/*
    * 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.shardingsphere.proxy.backend.session;
  
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.List;
  import java.util.Map;
  import java.util.Map.Entry;
  import java.util.StringJoiner;
  import java.util.concurrent.ConcurrentHashMap;
  
  /**
   * This class only records variables need to be replayed on connections.
   */
  public final class RequiredSessionVariableRecorder {
      
      private static final String DEFAULT = "DEFAULT";
      
      private static final String NULL = "NULL";
      
      private final Map<String, String> sessionVariables = new ConcurrentHashMap<>();
      
      /**
       * Set variable.
       *
       * @param variableName variable name
       * @param variableValue variable value
       */
      public void setVariable(final String variableName, final String variableValue) {
          sessionVariables.put(variableName, variableValue);
      }
      
      /**
       * Return true if no session variable was set.
       *
       * @return true if no session variable was set
       */
      public boolean isEmpty() {
          return sessionVariables.isEmpty();
      }
      
      /**
       * Get set SQLs for database.
       *
       * @param databaseType database type
       * @return set SQLs
       */
      public List<String> toSetSQLs(final String databaseType) {
          if (sessionVariables.isEmpty()) {
              return Collections.emptyList();
          }
          // TODO Refactor the following switch by SPI if we support more database in future
          switch (databaseType) {
              case "MySQL":
                  return Collections.singletonList(aggregateToMySQLSetSQL());
              case "PostgreSQL":
                  return convertToPostgreSQLSetSQLs();
              default:
                  return Collections.emptyList();
          }
      }
      
      private String aggregateToMySQLSetSQL() {
          StringJoiner result = new StringJoiner(",", "SET ", "");
          for (Entry<String, String> entry : sessionVariables.entrySet()) {
              result.add(entry.getKey() + "=" + entry.getValue());
          }
          return result.toString();
      }
      
      private List<String> convertToPostgreSQLSetSQLs() {
          List<String> result = new ArrayList<>(sessionVariables.size());
          for (Entry<String, String> entry : sessionVariables.entrySet()) {
              result.add("SET " + entry.getKey() + "=" + entry.getValue());
          }
          return result;
      }
      
      /**
       * Get reset SQLs for database.
       *
       * @param databaseType database type
       * @return reset SQLs
      */
     public List<String> toResetSQLs(final String databaseType) {
         if (sessionVariables.isEmpty()) {
             return Collections.emptyList();
         }
         // TODO Refactor the following switch by SPI if we support more database in future
         switch (databaseType) {
             case "MySQL":
                 return Collections.singletonList(aggregateToMySQLSetDefaultSQLs());
             case "PostgreSQL":
                 return Collections.singletonList("RESET ALL");
             default:
                 return Collections.emptyList();
         }
     }
     
     private String aggregateToMySQLSetDefaultSQLs() {
         StringJoiner result = new StringJoiner(",", "SET ", "");
         for (String each : sessionVariables.keySet()) {
             if (each.startsWith("@")) {
                 result.add(each + "=" + NULL);
             } else {
                 result.add(each + "=" + DEFAULT);
             }
         }
         return result.toString();
     }
     
     /**
      * Remove variables with default value.
      */
     public void removeVariablesWithDefaultValue() {
         sessionVariables.entrySet().removeIf(entry -> DEFAULT.equalsIgnoreCase(entry.getValue()));
     }
 }