/*
    *    Copyright 2009-2023 the original author or authors.
    *
    *    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
    *
    *       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.ibatis.submitted.cursor_cache_oom;
  
  import java.io.IOException;
  import java.io.Reader;
  import java.lang.reflect.Field;
  import java.util.List;
  import java.util.Map;
  
  import org.apache.ibatis.BaseDataTest;
  import org.apache.ibatis.cache.CacheKey;
  import org.apache.ibatis.cursor.Cursor;
  import org.apache.ibatis.cursor.defaults.DefaultCursor;
  import org.apache.ibatis.executor.resultset.DefaultResultSetHandler;
  import org.apache.ibatis.io.Resources;
  import org.apache.ibatis.session.SqlSession;
  import org.apache.ibatis.session.SqlSessionFactory;
  import org.apache.ibatis.session.SqlSessionFactoryBuilder;
  import org.apache.ibatis.session.defaults.DefaultSqlSession;
  import org.junit.jupiter.api.Assertions;
  import org.junit.jupiter.api.BeforeAll;
  import org.junit.jupiter.api.Test;
  
  @SuppressWarnings("ALL")
  class CursorOomTest {
  
    private static SqlSessionFactory sqlSessionFactory;
  
    @BeforeAll
    static void setUp() throws Exception {
      // create an SqlSessionFactory
      try (Reader reader = Resources
          .getResourceAsReader("org/apache/ibatis/submitted/cursor_cache_oom/mybatis-config.xml")) {
        sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
      }
  
      // populate in-memory database
      BaseDataTest.runScript(sqlSessionFactory.getConfiguration().getEnvironment().getDataSource(),
          "org/apache/ibatis/submitted/cursor_cache_oom/CreateDB.sql");
    }
  
    private static Map<CacheKey, Object> getNestedResultObjects(Cursor<User> users)
        throws IllegalAccessException, NoSuchFieldException {
      DefaultCursor<User> defaultCursor = (DefaultCursor<User>) users;
      Field resultSetHandlerField = DefaultCursor.class.getDeclaredField("resultSetHandler");
      resultSetHandlerField.setAccessible(true);
      DefaultResultSetHandler defaultResultSetHandler = (DefaultResultSetHandler) resultSetHandlerField
          .get(defaultCursor);
      Field nestedResultObjectsField = DefaultResultSetHandler.class.getDeclaredField("nestedResultObjects");
      nestedResultObjectsField.setAccessible(true);
      return (Map<CacheKey, Object>) nestedResultObjectsField.get(defaultResultSetHandler);
    }
  
    private static List<Cursor<?>> getCursors(SqlSession sqlSession) throws NoSuchFieldException, IllegalAccessException {
      DefaultSqlSession session = (DefaultSqlSession) sqlSession;
      Field cursorListField = DefaultSqlSession.class.getDeclaredField("cursorList");
      cursorListField.setAccessible(true);
      List<Cursor<?>> cursorList = (List<Cursor<?>>) cursorListField.get(session);
      return cursorList;
    }
  
    @Test
    void shouldNotCacheAllDataForWholeSessionWhileUsingCursor()
        throws IOException, NoSuchFieldException, IllegalAccessException {
      try (SqlSession sqlSession = sqlSessionFactory.openSession()) {
        Mapper mapper = sqlSession.getMapper(Mapper.class);
        try (Cursor<User> users = mapper.fetchUsers()) {
          for (User user : users) {
            consumeUser(user);
          }
          Map nestedResultObjects = getNestedResultObjects(users);
  
          Assertions.assertFalse(nestedResultObjects.isEmpty());
  
          // does not pass now
          // will be great, if cursor will use constant memory instead of linear one
          // Assertions.assertTrue(nestedResultObjects.size() <= 2);
        }
  
        List<Cursor<?>> cursorList = getCursors(sqlSession);
  
        // expect that either reference to the cursor itselfis gone or cursor does not contains all the fetched data
        // the most preferrable way will be not to cache data, when the row is already processed (see commented
        // line above)
        Assertions
           .assertTrue(cursorList.isEmpty() || getNestedResultObjects((Cursor<User>) cursorList.get(0)).size() <= 2);
     }
   }
 
   private void consumeUser(User user) {
     // do nothing
   }
 }