<?php

/**
 * @file
 * Database interface code for MySQL database servers.
 */

/**
 * @ingroup database
 * @{
 */

class DatabaseConnection_mysql extends DatabaseConnection {

  /**
   * Flag to indicate if we have registered the nextID cleanup function.
   *
   * @var boolean
   */
  protected $shutdownRegistered = FALSE;

  public function __construct(array $connection_options = array()) {
    // This driver defaults to transaction support, except if explicitly passed FALSE.
    $this->transactionSupport = !isset($connection_options['transactions']) || ($connection_options['transactions'] !== FALSE);

    // MySQL never supports transactional DDL.
    $this->transactionalDDLSupport = FALSE;

    $this->connectionOptions = $connection_options;

    // The DSN should use either a socket or a host/port.
    if (isset($connection_options['unix_socket'])) {
      $dsn = 'mysql:unix_socket=' . $connection_options['unix_socket'];
    }
    else {
      // Default to TCP connection on port 3306.
      $dsn = 'mysql:host=' . $connection_options['host'] . ';port=' . (empty($connection_options['port']) ? 3306 : $connection_options['port']);
    }
    $dsn .= ';dbname=' . $connection_options['database'];
    parent::__construct($dsn, $connection_options['username'], $connection_options['password'], array(
      // So we don't have to mess around with cursors and unbuffered queries by default.
      PDO::MYSQL_ATTR_USE_BUFFERED_QUERY => TRUE,
      // Because MySQL's prepared statements skip the query cache, because it's dumb.
      PDO::ATTR_EMULATE_PREPARES => TRUE,
      // Force column names to lower case.
      PDO::ATTR_CASE => PDO::CASE_LOWER,
    ));

    // Force MySQL to use the UTF-8 character set. Also set the collation, if a
    // certain one has been set; otherwise, MySQL defaults to 'utf8_general_ci'
    // for UTF-8.
    if (!empty($connection_options['collation'])) {
      $this->exec('SET NAMES utf8 COLLATE ' . $connection_options['collation']);
    }
    else {
      $this->exec('SET NAMES utf8');
    }

    // Force MySQL's behavior to conform more closely to SQL standards.
    // This allows Drupal to run almost seamlessly on many different
    // kinds of database systems. These settings force MySQL to behave
    // the same as postgresql, or sqlite in regards to syntax interpretation
    // and invalid data handling. See http://drupal.org/node/344575 for
    // further discussion. Also, as MySQL 5.5 changed the meaning of
    // TRADITIONAL we need to spell out the modes one by one.
    $this->exec("SET sql_mode='ANSI,STRICT_TRANS_TABLES,STRICT_ALL_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER'");
  }

  public function queryRange($query, $from, $count, array $args = array(), array $options = array()) {
    return $this->query($query . ' LIMIT ' . (int) $from . ', ' . (int) $count, $args, $options);
  }

  public function queryTemporary($query, array $args = array(), array $options = array()) {
    $tablename = $this->generateTemporaryTableName();
    $this->query(preg_replace('/^SELECT/i', 'CREATE TEMPORARY TABLE {' . $tablename . '} Engine=MEMORY SELECT', $query), $args, $options);
    return $tablename;
  }

  public function driver() {
    return 'mysql';
  }

  public function databaseType() {
    return 'mysql';
  }

  public function mapConditionOperator($operator) {
    // We don't want to override any of the defaults.
    return NULL;
  }

  public function nextId($existing_id = 0) {
    $new_id = $this->query('INSERT INTO {sequences} () VALUES ()', array(), array('return' => Database::RETURN_INSERT_ID));
    // This should only happen after an import or similar event.
    if ($existing_id >= $new_id) {
      // If we INSERT a value manually into the sequences table, on the next
      // INSERT, MySQL will generate a larger value. However, there is no way
      // of knowing whether this value already exists in the table. MySQL
      // provides an INSERT IGNORE which would work, but that can mask problems
      // other than duplicate keys. Instead, we use INSERT ... ON DUPLICATE KEY
      // UPDATE in such a way that the UPDATE does not do anything. This way,
      // duplicate keys do not generate errors but everything else does.
      $this->query('INSERT INTO {sequences} (value) VALUES (:value) ON DUPLICATE KEY UPDATE value = value', array(':value' => $existing_id));
      $new_id = $this->query('INSERT INTO {sequences} () VALUES ()', array(), array('return' => Database::RETURN_INSERT_ID));
    }
    if (!$this->shutdownRegistered) {
      // Use register_shutdown_function() here to keep the database system
      // independent of Drupal.
      register_shutdown_function(array($this, 'nextIdDelete'));
      $shutdownRegistered = TRUE;
    }
    return $new_id;
  }

  public function nextIdDelete() {
    // While we want to clean up the table to keep it up from occupying too
    // much storage and memory, we must keep the highest value in the table
    // because InnoDB  uses an in-memory auto-increment counter as long as the
    // server runs. When the server is stopped and restarted, InnoDB
    // reinitializes the counter for each table for the first INSERT to the
    // table based solely on values from the table so deleting all values would
    // be a problem in this case. Also, TRUNCATE resets the auto increment
    // counter.
    try {
      $max_id = $this->query('SELECT MAX(value) FROM {sequences}')->fetchField();
      // We know we are using MySQL here, no need for the slower db_delete().
      $this->query('DELETE FROM {sequences} WHERE value < :value', array(':value' => $max_id));
    }
    // During testing, this function is called from shutdown with the
    // simpletest prefix stored in $this->connection, and those tables are gone
    // by the time shutdown is called so we need to ignore the database
    // errors. There is no problem with completely ignoring errors here: if
    // these queries fail, the sequence will work just fine, just use a bit
    // more database storage and memory.
    catch (PDOException $e) {
    }
  }

  /**
   * Overridden to work around issues to MySQL not supporting transactional DDL.
   */
  protected function popCommittableTransactions() {
    // Commit all the committable layers.
    foreach (array_reverse($this->transactionLayers) as $name => $active) {
      // Stop once we found an active transaction.
      if ($active) {
        break;
      }

      // If there are no more layers left then we should commit.
      unset($this->transactionLayers[$name]);
      if (empty($this->transactionLayers)) {
        if (!PDO::commit()) {
          throw new DatabaseTransactionCommitFailedException();
        }
      }
      else {
        // Attempt to release this savepoint in the standard way.
        try {
          $this->query('RELEASE SAVEPOINT ' . $name);
        }
        catch (PDOException $e) {
          // However, in MySQL (InnoDB), savepoints are automatically committed
          // when tables are altered or created (DDL transactions are not
          // supported). This can cause exceptions due to trying to release
          // savepoints which no longer exist.
          //
          // To avoid exceptions when no actual error has occurred, we silently
          // succeed for MySQL error code 1305 ("SAVEPOINT does not exist").
          if ($e->errorInfo[1] == '1305') {
            // If one SAVEPOINT was released automatically, then all were.
            // Therefore, we keep just the topmost transaction.
            $this->transactionLayers = array('drupal_transaction' => 'drupal_transaction');
          }
          else {
            throw $e;
          }
        }
      }
    }
  }
}


/**
 * @} End of "ingroup database".
 */
