/*
    * 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
    *
    *     https://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.commons.configuration2.sync;
  
  import static org.junit.jupiter.api.Assertions.assertEquals;
  import static org.mockito.Mockito.mock;
  import static org.mockito.Mockito.verify;
  import static org.mockito.Mockito.verifyNoMoreInteractions;
  import static org.mockito.Mockito.when;
  
  import java.util.Random;
  import java.util.concurrent.locks.Lock;
  import java.util.concurrent.locks.ReadWriteLock;
  
  import org.junit.jupiter.api.Test;
  
  /**
   * Test class for {@code ReadWriteSynchronizer}.
   */
  public class TestReadWriteSynchronizer {
      /**
       * A class representing an account.
       */
      private static final class Account {
          /** The amount stored in this account. */
          private long amount;
  
          /**
           * Changes the amount of money by the given delata.
           *
           * @param delta the delta
           */
          public void change(final long delta) {
              amount += delta;
          }
  
          /**
           * Returns the amount of money stored in this account.
           *
           * @return the amount
           */
          public long getAmount() {
              return amount;
          }
      }
  
      /**
       * A thread which performs a number of read operations on the bank's accounts and checks whether the amount of money is
       * consistent.
       */
      private static final class ReaderThread extends Thread {
          /** The acounts to monitor. */
          private final Account[] accounts;
  
          /** The synchronizer object. */
          private final Synchronizer sync;
  
          /** The number of read operations. */
          private final int numberOfReads;
  
          /** Stores errors detected on read operations. */
          private volatile int errors;
  
          /**
           * Creates a new instance of {@code ReaderThread}.
           *
           * @param s the synchronizer to be used
           * @param readCount the number of read operations
           * @param accs the accounts to monitor
           */
          public ReaderThread(final Synchronizer s, final int readCount, final Account... accs) {
              accounts = accs;
              sync = s;
              numberOfReads = readCount;
          }
  
          /**
           * Returns the number of errors occurred during read operations.
           *
           * @return the number of errors
           */
          public int getErrors() {
              return errors;
          }
  
         /**
          * Performs the given number of read operations.
          */
         @Override
         public void run() {
             for (int i = 0; i < numberOfReads; i++) {
                 sync.beginRead();
                 final long sum = sumUpAccounts(accounts);
                 sync.endRead();
                 if (sum != TOTAL_MONEY) {
                     errors++;
                 }
             }
         }
     }
 
     /**
      * A test thread for updating account objects. This thread executes a number of transactions on two accounts. Each
      * transaction determines the account containing more money. Then a random number of money is transferred from this
      * account to the other one.
      */
     private static final class UpdateThread extends Thread {
         /** The synchronizer. */
         private final Synchronizer sync;
 
         /** Account 1. */
         private final Account account1;
 
         /** Account 2. */
         private final Account account2;
 
         /** An object for creating random numbers. */
         private final Random random;
 
         /** The number of transactions. */
         private final int numberOfUpdates;
 
         /**
          * Creates a new instance of {@code UpdateThread}.
          *
          * @param s the synchronizer
          * @param updateCount the number of updates
          * @param ac1 account 1
          * @param ac2 account 2
          */
         public UpdateThread(final Synchronizer s, final int updateCount, final Account ac1, final Account ac2) {
             sync = s;
             account1 = ac1;
             account2 = ac2;
             numberOfUpdates = updateCount;
             random = new Random();
         }
 
         /**
          * Performs the given number of update transactions.
          */
         @Override
         public void run() {
             for (int i = 0; i < numberOfUpdates; i++) {
                 sync.beginWrite();
                 final Account acSource;
                 Account acDest;
                 if (account1.getAmount() < account2.getAmount()) {
                     acSource = account1;
                     acDest = account2;
                 } else {
                     acSource = account2;
                     acDest = account1;
                 }
                 final long x = Math.round(random.nextDouble() * (acSource.getAmount() - 1)) + 1;
                 acSource.change(-x);
                 acDest.change(x);
                 sync.endWrite();
             }
         }
     }
 
     /** Constant for the total amount of money in the system. */
     private static final long TOTAL_MONEY = 1000000L;
 
     /**
      * Helper method to calculate the sum over all accounts.
      *
      * @param accounts the accounts to check
      * @return the sum of the money on these accounts
      */
     private static long sumUpAccounts(final Account... accounts) {
         long sum = 0;
         for (final Account acc : accounts) {
             sum += acc.getAmount();
         }
         return sum;
     }
 
     /**
      * Tests whether a lock passed to the constructor is used.
      */
     @Test
     void testInitLock() {
         final ReadWriteLock lock = mock(ReadWriteLock.class);
         final Lock readLock = mock(Lock.class);
 
         when(lock.readLock()).thenReturn(readLock);
 
         final ReadWriteSynchronizer sync = new ReadWriteSynchronizer(lock);
         sync.beginRead();
 
         verify(lock).readLock();
         verify(readLock).lock();
         verifyNoMoreInteractions(lock, readLock);
     }
 
     /**
      * Tests whether the synchronizer is reentrant. This is important for some combined operations on a configuration.
      */
     @Test
     void testReentrance() {
         final Synchronizer sync = new ReadWriteSynchronizer();
         sync.beginWrite();
         sync.beginRead();
         sync.beginRead();
         sync.endRead();
         sync.endRead();
         sync.beginWrite();
         sync.endWrite();
         sync.endWrite();
     }
 
     /**
      * Performs a test of the synchronizer based on the classic example of account objects. Money is transferred between two
      * accounts. If everything goes well, the total amount of money stays constant over time.
      */
     @Test
     void testSynchronizerInAction() throws InterruptedException {
         final int numberOfUpdates = 10000;
         final int numberOfReads = numberOfUpdates / 2;
         final int readThreadCount = 3;
         final int updateThreadCount = 2;
 
         final Synchronizer sync = new ReadWriteSynchronizer();
         final Account account1 = new Account();
         final Account account2 = new Account();
         account1.change(TOTAL_MONEY / 2);
         account2.change(TOTAL_MONEY / 2);
 
         final UpdateThread[] updateThreads = new UpdateThread[updateThreadCount];
         for (int i = 0; i < updateThreads.length; i++) {
             updateThreads[i] = new UpdateThread(sync, numberOfUpdates, account1, account2);
             updateThreads[i].start();
         }
         final ReaderThread[] readerThreads = new ReaderThread[readThreadCount];
         for (int i = 0; i < readerThreads.length; i++) {
             readerThreads[i] = new ReaderThread(sync, numberOfReads, account1, account2);
             readerThreads[i].start();
         }
 
         for (final UpdateThread t : updateThreads) {
             t.join();
         }
         for (final ReaderThread t : readerThreads) {
             t.join();
             assertEquals(0, t.getErrors());
         }
         sync.beginRead();
         assertEquals(TOTAL_MONEY, sumUpAccounts(account1, account2));
         sync.endRead();
     }
 }