extract the Message-ID specified in RFC
            // 822 and delete the message if deletion is pending.
            if (pendingDeletion.contains(mailMessage.id())) {
              if (pop3.deleteMessage(msginfo.number)) {
                pendingDeletion.remove(mailMessage.id());
              } else {
                logger.atSevere().log("Could not delete message %d", msginfo.number);
              }
            } else {
              // Process message further
              mailMessages.add(mailMessage);
            }
          } catch (MailParsingException e) {
            logger.atSevere().log("Could not parse message %d", msginfo.number);
          }
        }
        dispatchMailProcessor(mailMessages, async);
      } finally {
        pop3.logout();
      }
    } finally {
      pop3.disconnect();
    }
  }

  public final int[] fetchMessage(BufferedReader reader) throws IOException {
    List<Integer> character = new ArrayList<>();
    int ch;
    while ((ch = reader.read()) != -1) {
      character.add(ch);
    }
    return Ints.toArray(character);
  }
}