/**
 * 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.FunctionRegistry;
import org.apache.hadoop.hive.ql.exec.UDFArgumentException;
import org.apache.hadoop.hive.ql.exec.UDFArgumentLengthException;
import org.apache.hadoop.hive.ql.metadata.HiveException;
import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspector;
import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspectorConverters;
import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspectorConverters.Converter;
import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspectorUtils;
import org.apache.hadoop.hive.serde2.typeinfo.PrimitiveTypeInfo;
import org.apache.hadoop.hive.serde2.typeinfo.TypeInfo;
import org.apache.hadoop.hive.serde2.typeinfo.TypeInfoFactory;
import org.apache.hadoop.hive.serde2.typeinfo.TypeInfoUtils;


/**
 * Base class for comparison UDF's (Greatest and Least).
 */
public abstract class GenericUDFBaseNwayCompare extends GenericUDF {

  protected transient ObjectInspector[] argumentOIs;
  protected transient Converter[] converters;
  protected transient ObjectInspector resultOI;

  /**
   * @return desired comparison (positive for greatest, negative for least)
   */
  abstract int getOrder();

  @Override
  public ObjectInspector initialize(ObjectInspector[] arguments) throws UDFArgumentException {
    if (arguments.length < 2) {
      throw new UDFArgumentLengthException(getFuncName() + " requires at least 2 arguments, got "
        + arguments.length);
    }
    if (arguments[0].getCategory() != ObjectInspector.Category.PRIMITIVE) {
      throw new UDFArgumentException(getFuncName() + " only takes primitive types, got "
        + arguments[0].getTypeName());
    }

    argumentOIs = arguments;
    converters = new Converter[arguments.length];

    TypeInfo commonInfo = TypeInfoUtils.getTypeInfoFromObjectInspector(arguments[0]);

    for (int i = 1; i < arguments.length; i++) {
      PrimitiveTypeInfo currInfo = (PrimitiveTypeInfo) TypeInfoUtils.getTypeInfoFromObjectInspector(arguments[i]);

      commonInfo = FunctionRegistry.getCommonClassForComparison(
        commonInfo, currInfo);
    }

    resultOI = TypeInfoUtils.getStandardWritableObjectInspectorFromTypeInfo(
      (commonInfo == null) ?
        TypeInfoFactory.doubleTypeInfo : commonInfo);

    for (int i = 0; i < arguments.length; i++) {
      converters[i] = ObjectInspectorConverters.getConverter(arguments[i], resultOI);
    }

    return resultOI;
  }

  @SuppressWarnings({ "rawtypes", "unchecked" })
  @Override
  public Object evaluate(GenericUDF.DeferredObject[] arguments) throws HiveException {
    Object maxV = null;
    //for case of conversion, convert both values to common type and then compare.
    for (int i = 0; i < arguments.length; i++) {
      Object ai = arguments[i].get();
      if (ai == null) { //NULL if any of the args are nulls
        return null;
      }

      if (maxV == null) { //First non-null item.
        maxV = converters[i].convert(ai);
        continue;
      }
      Object converted = converters[i].convert(ai);
      if (converted == null) {
        return null;
      }
      int result = ObjectInspectorUtils.compare(
        converted, resultOI,
        maxV, resultOI);
      if (getOrder() * result > 0) {
        maxV = converted;
      }
    }
    return maxV;
  }

  @Override
  public String getDisplayString(String[] children) {
    return getStandardDisplayString(getFuncName(), children, ",");
  }
}