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/*
 *
 * 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 org.apache.hive.storage.jdbc;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.hive.ql.plan.ExprNodeColumnDesc;
import org.apache.hadoop.hive.ql.plan.ExprNodeDesc;
import org.apache.hadoop.hive.ql.plan.TableScanDesc;
import org.apache.hadoop.hive.serde.serdeConstants;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import org.apache.hive.storage.jdbc.conf.JdbcStorageConfig;

import java.beans.XMLDecoder;
import java.io.ByteArrayInputStream;
import java.util.HashMap;
import java.util.Map;

/**
 * Translates the hive query condition into a condition that can be run on the underlying database
 */
public class QueryConditionBuilder {

  private static final Logger LOGGER = LoggerFactory.getLogger(QueryConditionBuilder.class);
  private static final String EMPTY_STRING = "";
  private static QueryConditionBuilder instance = null;


  public static QueryConditionBuilder getInstance() {
    if (instance == null) {
      instance = new QueryConditionBuilder();
    }

    return instance;
  }


  private QueryConditionBuilder() {

  }


  public String buildCondition(Configuration conf) {
    if (conf == null) {
      return EMPTY_STRING;
    }

    String filterXml = conf.get(TableScanDesc.FILTER_EXPR_CONF_STR);
    String hiveColumns = conf.get(serdeConstants.LIST_COLUMNS);
    String columnMapping = conf.get(JdbcStorageConfig.COLUMN_MAPPING.getPropertyName());

    if ((filterXml == null) || ((columnMapping == null) && (hiveColumns == null))) {
      return EMPTY_STRING;
    }

    if (hiveColumns == null) {
      hiveColumns = "";
    }

    Map columnMap = buildColumnMapping(columnMapping, hiveColumns);
    String condition = createConditionString(filterXml, columnMap);
    return condition;
  }


  /*
   * Build a Hive-to-X column mapping,
   *
   */
  private Map buildColumnMapping(String columnMapping, String hiveColumns) {
    if ((columnMapping == null) || (columnMapping.trim().isEmpty())) {
      return createIdentityMap(hiveColumns);
    }

    Map columnMap = new HashMap();
    String[] mappingPairs = columnMapping.toLowerCase().split(",");
    for (String mapPair : mappingPairs) {
      String[] columns = mapPair.split("=");
      columnMap.put(columns[0].trim(), columns[1].trim());
    }

    return columnMap;
  }


  /*
   * When no mapping is defined, it is assumed that the hive column names are equivalent to the column names in the
   * underlying table
   */
  private Map createIdentityMap(String hiveColumns) {
    Map columnMap = new HashMap();
    String[] columns = hiveColumns.toLowerCase().split(",");

    for (String col : columns) {
      columnMap.put(col.trim(), col.trim());
    }

    return columnMap;
  }


  /*
   * Walk to Hive AST and translate the hive column names to their equivalent mappings. This is basically a cheat.
   *
   */
  private String createConditionString(String filterXml, Map columnMap) {
    if ((filterXml == null) || (filterXml.trim().isEmpty())) {
      return EMPTY_STRING;
    }

    try (XMLDecoder decoder = new XMLDecoder(new ByteArrayInputStream(filterXml.getBytes("UTF-8")))) {
      Object object = decoder.readObject();
      if (!(object instanceof ExprNodeDesc)) {
        LOGGER.error("Deserialized filter expression is not of the expected type");
        throw new RuntimeException("Deserialized filter expression is not of the expected type");
      }

      ExprNodeDesc conditionNode = (ExprNodeDesc) object;
      walkTreeAndTranslateColumnNames(conditionNode, columnMap);
      return conditionNode.getExprString();
    }
    catch (Exception e) {
      LOGGER.error("Error during condition build", e);
      return EMPTY_STRING;
    }
  }


  /*
   * Translate column names by walking the AST
   */
  private void walkTreeAndTranslateColumnNames(ExprNodeDesc node, Map columnMap) {
    if (node == null) {
      return;
    }

    if (node instanceof ExprNodeColumnDesc) {
      ExprNodeColumnDesc column = (ExprNodeColumnDesc) node;
      String hiveColumnName = column.getColumn().toLowerCase();
      if (columnMap.containsKey(hiveColumnName)) {
        String dbColumnName = columnMap.get(hiveColumnName);
        String finalName = formatColumnName(dbColumnName);
        column.setColumn(finalName);
      }
    }
    else {
      if (node.getChildren() != null) {
        for (ExprNodeDesc childNode : node.getChildren()) {
          walkTreeAndTranslateColumnNames(childNode, columnMap);
        }
      }
    }
  }


  /**
   * This is an ugly hack for handling date column types because Hive doesn't have a built-in type for dates
   */
  private String formatColumnName(String dbColumnName) {
    if (dbColumnName.contains(":")) {
      String[] typeSplit = dbColumnName.split(":");

      if (typeSplit[1].equalsIgnoreCase("date")) {
        return "{d " + typeSplit[0] + "}";
      }

      return typeSplit[0];
    }
    else {
      return dbColumnName;
    }
  }
}