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/*
 * Copyright 2016-2018 shardingsphere.io.
 * 
 * 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
 *
 *     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 io.shardingsphere.core.parsing;

import com.google.common.base.Optional;
import io.shardingsphere.core.constant.DatabaseType;
import io.shardingsphere.core.metadata.table.ShardingTableMetaData;
import io.shardingsphere.core.parsing.cache.ParsingResultCache;
import io.shardingsphere.core.parsing.lexer.LexerEngine;
import io.shardingsphere.core.parsing.lexer.LexerEngineFactory;
import io.shardingsphere.core.parsing.parser.sql.SQLParserFactory;
import io.shardingsphere.core.parsing.parser.sql.SQLStatement;
import io.shardingsphere.core.rule.ShardingRule;
import lombok.RequiredArgsConstructor;

/**
 * SQL parsing engine.
 *
 * @author zhangliang
 */
@RequiredArgsConstructor
public final class SQLParsingEngine {
    
    private final DatabaseType dbType;
    
    private final String sql;
    
    private final ShardingRule shardingRule;
    
    private final ShardingTableMetaData shardingTableMetaData;
    
    /**
     * Parse SQL.
     * 
     * @param useCache use cache or not
     * @return parsed SQL statement
     */
    public SQLStatement parse(final boolean useCache) {
        Optional cachedSQLStatement = getSQLStatementFromCache(useCache);
        if (cachedSQLStatement.isPresent()) {
            return cachedSQLStatement.get();
        }
        LexerEngine lexerEngine = LexerEngineFactory.newInstance(dbType, sql);
        lexerEngine.nextToken();
        SQLStatement result = SQLParserFactory.newInstance(dbType, lexerEngine.getCurrentToken().getType(), shardingRule, lexerEngine, shardingTableMetaData).parse();
        if (useCache) {
            ParsingResultCache.getInstance().put(sql, result);
        }
        return result;
    }
    
    private Optional getSQLStatementFromCache(final boolean useCache) {
        return useCache ? Optional.fromNullable(ParsingResultCache.getInstance().getSQLStatement(sql)) : Optional.absent();
    }
}