/*
    * 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.mysql.handler.admin.executor;
  
  import lombok.Getter;
  import lombok.RequiredArgsConstructor;
  import org.apache.shardingsphere.authority.checker.AuthorityChecker;
  import org.apache.shardingsphere.authority.rule.AuthorityRule;
  import org.apache.shardingsphere.infra.executor.sql.execute.result.query.QueryResultMetaData;
  import org.apache.shardingsphere.infra.executor.sql.execute.result.query.impl.raw.metadata.RawQueryResultColumnMetaData;
  import org.apache.shardingsphere.infra.executor.sql.execute.result.query.impl.raw.metadata.RawQueryResultMetaData;
  import org.apache.shardingsphere.infra.merge.result.MergedResult;
  import org.apache.shardingsphere.infra.merge.result.impl.local.LocalDataMergedResult;
  import org.apache.shardingsphere.infra.merge.result.impl.local.LocalDataQueryResultRow;
  import org.apache.shardingsphere.infra.util.regex.RegexUtils;
  import org.apache.shardingsphere.proxy.backend.context.ProxyContext;
  import org.apache.shardingsphere.proxy.backend.handler.admin.executor.DatabaseAdminQueryExecutor;
  import org.apache.shardingsphere.proxy.backend.session.ConnectionSession;
  import org.apache.shardingsphere.sql.parser.sql.dialect.statement.mysql.dal.MySQLShowDatabasesStatement;
  
  import java.sql.Types;
  import java.util.Collection;
  import java.util.Collections;
  import java.util.Optional;
  import java.util.stream.Collectors;
  
  /**
   * Show databases executor.
   */
  @RequiredArgsConstructor
  @Getter
  public final class ShowDatabasesExecutor implements DatabaseAdminQueryExecutor {
      
      private final MySQLShowDatabasesStatement showDatabasesStatement;
      
      private MergedResult mergedResult;
      
      @Override
      public void execute(final ConnectionSession connectionSession) {
          mergedResult = new LocalDataMergedResult(getDatabaseNames(connectionSession));
      }
      
      private Collection<LocalDataQueryResultRow> getDatabaseNames(final ConnectionSession connectionSession) {
          AuthorityRule authorityRule = ProxyContext.getInstance().getContextManager().getMetaDataContexts().getMetaData().getGlobalRuleMetaData().getSingleRule(AuthorityRule.class);
          AuthorityChecker authorityChecker = new AuthorityChecker(authorityRule, connectionSession.getGrantee());
          return ProxyContext.getInstance().getAllDatabaseNames().stream().sorted()
                  .filter(each -> checkLikePattern(each) && authorityChecker.isAuthorized(each)).map(LocalDataQueryResultRow::new).collect(Collectors.toList());
      }
      
      private boolean checkLikePattern(final String databaseName) {
          if (showDatabasesStatement.getFilter().isPresent()) {
              Optional<String> pattern = showDatabasesStatement.getFilter().get().getLike().map(optional -> RegexUtils.convertLikePatternToRegex(optional.getPattern()));
              return !pattern.isPresent() || databaseName.matches(pattern.get());
          }
          return true;
      }
      
      @Override
      public QueryResultMetaData getQueryResultMetaData() {
          return new RawQueryResultMetaData(Collections.singletonList(new RawQueryResultColumnMetaData("SCHEMATA", "SCHEMA_NAME", "Database", Types.VARCHAR, "VARCHAR", 255, 0)));
      }
  }