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/*
 *    Copyright 2018 University of Michigan
 *
 *    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.verdictdb.sqlsyntax;

import java.util.Collection;
import java.util.List;

import com.google.common.collect.Lists;

public class PrestoSyntax extends SqlSyntax {

  @Override
  public Collection getCandidateJDBCDriverClassNames() {
    List candidates = Lists.newArrayList("com.facebook.presto.jdbc.PrestoDriver");
    return candidates;
  }

  @Override
  public boolean doesSupportTablePartitioning() {
    return false;
  }

  @Override
  public void dropTable(String schema, String tablename) {}

  @Override
  public int getColumnNameColumnIndex() {
    return 0;
  }

  @Override
  public String getColumnsCommand(String schema, String table) {
    return "DESCRIBE " + quoteName(schema) + "." + quoteName(table);
  }

  @Override
  public String getFallbackDefaultSchema() {
    return "default";
  }

  @Override
  public int getColumnTypeColumnIndex() {
    return 1;
  }

  @Override
  public String getPartitionByInCreateTable(
      List partitionColumns, List partitionCounts) {
    StringBuilder sql = new StringBuilder();
    sql.append("partitioned_by = ARRAY");
    sql.append(" [");
    boolean isFirstColumn = true;
    for (String col : partitionColumns) {
      if (isFirstColumn) {
        sql.append(quoteName(col));
        isFirstColumn = false;
      } else {
        sql.append(", " + quoteName(col));
      }
    }
    sql.append("], ");
    return sql.toString();
  }

  /** This command also returns partition information if exists */
  @Override
  public String getPartitionCommand(String schema, String table) {
    return "DESCRIBE " + quoteName(schema) + "." + quoteName(table);
    //    return "SHOW PARTITIONS " + quoteName(schema) + "." + quoteName(table);
  }

  @Override
  public String getQuoteString() {
    return "\"";
  }

  @Override
  public String getSchemaCommand() {
    return "SHOW SCHEMAS";
  }

  @Override
  public int getSchemaNameColumnIndex() {
    return 0;
  }

  @Override
  public String getTableCommand(String schema) {
    return "SHOW TABLES IN " + quoteName(schema);
  }

  @Override
  public int getTableNameColumnIndex() {
    return 0;
  }

  @Override
  public String randFunction() {
    return "rand()";
  }

  @Override
  public boolean isAsRequiredBeforeSelectInCreateTable() {
    return true;
  }

  @Override
  public boolean equals(Object obj) {
    if (obj == null) {
      return false;
    }
    if (obj == this) {
      return true;
    }
    if (obj.getClass() != getClass()) {
      return false;
    }
    return true;
  }

  @Override
  public String getGenericStringDataTypeName() {
    return "VARCHAR";
  }

  @Override
  public String getApproximateCountDistinct(String column) {
    return String.format("approx_distinct(%s)", column);
  }

  /**
   * The following query returns 9.724487470589725 (9.72 / 100 = 0.0972):
   * 
   * select stddev(c)
   * from (
   *     select v, count(*) as c
   *     from (
   *         select from_base(substr(to_hex(md5(to_utf8(cast(value as varchar)))), 1, 8), 16) % 100 as v
   *         from mytable
   *     ) t1
   *     group by v
   * ) t2
   * 
   * where mytable contains the integers from 0 to 10000.
   * 
   * Note that the stddev of rand() is sqrt(0.01 * 0.99) = 0.09949874371.
   * 
   * I alss tested xxhash64(); however, its std was larger (i.e., 10.243500033157268).
   * 
   * Now I test xxhash64() for faster speed.
   */
  @Override
  public String hashFunction(String column) {
//    String f = String.format(
//        "(from_base(substr(to_hex(md5(to_utf8(cast(%s as varchar)))), 1, 8), 16) %% %d) / %d",
//        column, hashPrecision, hashPrecision);
    String f = String.format(
        "(from_base(substr(to_hex(xxhash64(to_utf8(cast(%s as varchar)))), 1, 8), 16) %% %d) "
        + "/ cast(%d as double)",
        column, hashPrecision, hashPrecision);
    return f;
  }
}