/*
 * 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.knox.gateway.session.control;


import org.apache.knox.gateway.config.GatewayConfig;

import java.util.Map;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class ConcurrentSessionVerifier {
  public static final ConcurrentSessionVerifier INSTANCE = new ConcurrentSessionVerifier();
  private Set<String> privilegedUsers;
  private Set<String> nonPrivilegedUsers;
  private int privilegedUserConcurrentSessionLimit;
  private int nonPrivilegedUserConcurrentSessionLimit;
  private Map<String, Integer> concurrentSessionCounter;
  private final Lock sessionCountModifyLock = new ReentrantLock();

  private ConcurrentSessionVerifier() {
  }

  public static ConcurrentSessionVerifier getInstance() {
    return INSTANCE;
  }

  public void init(GatewayConfig config) {
    this.privilegedUsers = config.getPrivilegedUsers();
    this.nonPrivilegedUsers = config.getNonPrivilegedUsers();
    this.privilegedUserConcurrentSessionLimit = config.getPrivilegedUsersConcurrentSessionLimit();
    this.nonPrivilegedUserConcurrentSessionLimit = config.getNonPrivilegedUsersConcurrentSessionLimit();
    this.concurrentSessionCounter = new ConcurrentHashMap<>();
  }

  public boolean verifySessionForUser(String username) {
    if (!privilegedUsers.contains(username) && !nonPrivilegedUsers.contains(username)) {
      return true;
    }

    sessionCountModifyLock.lock();
    try {
      concurrentSessionCounter.putIfAbsent(username, 0);
      if (privilegedUserCheckLimitReached(username) || nonPrivilegedUserCheckLimitReached(username)) {
        return false;
      }
      concurrentSessionCounter.compute(username, (key, value) -> value + 1);
    } finally {
      sessionCountModifyLock.unlock();
    }
    return true;
  }

  private boolean privilegedUserCheckLimitReached(String username) {
    if (privilegedUserConcurrentSessionLimit < 0) {
      return false;
    }
    return privilegedUsers.contains(username) && (concurrentSessionCounter.get(username) >= privilegedUserConcurrentSessionLimit);
  }

  private boolean nonPrivilegedUserCheckLimitReached(String username) {
    if (nonPrivilegedUserConcurrentSessionLimit < 0) {
      return false;
    }
    return nonPrivilegedUsers.contains(username) && (concurrentSessionCounter.get(username) >= nonPrivilegedUserConcurrentSessionLimit);
  }

  public void sessionEndedForUser(String username) {
    sessionCountModifyLock.lock();
    try {
      concurrentSessionCounter.computeIfPresent(username, (key, counter) -> decreaseCounter(counter));
    } finally {
      sessionCountModifyLock.unlock();
    }
  }

  private Integer decreaseCounter(Integer counter) {
    counter--;
    if (counter < 1) {
      return null;
    } else {
      return counter;
    }
  }

  Integer getUserConcurrentSessionCount(String username) {
    return concurrentSessionCounter.get(username);
  }
}