/**
 * 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.hcatalog.utils;

import java.io.IOException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;

import org.apache.hadoop.hive.ql.exec.UDFArgumentException;
import org.apache.hadoop.hive.ql.metadata.HiveException;
import org.apache.hadoop.hive.ql.udf.generic.GenericUDF;
import org.apache.hadoop.hive.serde2.objectinspector.ListObjectInspector;
import org.apache.hadoop.hive.serde2.objectinspector.MapObjectInspector;
import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspector;
import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspectorFactory;
import org.apache.hadoop.hive.serde2.objectinspector.PrimitiveObjectInspector;
import org.apache.hadoop.hive.serde2.objectinspector.StructField;
import org.apache.hadoop.hive.serde2.objectinspector.StructObjectInspector;
import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspector.Category;
import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspectorFactory.ObjectInspectorOptions;

/**
 * A hive udf to check types of the fields read from hcat. A sample hive query which can use this is:
 *
 * create temporary function typecheck as 'org.apache.hcatalog.utils.HCatTypeCheckHive';
 * select typecheck('map<string,string>+struct<num:int,str:string,dbl:double>+array<map<string,string>>+int', 
 * mymap, mytuple, bagofmap, rownum) from complex;
 *
 *
 * The first argument to the UDF is a string representing the schema of the columns in the table. 
 * The columns in the tables are the remaining args to it.
 * The schema specification consists of the types as given by "describe <table>"
 * with each column's type separated from the next column's type by a '+'
 *
 * The UDF will throw an exception (and cause the query to fail) if it does not
 * encounter the correct types.
 *
 * The output is a string representation of the data , type and hive category.
 * It is not advisable to use this against large dataset since the output would also
 * be large. 
 *
 */
public final class HCatTypeCheckHive extends GenericUDF {

    ObjectInspector[] argOIs;

    @Override
    public Object evaluate(DeferredObject[] args) throws HiveException {
        List<Object> row = new ArrayList<Object>();
        String typesStr = (String) getJavaObject(args[0].get(), argOIs[0], new ArrayList<Category>());
        String[] types = typesStr.split("\\+");
        for (int i = 0; i < types.length; i++) {
            types[i] = types[i].toLowerCase();
        }
        for (int i = 1; i < args.length; i++) {
            ObjectInspector oi = argOIs[i];
            List<ObjectInspector.Category> categories = new ArrayList<ObjectInspector.Category>();
            Object o = getJavaObject(args[i].get(), oi, categories);
            try {
                if (o != null) {
                    Util.check(types[i - 1], o);
                }
            } catch (IOException e) {
                throw new HiveException(e);
            }
            row.add(o == null ? "null" : o);
            row.add(":" + (o == null ? "null" : o.getClass()) + ":" + categories);
        }
        return row.toString();
    }

    private Object getJavaObject(Object o, ObjectInspector oi, List<Category> categories) {
        if (categories != null) {
            categories.add(oi.getCategory());
        }
        if (oi.getCategory() == ObjectInspector.Category.LIST) {
            List<?> l = ((ListObjectInspector) oi).getList(o);
            List<Object> result = new ArrayList<Object>();
            ObjectInspector elemOI = ((ListObjectInspector) oi).getListElementObjectInspector();
            for (Object lo : l) {
                result.add(getJavaObject(lo, elemOI, categories));
            }
            return result;
        } else if (oi.getCategory() == ObjectInspector.Category.MAP) {
            Map<?, ?> m = ((MapObjectInspector) oi).getMap(o);
            Map<String, String> result = new HashMap<String, String>();
            ObjectInspector koi = ((MapObjectInspector) oi).getMapKeyObjectInspector();
            ObjectInspector voi = ((MapObjectInspector) oi).getMapValueObjectInspector();
            for (Entry<?, ?> e : m.entrySet()) {
                result.put((String) getJavaObject(e.getKey(), koi, null),
                    (String) getJavaObject(e.getValue(), voi, null));
            }
            return result;

        } else if (oi.getCategory() == ObjectInspector.Category.STRUCT) {
            List<Object> s = ((StructObjectInspector) oi).getStructFieldsDataAsList(o);
            List<? extends StructField> sf = ((StructObjectInspector) oi).getAllStructFieldRefs();
            List<Object> result = new ArrayList<Object>();
            for (int i = 0; i < s.size(); i++) {
                result.add(getJavaObject(s.get(i), sf.get(i).getFieldObjectInspector(), categories));
            }
            return result;
        } else if (oi.getCategory() == ObjectInspector.Category.PRIMITIVE) {
            return ((PrimitiveObjectInspector) oi).getPrimitiveJavaObject(o);
        }
        throw new RuntimeException("Unexpected error!");
    }

    @Override
    public String getDisplayString(String[] arg0) {
        return null;
    }

    @Override
    public ObjectInspector initialize(ObjectInspector[] argOIs)
        throws UDFArgumentException {
        this.argOIs = argOIs;
        return ObjectInspectorFactory.getReflectionObjectInspector(String.class,
            ObjectInspectorOptions.JAVA);
    }

}