/**
 * 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.hadoop.hive.ql.udf.generic;

import org.apache.hadoop.hive.ql.exec.UDFArgumentException;
import org.apache.hadoop.hive.ql.exec.UDFArgumentLengthException;
import org.apache.hadoop.hive.ql.exec.UDFArgumentTypeException;
import org.apache.hadoop.hive.ql.metadata.HiveException;
import org.apache.hadoop.hive.serde.Constants;
import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspector;
import org.apache.hadoop.hive.serde2.objectinspector.PrimitiveObjectInspector;
import org.apache.hadoop.hive.serde2.objectinspector.primitive.BooleanObjectInspector;

/**
 * IF(expr1,expr2,expr3) <br>
 * If expr1 is TRUE (expr1 <> 0 and expr1 <> NULL) then IF() returns expr2;
 * otherwise it returns expr3. IF() returns a numeric or string value, depending
 * on the context in which it is used.
 */
public class GenericUDFIf extends GenericUDF {
  private ObjectInspector[] argumentOIs;
  private GenericUDFUtils.ReturnObjectInspectorResolver returnOIResolver;

  @Override
  public ObjectInspector initialize(ObjectInspector[] arguments) throws UDFArgumentException {
    argumentOIs = arguments;
    returnOIResolver = new GenericUDFUtils.ReturnObjectInspectorResolver(true);

    if (arguments.length != 3) {
      throw new UDFArgumentLengthException(
          "The function IF(expr1,expr2,expr3) accepts exactly 3 arguments.");
    }

    boolean conditionTypeIsOk = (arguments[0].getCategory() == ObjectInspector.Category.PRIMITIVE);
    if (conditionTypeIsOk) {
      PrimitiveObjectInspector poi = ((PrimitiveObjectInspector) arguments[0]);
      conditionTypeIsOk = (poi.getPrimitiveCategory() == PrimitiveObjectInspector.PrimitiveCategory.BOOLEAN
          || poi.getPrimitiveCategory() == PrimitiveObjectInspector.PrimitiveCategory.VOID);
    }
    if (!conditionTypeIsOk) {
      throw new UDFArgumentTypeException(0,
          "The first argument of function IF should be \""
          + Constants.BOOLEAN_TYPE_NAME + "\", but \""
          + arguments[0].getTypeName() + "\" is found");
    }

    if (!(returnOIResolver.update(arguments[1]) && returnOIResolver
        .update(arguments[2]))) {
      throw new UDFArgumentTypeException(2,
          "The second and the third arguments of function IF should have the same type, "
          + "but they are different: \"" + arguments[1].getTypeName()
          + "\" and \"" + arguments[2].getTypeName() + "\"");
    }

    return returnOIResolver.get();
  }

  @Override
  public Object evaluate(DeferredObject[] arguments) throws HiveException {
    Object condition = arguments[0].get();
    if (condition != null
        && ((BooleanObjectInspector) argumentOIs[0]).get(condition)) {
      return returnOIResolver.convertIfNecessary(arguments[1].get(),
          argumentOIs[1]);
    } else {
      return returnOIResolver.convertIfNecessary(arguments[2].get(),
          argumentOIs[2]);
    }
  }

  @Override
  public String getDisplayString(String[] children) {
    assert (children.length == 3);
    StringBuilder sb = new StringBuilder();
    sb.append("if(");
    sb.append(children[0]).append(", ");
    sb.append(children[1]).append(", ");
    sb.append(children[2]).append(")");
    return sb.toString();
  }

}