/*
 * 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.phoenix.expression.function;

import java.sql.SQLException;
import java.util.List;
import org.apache.hadoop.hbase.io.ImmutableBytesWritable;
import org.apache.phoenix.expression.Expression;
import org.apache.phoenix.parse.FunctionParseNode.Argument;
import org.apache.phoenix.parse.FunctionParseNode.BuiltInFunction;
import org.apache.phoenix.schema.SortOrder;
import org.apache.phoenix.schema.tuple.Tuple;
import org.apache.phoenix.schema.types.PDataType;
import org.apache.phoenix.schema.types.PVarchar;
import org.apache.phoenix.util.StringUtil;

@BuiltInFunction(name = ReverseFunction.NAME,
    args = { @Argument(allowedTypes = { PVarchar.class }) })
public class ReverseFunction extends ScalarFunction {
  public static final String NAME = "REVERSE";

  public ReverseFunction() {
  }

  public ReverseFunction(List<Expression> children) throws SQLException {
    super(children);
  }

  @Override
  public boolean evaluate(Tuple tuple, ImmutableBytesWritable ptr) {
    Expression arg = getChildren().get(0);
    if (!arg.evaluate(tuple, ptr)) {
      return false;
    }

    int targetOffset = ptr.getLength();
    if (targetOffset == 0) {
      return true;
    }

    byte[] source = ptr.get();
    byte[] target = new byte[targetOffset];
    int sourceOffset = ptr.getOffset();
    int endOffset = sourceOffset + ptr.getLength();
    SortOrder sortOrder = arg.getSortOrder();
    while (sourceOffset < endOffset) {
      int nBytes = StringUtil.getBytesInChar(source[sourceOffset], sortOrder);
      targetOffset -= nBytes;
      System.arraycopy(source, sourceOffset, target, targetOffset, nBytes);
      sourceOffset += nBytes;
    }
    ptr.set(target);
    return true;
  }

  @Override
  public SortOrder getSortOrder() {
    return getChildren().get(0).getSortOrder();
  }

  @Override
  public PDataType getDataType() {
    return PVarchar.INSTANCE;
  }

  @Override
  public String getName() {
    return NAME;
  }

}
