<?php

/**
 * @file
 * Drupal database update API.
 *
 * This file contains functions to perform database updates for a Drupal
 * installation. It is included and used extensively by update.php.
 */

/**
 * Minimum schema version of Drupal 6 required for upgrade to Drupal 7.
 *
 * Upgrades from Drupal 6 to Drupal 7 require that Drupal 6 be running
 * the most recent version, or the upgrade could fail. We can't easily
 * check the Drupal 6 version once the update process has begun, so instead
 * we check the schema version of system.module in the system table.
 */
define('REQUIRED_D6_SCHEMA_VERSION', '6055');

/**
 * Disable any items in the {system} table that are not core compatible.
 */
function update_fix_compatibility() {
  $incompatible = array();
  $result = db_query("SELECT name, type, status FROM {system} WHERE status = 1 AND type IN ('module','theme')");
  foreach ($result as $row) {
    if (update_check_incompatibility($row->name, $row->type)) {
      $incompatible[] = $row->name;
    }
  }
  if (!empty($incompatible)) {
    db_update('system')
      ->fields(array('status' => 0))
      ->condition('name', $incompatible, 'IN')
      ->execute();
  }
}

/**
 * Tests the compatibility of a module or theme.
 */
function update_check_incompatibility($name, $type = 'module') {
  static $themes, $modules;

  // Store values of expensive functions for future use.
  if (empty($themes) || empty($modules)) {
    // We need to do a full rebuild here to make sure the database reflects any
    // code changes that were made in the filesystem before the update script
    // was initiated.
    $themes = system_rebuild_theme_data();
    $modules = system_rebuild_module_data();
  }

  if ($type == 'module' && isset($modules[$name])) {
    $file = $modules[$name];
  }
  elseif ($type == 'theme' && isset($themes[$name])) {
    $file = $themes[$name];
  }
  if (!isset($file)
      || !isset($file->info['core'])
      || $file->info['core'] != DRUPAL_CORE_COMPATIBILITY
      || version_compare(phpversion(), $file->info['php']) < 0) {
    return TRUE;
  }
  return FALSE;
}

/**
 * Performs extra steps required to bootstrap when using a Drupal 6 database.
 *
 * Users who still have a Drupal 6 database (and are in the process of
 * updating to Drupal 7) need extra help before a full bootstrap can be
 * achieved. This function does the necessary preliminary work that allows
 * the bootstrap to be successful.
 *
 * No access check has been performed when this function is called, so no
 * irreversible changes to the database are made here.
 */
function update_prepare_d7_bootstrap() {
  // Allow the bootstrap to proceed even if a Drupal 6 settings.php file is
  // still being used.
  include_once DRUPAL_ROOT . '/includes/install.inc';
  drupal_bootstrap(DRUPAL_BOOTSTRAP_CONFIGURATION);
  global $databases, $db_url, $db_prefix, $update_rewrite_settings;
  if (empty($databases) && !empty($db_url)) {
    $databases = update_parse_db_url($db_url, $db_prefix);
    // Record the fact that the settings.php file will need to be rewritten.
    $update_rewrite_settings = TRUE;
    $settings_file = conf_path() . '/settings.php';
    $writable = drupal_verify_install_file($settings_file, FILE_EXIST|FILE_READABLE|FILE_WRITABLE);
    $requirements = array(
      'settings file' => array(
        'title' => 'Settings file',
        'value' => $writable ? 'The settings file is writable.' : 'The settings file is not writable.',
        'severity' => $writable ? REQUIREMENT_OK : REQUIREMENT_ERROR,
        'description' => $writable ? '' : 'Drupal requires write permissions to <em>' . $settings_file . '</em> during the update process. If you are unsure how to grant file permissions, consult the <a href="http://drupal.org/server-permissions">online handbook</a>.',
      ),
    );
    update_extra_requirements($requirements);
  }

  // The new {blocked_ips} table is used in Drupal 7 to store a list of
  // banned IP addresses. If this table doesn't exist then we are still
  // running on a Drupal 6 database, so we suppress the unavoidable errors
  // that occur by creating a static list.
  $GLOBALS['conf']['blocked_ips'] = array();

  // Check that PDO is available and that the correct PDO database driver is
  // loaded. Bootstrapping to DRUPAL_BOOTSTRAP_DATABASE will result in a fatal
  // error otherwise.
  $message = '';
  $pdo_link = 'http://drupal.org/requirements/pdo';
  // Check that PDO is loaded.
  if (!extension_loaded('pdo')) {
    $message = '<h2>PDO is required!</h2><p>Drupal 7 requires PHP ' . DRUPAL_MINIMUM_PHP . ' or higher with the PHP Data Objects (PDO) extension enabled.</p>';
  }
  // The PDO::ATTR_DEFAULT_FETCH_MODE constant is not available in the PECL
  // version of PDO.
  elseif (!defined('PDO::ATTR_DEFAULT_FETCH_MODE')) {
    $message = '<h2>The wrong version of PDO is installed!</h2><p>Drupal 7 requires the PHP Data Objects (PDO) extension from PHP core to be enabled. This system has the older PECL version installed.';
    $pdo_link = 'http://drupal.org/requirements/pdo#pecl';
  }
  // Check that the correct driver is loaded for the database being updated.
  // If we have no driver information (for example, if someone tried to create
  // the Drupal 7 $databases array themselves but did not do it correctly),
  // this message will be confusing, so do not perform the check; instead, just
  // let the database connection fail in the code that follows.
  elseif (isset($databases['default']['default']['driver']) && !in_array($databases['default']['default']['driver'], PDO::getAvailableDrivers())) {
    $message = '<h2>A PDO database driver is required!</h2><p>You need to enable the PDO_' . strtoupper($databases['default']['default']['driver']) . ' database driver for PHP ' . DRUPAL_MINIMUM_PHP . ' or higher so that Drupal 7 can access the database.</p>';
  }
  if ($message) {
    print $message . '<p>See the <a href="' . $pdo_link . '">system requirements page</a> for more information.</p>';
    exit();
  }

  // Allow the database system to work even if the registry has not been
  // created yet.
  drupal_bootstrap(DRUPAL_BOOTSTRAP_DATABASE);

  // If the site has not updated to Drupal 7 yet, check to make sure that it is
  // running an up-to-date version of Drupal 6 before proceeding. Note this has
  // to happen AFTER the database bootstraps because of
  // drupal_get_installed_schema_version().
  $system_schema = drupal_get_installed_schema_version('system');
  if ($system_schema < 7000) {
    $has_required_schema = $system_schema >= REQUIRED_D6_SCHEMA_VERSION;
    $requirements = array(
      'drupal 6 version' => array(
        'title' => 'Drupal 6 version',
        'value' => $has_required_schema ? 'You are running a current version of Drupal 6.' : 'You are not running a current version of Drupal 6',
        'severity' => $has_required_schema ? REQUIREMENT_OK : REQUIREMENT_ERROR,
        'description' => $has_required_schema ? '' : 'Please update your Drupal 6 installation to the most recent version before attempting to upgrade to Drupal 7',
      ),
    );

    // Make sure that the database environment is properly set up.
    try {
      db_run_tasks(db_driver());
    }
    catch (DatabaseTaskException $e) {
      $requirements['database tasks'] = array(
        'title' => 'Database environment',
        'value' => 'There is a problem with your database environment',
        'severity' => REQUIREMENT_ERROR,
        'description' => $e->getMessage(),
      );
    }

    update_extra_requirements($requirements);

    // Allow a D6 session to work, since the upgrade has not been performed yet.
    $d6_session_name = update_get_d6_session_name();
    if (!empty($_COOKIE[$d6_session_name])) {
      // Set the current sid to the one found in the D6 cookie.
      $sid = $_COOKIE[$d6_session_name];
      $_COOKIE[session_name()] = $sid;
      session_id($sid);
    }

    // Upgrading from D6 to D7.{0,1,2,3,4,8,...} is different than upgrading
    // from D6 to D7.{5,6,7} which should be considered broken. To be able to
    // properly handle this difference in node_update_7012 we need to keep track
    // of whether a D6 > D7 upgrade or a D7 > D7 update is running.
    // Since variable_set() is not available here, the D6 status is being saved
    // in a local variable to be able to store it later.
    $update_d6 = TRUE;
  }

  // Create the registry tables.
  if (!db_table_exists('registry')) {
    $schema['registry'] = array(
      'fields' => array(
        'name'   => array('type' => 'varchar', 'length' => 255, 'not null' => TRUE, 'default' => ''),
        'type'   => array('type' => 'varchar', 'length' => 9, 'not null' => TRUE, 'default' => ''),
        'filename'   => array('type' => 'varchar', 'length' => 255, 'not null' => TRUE, 'default' => ''),
        'module'   => array('type' => 'varchar', 'length' => 255, 'not null' => TRUE, 'default' => ''),
        'weight'   => array('type' => 'int', 'not null' => TRUE, 'default' => 0),
      ),
      'primary key' => array('name', 'type'),
      'indexes' => array(
        'hook' => array('type', 'weight', 'module'),
      ),
    );
    db_create_table('registry', $schema['registry']);
  }
  if (!db_table_exists('registry_file')) {
    $schema['registry_file'] = array(
      'fields' => array(
        'filename'   => array('type' => 'varchar', 'length' => 255, 'not null' => TRUE),
        'hash'   => array('type' => 'varchar', 'length' => 64, 'not null' => TRUE),
      ),
      'primary key' => array('filename'),
    );
    db_create_table('registry_file', $schema['registry_file']);
  }

  // Older versions of Drupal 6 do not include the semaphore table, which is
  // required to bootstrap, so we add it now so that we can bootstrap and
  // provide a reasonable error message.
  if (!db_table_exists('semaphore')) {
    $semaphore = array(
      'description' => 'Table for holding semaphores, locks, flags, etc. that cannot be stored as Drupal variables since they must not be cached.',
      'fields' => array(
        'name' => array(
          'description' => 'Primary Key: Unique name.',
          'type' => 'varchar',
          'length' => 255,
          'not null' => TRUE,
          'default' => ''
        ),
        'value' => array(
          'description' => 'A value for the semaphore.',
          'type' => 'varchar',
          'length' => 255,
          'not null' => TRUE,
          'default' => ''
        ),
        'expire' => array(
          'description' => 'A Unix timestamp with microseconds indicating when the semaphore should expire.',
          'type' => 'float',
          'size' => 'big',
          'not null' => TRUE
        ),
      ),
      'indexes' => array(
        'value' => array('value'),
        'expire' => array('expire'),
      ),
      'primary key' => array('name'),
    );
    db_create_table('semaphore', $semaphore);
  }

  // The new cache_bootstrap bin is required to bootstrap to
  // DRUPAL_BOOTSTRAP_SESSION, so create it here rather than in
  // update_fix_d7_requirements().
  if (!db_table_exists('cache_bootstrap')) {
    $cache_bootstrap = array(
      'description' => 'Cache table for data required to bootstrap Drupal, may be routed to a shared memory cache.',
      'fields' => array(
        'cid' => array(
          'description' => 'Primary Key: Unique cache ID.',
          'type' => 'varchar',
          'length' => 255,
          'not null' => TRUE,
          'default' => '',
        ),
        'data' => array(
          'description' => 'A collection of data to cache.',
          'type' => 'blob',
          'not null' => FALSE,
          'size' => 'big',
        ),
        'expire' => array(
          'description' => 'A Unix timestamp indicating when the cache entry should expire, or 0 for never.',
          'type' => 'int',
          'not null' => TRUE,
          'default' => 0,
        ),
        'created' => array(
          'description' => 'A Unix timestamp indicating when the cache entry was created.',
          'type' => 'int',
          'not null' => TRUE,
          'default' => 0,
        ),
        'serialized' => array(
          'description' => 'A flag to indicate whether content is serialized (1) or not (0).',
          'type' => 'int',
          'size' => 'small',
          'not null' => TRUE,
          'default' => 0,
        ),
      ),
      'indexes' => array(
        'expire' => array('expire'),
      ),
      'primary key' => array('cid'),
    );
    db_create_table('cache_bootstrap', $cache_bootstrap);
  }

  // Set a valid timezone for 6 -> 7 upgrade process.
  drupal_bootstrap(DRUPAL_BOOTSTRAP_VARIABLES);
  $timezone_offset = variable_get('date_default_timezone', 0);
  if (is_numeric($timezone_offset)) {
    // Save the original offset.
    variable_set('date_temporary_timezone', $timezone_offset);
    // Set the timezone for this request only.
    $GLOBALS['conf']['date_default_timezone'] = 'UTC';
  }

  // This allows update functions to tell if an upgrade from D6 is running.
  if (!empty($update_d6)) {
    variable_set('update_d6', TRUE);
  }
}

/**
 * A helper function that modules can use to assist with the transformation
 * from numeric block deltas to string block deltas during the 6.x -> 7.x
 * upgrade.
 *
 * @todo This function should be removed in 8.x.
 *
 * @param $sandbox
 *   An array holding data for the batch process.
 * @param $renamed_deltas
 *   An associative array.  Keys are module names, values an associative array
 *   mapping the old block deltas to the new block deltas for the module.
 *   Example:
 *   @code
 *     $renamed_deltas = array(
 *       'mymodule' =>
 *         array(
 *           0 => 'mymodule-block-1',
 *           1 => 'mymodule-block-2',
 *         ),
 *     );
 *   @endcode
 * @param $moved_deltas
 *   An associative array. Keys are source module names, values an associative
 *   array mapping the (possibly renamed) block name to the new module name.
 *   Example:
 *   @code
 *     $moved_deltas = array(
 *       'user' =>
 *         array(
 *           'navigation' => 'system',
 *         ),
 *     );
 *   @endcode
 */
function update_fix_d7_block_deltas(&$sandbox, $renamed_deltas, $moved_deltas) {
  // Loop through each block and make changes to the block tables.
  // Only run this the first time through the batch update.
  if (!isset($sandbox['progress'])) {
    // Determine whether to use the old or new block table names.
    $block_tables = db_table_exists('blocks') ? array('blocks', 'blocks_roles') : array('block', 'block_role');
    foreach ($block_tables as $table) {
      foreach ($renamed_deltas as $module => $deltas) {
        foreach ($deltas as $old_delta => $new_delta) {
          // Only do the update if the old block actually exists.
          $block_exists = db_query("SELECT COUNT(*) FROM {" . $table . "} WHERE module = :module AND delta = :delta", array(
              ':module' => $module,
              ':delta' => $old_delta,
            ))
            ->fetchField();
          if ($block_exists) {
            // Delete any existing blocks with the new module+delta.
            db_delete($table)
              ->condition('module', $module)
              ->condition('delta', $new_delta)
              ->execute();
            // Rename the old block to the new module+delta.
            db_update($table)
              ->fields(array('delta' => $new_delta))
              ->condition('module', $module)
              ->condition('delta', $old_delta)
              ->execute();
          }
        }
      }
      foreach ($moved_deltas as $old_module => $deltas) {
        foreach ($deltas as $delta => $new_module) {
          // Only do the update if the old block actually exists.
          $block_exists = db_query("SELECT COUNT(*) FROM {" . $table . "} WHERE module = :module AND delta = :delta", array(
              ':module' => $old_module,
              ':delta' => $delta,
            ))
            ->fetchField();
          if ($block_exists) {
            // Delete any existing blocks with the new module+delta.
            db_delete($table)
              ->condition('module', $new_module)
              ->condition('delta', $delta)
              ->execute();
            // Rename the old block to the new module+delta.
            db_update($table)
              ->fields(array('module' => $new_module))
              ->condition('module', $old_module)
              ->condition('delta', $delta)
              ->execute();
          }
        }
      }
    }

    // Initialize batch update information.
    $sandbox['progress'] = 0;
    $sandbox['last_user_processed'] = -1;
    $sandbox['max'] = db_query("SELECT COUNT(*) FROM {users} WHERE data LIKE :block", array(
        ':block' => '%' . db_like(serialize('block')) . '%',
      ))
      ->fetchField();
  }
  // Now do the batch update of the user-specific block visibility settings.
  $limit = 100;
  $result = db_select('users', 'u')
    ->fields('u', array('uid', 'data'))
    ->condition('uid', $sandbox['last_user_processed'], '>')
    ->condition('data', '%' . db_like(serialize('block')) . '%', 'LIKE')
    ->orderBy('uid', 'ASC')
    ->range(0, $limit)
    ->execute();
  foreach ($result as $row) {
    $data = unserialize($row->data);
    $user_needs_update = FALSE;
    foreach ($renamed_deltas as $module => $deltas) {
      foreach ($deltas as $old_delta => $new_delta) {
        if (isset($data['block'][$module][$old_delta])) {
          // Transfer the old block visibility settings to the newly-renamed
          // block, and mark this user for a database update.
          $data['block'][$module][$new_delta] = $data['block'][$module][$old_delta];
          unset($data['block'][$module][$old_delta]);
          $user_needs_update = TRUE;
        }
      }
    }
    foreach ($moved_deltas as $old_module => $deltas) {
      foreach ($deltas as $delta => $new_module) {
        if (isset($data['block'][$old_module][$delta])) {
          // Transfer the old block visibility settings to the moved
          // block, and mark this user for a database update.
          $data['block'][$new_module][$delta] = $data['block'][$old_module][$delta];
          unset($data['block'][$old_module][$delta]);
          $user_needs_update = TRUE;
        }
      }
    }
    // Update the current user.
    if ($user_needs_update) {
      db_update('users')
        ->fields(array('data' => serialize($data)))
        ->condition('uid', $row->uid)
        ->execute();
    }
    // Update our progress information for the batch update.
    $sandbox['progress']++;
    $sandbox['last_user_processed'] = $row->uid;
  }
  // Indicate our current progress to the batch update system.
  if ($sandbox['progress'] < $sandbox['max']) {
    $sandbox['#finished'] = $sandbox['progress'] / $sandbox['max'];
  }
}

/**
 * Perform Drupal 6.x to 7.x updates that are required for update.php
 * to function properly.
 *
 * This function runs when update.php is run the first time for 7.x,
 * even before updates are selected or performed. It is important
 * that if updates are not ultimately performed that no changes are
 * made which make it impossible to continue using the prior version.
 */
function update_fix_d7_requirements() {
  global $conf;

  // Rewrite the settings.php file if necessary, see
  // update_prepare_d7_bootstrap().
  global $update_rewrite_settings, $db_url, $db_prefix;
  if (!empty($update_rewrite_settings)) {
    $databases = update_parse_db_url($db_url, $db_prefix);
    $salt = drupal_hash_base64(drupal_random_bytes(55));
    file_put_contents(conf_path() . '/settings.php', "\n" . '$databases = ' . var_export($databases, TRUE) . ";\n\$drupal_hash_salt = '$salt';", FILE_APPEND);
  }
  if (drupal_get_installed_schema_version('system') < 7000 && !variable_get('update_d7_requirements', FALSE)) {
    // Change 6.x system table field values to 7.x equivalent.
    // Change field values.
    db_change_field('system', 'schema_version', 'schema_version', array(
     'type' => 'int',
     'size' => 'small',
     'not null' => TRUE,
     'default' => -1)
    );
    db_change_field('system', 'status', 'status', array(
      'type' => 'int', 'not null' => TRUE, 'default' => 0));
    db_change_field('system', 'weight', 'weight', array(
      'type' => 'int', 'not null' => TRUE, 'default' => 0));
    db_change_field('system', 'bootstrap', 'bootstrap', array(
      'type' => 'int', 'not null' => TRUE, 'default' => 0));
    // Drop and recreate 6.x indexes.
    db_drop_index('system', 'bootstrap');
    db_add_index('system', 'bootstrap', array(
      'status', 'bootstrap', array('type', 12), 'weight', 'name'));

    db_drop_index('system' ,'modules');
    db_add_index('system', 'modules', array(array(
      'type', 12), 'status', 'weight', 'name'));

    db_drop_index('system', 'type_name');
    db_add_index('system', 'type_name', array(array('type', 12), 'name'));
    // Add 7.x indexes.
    db_add_index('system', 'system_list', array('weight', 'name'));

    // Add the cache_path table.
    if (db_table_exists('cache_path')) {
      db_drop_table('cache_path');
    }
    require_once('./modules/system/system.install');
    $schema['cache_path'] = system_schema_cache_7054();
    $schema['cache_path']['description'] = 'Cache table used for path alias lookups.';
    db_create_table('cache_path', $schema['cache_path']);

    // system_update_7042() renames columns, but these are needed to bootstrap.
    // Add empty columns for now.
    db_add_field('url_alias', 'source', array('type' => 'varchar', 'length' => 255, 'not null' => TRUE, 'default' => ''));
    db_add_field('url_alias', 'alias', array('type' => 'varchar', 'length' => 255, 'not null' => TRUE, 'default' => ''));

    // Add new columns to {menu_router}.
    db_add_field('menu_router', 'delivery_callback', array('type' => 'varchar', 'length' => 255, 'not null' => TRUE, 'default' => ''));
    db_add_field('menu_router', 'context', array(
      'description' => 'Only for local tasks (tabs) - the context of a local task to control its placement.',
      'type' => 'int',
      'not null' => TRUE,
      'default' => 0,
    ));
    db_drop_index('menu_router', 'tab_parent');
    db_add_index('menu_router', 'tab_parent', array(array('tab_parent', 64), 'weight', 'title'));
    db_add_field('menu_router', 'theme_callback', array('type' => 'varchar', 'length' => 255, 'not null' => TRUE, 'default' => ''));
    db_add_field('menu_router', 'theme_arguments', array('type' => 'varchar', 'length' => 255, 'not null' => TRUE, 'default' => ''));

    // Add the role_permission table.
    $schema['role_permission'] = array(
      'fields' => array(
        'rid' => array(
        'type' => 'int',
        'unsigned' => TRUE,
        'not null' => TRUE,
      ),
      'permission' => array(
        'type' => 'varchar',
        'length' => 128,
        'not null' => TRUE,
        'default' => '',
      ),
    ),
    'primary key' => array('rid', 'permission'),
    'indexes' => array(
      'permission' => array('permission'),
      ),
    );
    db_create_table('role_permission', $schema['role_permission']);

    // Drops and recreates semaphore value index.
    db_drop_index('semaphore', 'value');
    db_add_index('semaphore', 'value', array('value'));

    $schema['date_format_type'] = array(
      'description' => 'Stores configured date format types.',
      'fields' => array(
        'type' => array(
          'description' => 'The date format type, e.g. medium.',
          'type' => 'varchar',
          'length' => 64,
          'not null' => TRUE,
        ),
        'title' => array(
          'description' => 'The human readable name of the format type.',
          'type' => 'varchar',
          'length' => 255,
          'not null' => TRUE,
        ),
        'locked' => array(
          'description' => 'Whether or not this is a system provided format.',
          'type' => 'int',
          'size' => 'tiny',
          'default' => 0,
          'not null' => TRUE,
        ),
      ),
      'primary key' => array('type'),
    );

    $schema['date_formats'] = array(
      'description' => 'Stores configured date formats.',
      'fields' => array(
        'dfid' => array(
          'description' => 'The date format identifier.',
          'type' => 'serial',
          'not null' => TRUE,
          'unsigned' => TRUE,
        ),
        'format' => array(
          'description' => 'The date format string.',
          'type' => 'varchar',
          'length' => 100,
          'not null' => TRUE,
        ),
        'type' => array(
          'description' => 'The date format type, e.g. medium.',
          'type' => 'varchar',
          'length' => 64,
          'not null' => TRUE,
        ),
        'locked' => array(
          'description' => 'Whether or not this format can be modified.',
          'type' => 'int',
          'size' => 'tiny',
          'default' => 0,
          'not null' => TRUE,
        ),
      ),
      'primary key' => array('dfid'),
      'unique keys' => array('formats' => array('format', 'type')),
    );

    $schema['date_format_locale'] = array(
      'description' => 'Stores configured date formats for each locale.',
      'fields' => array(
        'format' => array(
          'description' => 'The date format string.',
          'type' => 'varchar',
          'length' => 100,
          'not null' => TRUE,
        ),
        'type' => array(
          'description' => 'The date format type, e.g. medium.',
          'type' => 'varchar',
          'length' => 64,
          'not null' => TRUE,
        ),
        'language' => array(
          'description' => 'A {languages}.language for this format to be used with.',
          'type' => 'varchar',
          'length' => 12,
          'not null' => TRUE,
        ),
      ),
      'primary key' => array('type', 'language'),
    );

    db_create_table('date_format_type', $schema['date_format_type']);
    // Sites that have the Drupal 6 Date module installed already have the
    // following tables.
    if (db_table_exists('date_formats')) {
      db_rename_table('date_formats', 'd6_date_formats');
    }
    db_create_table('date_formats', $schema['date_formats']);
    if (db_table_exists('date_format_locale')) {
      db_rename_table('date_format_locale', 'd6_date_format_locale');
    }
    db_create_table('date_format_locale', $schema['date_format_locale']);

    // Add the queue table.
    $schema['queue'] = array(
      'description' => 'Stores items in queues.',
      'fields' => array(
        'item_id' => array(
          'type' => 'serial',
          'unsigned' => TRUE,
          'not null' => TRUE,
          'description' => 'Primary Key: Unique item ID.',
        ),
        'name' => array(
          'type' => 'varchar',
          'length' => 255,
          'not null' => TRUE,
          'default' => '',
          'description' => 'The queue name.',
        ),
        'data' => array(
          'type' => 'blob',
          'not null' => FALSE,
          'size' => 'big',
          'serialize' => TRUE,
          'description' => 'The arbitrary data for the item.',
        ),
        'expire' => array(
          'type' => 'int',
          'not null' => TRUE,
          'default' => 0,
          'description' => 'Timestamp when the claim lease expires on the item.',
        ),
        'created' => array(
          'type' => 'int',
          'not null' => TRUE,
          'default' => 0,
          'description' => 'Timestamp when the item was created.',
        ),
      ),
      'primary key' => array('item_id'),
      'indexes' => array(
        'name_created' => array('name', 'created'),
        'expire' => array('expire'),
      ),
    );
    // Check for queue table that may remain from D5 or D6, if found
    //drop it.
    if (db_table_exists('queue')) {
      db_drop_table('queue');
    }

    db_create_table('queue', $schema['queue']);

    // Create the sequences table.
    $schema['sequences'] = array(
      'description' => 'Stores IDs.',
      'fields' => array(
        'value' => array(
          'description' => 'The value of the sequence.',
          'type' => 'serial',
          'unsigned' => TRUE,
          'not null' => TRUE,
        ),
       ),
      'primary key' => array('value'),
    );
    // Check for sequences table that may remain from D5 or D6, if found
    //drop it.
    if (db_table_exists('sequences')) {
      db_drop_table('sequences');
    }
    db_create_table('sequences', $schema['sequences']);
    // Initialize the table with the maximum current increment of the tables
    // that will rely on it for their ids.
    $max_aid = db_query('SELECT MAX(aid) FROM {actions_aid}')->fetchField();
    $max_uid = db_query('SELECT MAX(uid) FROM {users}')->fetchField();
    $max_batch_id = db_query('SELECT MAX(bid) FROM {batch}')->fetchField();
    db_insert('sequences')->fields(array('value' => max($max_aid, $max_uid, $max_batch_id)))->execute();

    // Add column for locale context.
    if (db_table_exists('locales_source')) {
      db_add_field('locales_source', 'context', array('type' => 'varchar', 'length' => 255, 'not null' => TRUE, 'default' => '', 'description' => 'The context this string applies to.'));
    }

    // Rename 'site_offline_message' variable to 'maintenance_mode_message'
    // and 'site_offline' variable to 'maintenance_mode'.
    // Old variable is removed in update for system.module, see
    // system_update_7072().
    if ($message = variable_get('site_offline_message', NULL)) {
      variable_set('maintenance_mode_message', $message);
    }
    // Old variable is removed in update for system.module, see
    // system_update_7069().
    $site_offline = variable_get('site_offline', -1);
    if ($site_offline != -1) {
      variable_set('maintenance_mode', $site_offline);
    }

    // Add ssid column and index.
    db_add_field('sessions', 'ssid', array('description' => "Secure session ID. The value is generated by Drupal's session handlers.", 'type' => 'varchar', 'length' => 128, 'not null' => TRUE, 'default' => ''));
    db_add_index('sessions', 'ssid', array('ssid'));
    // Drop existing primary key.
    db_drop_primary_key('sessions');
    // Add new primary key.
    db_add_primary_key('sessions', array('sid', 'ssid'));

    // Allow longer javascript file names.
    if (db_table_exists('languages')) {
      db_change_field('languages', 'javascript', 'javascript', array('type' => 'varchar', 'length' => 64, 'not null' => TRUE, 'default' => ''));
    }

    // Rename action description to label.
    db_change_field('actions', 'description', 'label', array('type' => 'varchar', 'length' => 255, 'not null' => TRUE, 'default' => '0'));

    variable_set('update_d7_requirements', TRUE);
  }

  update_fix_d7_install_profile();
}

/**
 * Register the currently installed profile in the system table.
 *
 * Installation profiles are now treated as modules by Drupal, and have an
 * upgrade path based on their schema version in the system table.
 *
 * The installation profile will be set to schema_version 0, as it has already
 * been installed. Any other hook_update_N functions provided by the
 * installation profile will be run by update.php.
 */
function update_fix_d7_install_profile() {
  $profile = drupal_get_profile();

  $results = db_select('system', 's')
    ->fields('s', array('name', 'schema_version'))
    ->condition('name', $profile)
    ->condition('type', 'module')
    ->execute()
    ->fetchAll();

  if (empty($results)) {
    $filename = 'profiles/' . $profile . '/' . $profile . '.profile';

    // Read profile info file
    $info = drupal_parse_info_file(dirname($filename) . '/' . $profile . '.info');

    // Merge in defaults.
    $info = $info + array(
      'dependencies' => array(),
      'description' => '',
      'package' => 'Other',
      'version' => NULL,
      'php' => DRUPAL_MINIMUM_PHP,
      'files' => array(),
    );

    $values = array(
      'filename' => $filename,
      'name' => $profile,
      'info' => serialize($info),
      'schema_version' => 0,
      'type' => 'module',
      'status' => 1,
      'owner' => '',
    );

    // Installation profile hooks are always executed last by the module system
    $values['weight'] = 1000;

    // Initializing the system table entry for the installation profile
    db_insert('system')
      ->fields(array_keys($values))
      ->values($values)
      ->execute();

    // Reset the cached schema version.
    drupal_get_installed_schema_version($profile, TRUE);

    // Load the updates again to make sure the installation profile updates
    // are loaded.
    drupal_load_updates();
  }
}

/**
 * Parse pre-Drupal 7 database connection URLs and return D7 compatible array.
 *
 * @return
 *   Drupal 7 DBTNG compatible array of database connection information.
 */
function update_parse_db_url($db_url, $db_prefix) {
  $databases = array();
  if (!is_array($db_url)) {
    $db_url = array('default' => $db_url);
  }
  foreach ($db_url as $database => $url) {
    $url = parse_url($url);
    $databases[$database]['default'] = array(
      // MySQLi uses the mysql driver.
      'driver' => $url['scheme'] == 'mysqli' ? 'mysql' : $url['scheme'],
      // Remove the leading slash to get the database name.
      'database' => substr(urldecode($url['path']), 1),
      'username' => urldecode($url['user']),
      'password' => isset($url['pass']) ? urldecode($url['pass']) : '',
      'host' => urldecode($url['host']),
      'port' => isset($url['port']) ? urldecode($url['port']) : '',
    );
    if (isset($db_prefix)) {
      $databases[$database]['default']['prefix'] = $db_prefix;
    }
  }
  return $databases;
}

/**
 * Constructs a session name compatible with a D6 environment.
 *
 * @return
 *   D6-compatible session name string.
 *
 * @see drupal_settings_initialize()
 */
function update_get_d6_session_name() {
  global $base_url, $cookie_domain;
  $cookie_secure = ini_get('session.cookie_secure');

  // If a custom cookie domain is set in settings.php, that variable forms
  // the basis of the session name. Re-compute the D7 hashing method to find
  // out if $cookie_domain was used as the session name.
  if (($cookie_secure ? 'SSESS' : 'SESS') . substr(hash('sha256', $cookie_domain), 0, 32) == session_name()) {
    $session_name = $cookie_domain;
  }
  else {
    // Otherwise use $base_url as session name, without the protocol
    // to use the same session identifiers across HTTP and HTTPS.
    list( , $session_name) = explode('://', $base_url, 2);
  }

  if ($cookie_secure) {
    $session_name .= 'SSL';
  }

  return 'SESS' . md5($session_name);
}

/**
 * Performs one update and stores the results for display on the results page.
 *
 * If an update function completes successfully, it should return a message
 * as a string indicating success, for example:
 * @code
 * return t('New index added successfully.');
 * @endcode
 *
 * Alternatively, it may return nothing. In that case, no message
 * will be displayed at all.
 *
 * If it fails for whatever reason, it should throw an instance of
 * DrupalUpdateException with an appropriate error message, for example:
 * @code
 * throw new DrupalUpdateException(t('Description of what went wrong'));
 * @endcode
 *
 * If an exception is thrown, the current update and all updates that depend on
 * it will be aborted. The schema version will not be updated in this case, and
 * all the aborted updates will continue to appear on update.php as updates
 * that have not yet been run.
 *
 * If an update function needs to be re-run as part of a batch process, it
 * should accept the $sandbox array by reference as its first parameter
 * and set the #finished property to the percentage completed that it is, as a
 * fraction of 1.
 *
 * @param $module
 *   The module whose update will be run.
 * @param $number
 *   The update number to run.
 * @param $dependency_map
 *   An array whose keys are the names of all update functions that will be
 *   performed during this batch process, and whose values are arrays of other
 *   update functions that each one depends on.
 * @param $context
 *   The batch context array.
 *
 * @see update_resolve_dependencies()
 */
function update_do_one($module, $number, $dependency_map, &$context) {
  $function = $module . '_update_' . $number;

  // If this update was aborted in a previous step, or has a dependency that
  // was aborted in a previous step, go no further.
  if (!empty($context['results']['#abort']) && array_intersect($context['results']['#abort'], array_merge($dependency_map, array($function)))) {
    return;
  }

  $ret = array();
  if (function_exists($function)) {
    try {
      $ret['results']['query'] = $function($context['sandbox']);
      $ret['results']['success'] = TRUE;
    }
    // @TODO We may want to do different error handling for different
    // exception types, but for now we'll just log the exception and
    // return the message for printing.
    catch (Exception $e) {
      watchdog_exception('update', $e);

      require_once DRUPAL_ROOT . '/includes/errors.inc';
      $variables = _drupal_decode_exception($e);
      // The exception message is run through check_plain() by _drupal_decode_exception().
      $ret['#abort'] = array('success' => FALSE, 'query' => t('%type: !message in %function (line %line of %file).', $variables));
    }
  }

  if (isset($context['sandbox']['#finished'])) {
    $context['finished'] = $context['sandbox']['#finished'];
    unset($context['sandbox']['#finished']);
  }

  if (!isset($context['results'][$module])) {
    $context['results'][$module] = array();
  }
  if (!isset($context['results'][$module][$number])) {
    $context['results'][$module][$number] = array();
  }
  $context['results'][$module][$number] = array_merge($context['results'][$module][$number], $ret);

  if (!empty($ret['#abort'])) {
    // Record this function in the list of updates that were aborted.
    $context['results']['#abort'][] = $function;
  }

  // Record the schema update if it was completed successfully.
  if ($context['finished'] == 1 && empty($ret['#abort'])) {
    drupal_set_installed_schema_version($module, $number);
  }

  $context['message'] = 'Updating ' . check_plain($module) . ' module';
}

/**
 * @class Exception class used to throw error if a module update fails.
 */
class DrupalUpdateException extends Exception { }

/**
 * Starts the database update batch process.
 *
 * @param $start
 *   An array whose keys contain the names of modules to be updated during the
 *   current batch process, and whose values contain the number of the first
 *   requested update for that module. The actual updates that are run (and the
 *   order they are run in) will depend on the results of passing this data
 *   through the update dependency system.
 * @param $redirect
 *   Path to redirect to when the batch has finished processing.
 * @param $url
 *   URL of the batch processing page (should only be used for separate
 *   scripts like update.php).
 * @param $batch
 *   Optional parameters to pass into the batch API.
 * @param $redirect_callback
 *   (optional) Specify a function to be called to redirect to the progressive
 *   processing page.
 *
 * @see update_resolve_dependencies()
 */
function update_batch($start, $redirect = NULL, $url = NULL, $batch = array(), $redirect_callback = 'drupal_goto') {
  // During the update, bring the site offline so that schema changes do not
  // affect visiting users.
  $_SESSION['maintenance_mode'] = variable_get('maintenance_mode', FALSE);
  if ($_SESSION['maintenance_mode'] == FALSE) {
    variable_set('maintenance_mode', TRUE);
  }

  // Resolve any update dependencies to determine the actual updates that will
  // be run and the order they will be run in.
  $updates = update_resolve_dependencies($start);

  // Store the dependencies for each update function in an array which the
  // batch API can pass in to the batch operation each time it is called. (We
  // do not store the entire update dependency array here because it is
  // potentially very large.)
  $dependency_map = array();
  foreach ($updates as $function => $update) {
    $dependency_map[$function] = !empty($update['reverse_paths']) ? array_keys($update['reverse_paths']) : array();
  }

  $operations = array();
  foreach ($updates as $update) {
    if ($update['allowed']) {
      // Set the installed version of each module so updates will start at the
      // correct place. (The updates are already sorted, so we can simply base
      // this on the first one we come across in the above foreach loop.)
      if (isset($start[$update['module']])) {
        drupal_set_installed_schema_version($update['module'], $update['number'] - 1);
        unset($start[$update['module']]);
      }
      // Add this update function to the batch.
      $function = $update['module'] . '_update_' . $update['number'];
      $operations[] = array('update_do_one', array($update['module'], $update['number'], $dependency_map[$function]));
    }
  }
  $batch['operations'] = $operations;
  $batch += array(
    'title' => 'Updating',
    'init_message' => 'Starting updates',
    'error_message' => 'An unrecoverable error has occurred. You can find the error message below. It is advised to copy it to the clipboard for reference.',
    'finished' => 'update_finished',
    'file' => 'includes/update.inc',
  );
  batch_set($batch);
  batch_process($redirect, $url, $redirect_callback);
}

/**
 * Finishes the update process and stores the results for eventual display.
 *
 * After the updates run, all caches are flushed. The update results are
 * stored into the session (for example, to be displayed on the update results
 * page in update.php). Additionally, if the site was off-line, now that the
 * update process is completed, the site is set back online.
 *
 * @param $success
 *   Indicate that the batch API tasks were all completed successfully.
 * @param $results
 *   An array of all the results that were updated in update_do_one().
 * @param $operations
 *   A list of all the operations that had not been completed by the batch API.
 *
 * @see update_batch()
 */
function update_finished($success, $results, $operations) {
  // Remove the D6 upgrade flag variable so that subsequent update runs do not
  // get the wrong context.
  variable_del('update_d6');

  // Clear the caches in case the data has been updated.
  drupal_flush_all_caches();

  $_SESSION['update_results'] = $results;
  $_SESSION['update_success'] = $success;
  $_SESSION['updates_remaining'] = $operations;

  // Now that the update is done, we can put the site back online if it was
  // previously in maintenance mode.
  if (isset($_SESSION['maintenance_mode']) && $_SESSION['maintenance_mode'] == FALSE) {
    variable_set('maintenance_mode', FALSE);
    unset($_SESSION['maintenance_mode']);
  }
}

/**
 * Returns a list of all the pending database updates.
 *
 * @return
 *   An associative array keyed by module name which contains all information
 *   about database updates that need to be run, and any updates that are not
 *   going to proceed due to missing requirements. The system module will
 *   always be listed first.
 *
 *   The subarray for each module can contain the following keys:
 *   - start: The starting update that is to be processed. If this does not
 *       exist then do not process any updates for this module as there are
 *       other requirements that need to be resolved.
 *   - warning: Any warnings about why this module can not be updated.
 *   - pending: An array of all the pending updates for the module including
 *       the update number and the description from source code comment for
 *       each update function. This array is keyed by the update number.
 */
function update_get_update_list() {
  // Make sure that the system module is first in the list of updates.
  $ret = array('system' => array());

  $modules = drupal_get_installed_schema_version(NULL, FALSE, TRUE);
  foreach ($modules as $module => $schema_version) {
    // Skip uninstalled and incompatible modules.
    if ($schema_version == SCHEMA_UNINSTALLED || update_check_incompatibility($module)) {
      continue;
    }
    // Otherwise, get the list of updates defined by this module.
    $updates = drupal_get_schema_versions($module);
    if ($updates !== FALSE) {
      // module_invoke returns NULL for nonexisting hooks, so if no updates
      // are removed, it will == 0.
      $last_removed = module_invoke($module, 'update_last_removed');
      if ($schema_version < $last_removed) {
        $ret[$module]['warning'] = '<em>' . $module . '</em> module can not be updated. Its schema version is ' . $schema_version . '. Updates up to and including ' . $last_removed . ' have been removed in this release. In order to update <em>' . $module . '</em> module, you will first <a href="http://drupal.org/upgrade">need to upgrade</a> to the last version in which these updates were available.';
        continue;
      }

      $updates = drupal_map_assoc($updates);
      foreach (array_keys($updates) as $update) {
        if ($update > $schema_version) {
          // The description for an update comes from its Doxygen.
          $func = new ReflectionFunction($module . '_update_' . $update);
          $description = str_replace(array("\n", '*', '/'), '', $func->getDocComment());
          $ret[$module]['pending'][$update] = "$update - $description";
          if (!isset($ret[$module]['start'])) {
            $ret[$module]['start'] = $update;
          }
        }
      }
      if (!isset($ret[$module]['start']) && isset($ret[$module]['pending'])) {
        $ret[$module]['start'] = $schema_version;
      }
    }
  }

  if (empty($ret['system'])) {
    unset($ret['system']);
  }
  return $ret;
}

/**
 * Resolves dependencies in a set of module updates, and orders them correctly.
 *
 * This function receives a list of requested module updates and determines an
 * appropriate order to run them in such that all update dependencies are met.
 * Any updates whose dependencies cannot be met are included in the returned
 * array but have the key 'allowed' set to FALSE; the calling function should
 * take responsibility for ensuring that these updates are ultimately not
 * performed.
 *
 * In addition, the returned array also includes detailed information about the
 * dependency chain for each update, as provided by the depth-first search
 * algorithm in drupal_depth_first_search().
 *
 * @param $starting_updates
 *   An array whose keys contain the names of modules with updates to be run
 *   and whose values contain the number of the first requested update for that
 *   module.
 *
 * @return
 *   An array whose keys are the names of all update functions within the
 *   provided modules that would need to be run in order to fulfill the
 *   request, arranged in the order in which the update functions should be
 *   run. (This includes the provided starting update for each module and all
 *   subsequent updates that are available.) The values are themselves arrays
 *   containing all the keys provided by the drupal_depth_first_search()
 *   algorithm, which encode detailed information about the dependency chain
 *   for this update function (for example: 'paths', 'reverse_paths', 'weight',
 *   and 'component'), as well as the following additional keys:
 *   - 'allowed': A boolean which is TRUE when the update function's
 *     dependencies are met, and FALSE otherwise. Calling functions should
 *     inspect this value before running the update.
 *   - 'missing_dependencies': An array containing the names of any other
 *     update functions that are required by this one but that are unavailable
 *     to be run. This array will be empty when 'allowed' is TRUE.
 *   - 'module': The name of the module that this update function belongs to.
 *   - 'number': The number of this update function within that module.
 *
 * @see drupal_depth_first_search()
 */
function update_resolve_dependencies($starting_updates) {
  // Obtain a dependency graph for the requested update functions.
  $update_functions = update_get_update_function_list($starting_updates);
  $graph = update_build_dependency_graph($update_functions);

  // Perform the depth-first search and sort the results.
  require_once DRUPAL_ROOT . '/includes/graph.inc';
  drupal_depth_first_search($graph);
  uasort($graph, 'drupal_sort_weight');

  foreach ($graph as $function => &$data) {
    $module = $data['module'];
    $number = $data['number'];
    // If the update function is missing and has not yet been performed, mark
    // it and everything that ultimately depends on it as disallowed.
    if (update_is_missing($module, $number, $update_functions) && !update_already_performed($module, $number)) {
      $data['allowed'] = FALSE;
      foreach (array_keys($data['paths']) as $dependent) {
        $graph[$dependent]['allowed'] = FALSE;
        $graph[$dependent]['missing_dependencies'][] = $function;
      }
    }
    elseif (!isset($data['allowed'])) {
      $data['allowed'] = TRUE;
      $data['missing_dependencies'] = array();
    }
    // Now that we have finished processing this function, remove it from the
    // graph if it was not part of the original list. This ensures that we
    // never try to run any updates that were not specifically requested.
    if (!isset($update_functions[$module][$number])) {
      unset($graph[$function]);
    }
  }

  return $graph;
}

/**
 * Returns an organized list of update functions for a set of modules.
 *
 * @param $starting_updates
 *   An array whose keys contain the names of modules and whose values contain
 *   the number of the first requested update for that module.
 *
 * @return
 *   An array containing all the update functions that should be run for each
 *   module, including the provided starting update and all subsequent updates
 *   that are available. The keys of the array contain the module names, and
 *   each value is an ordered array of update functions, keyed by the update
 *   number.
 *
 * @see update_resolve_dependencies()
 */
function update_get_update_function_list($starting_updates) {
  // Go through each module and find all updates that we need (including the
  // first update that was requested and any updates that run after it).
  $update_functions = array();
  foreach ($starting_updates as $module => $version) {
    $update_functions[$module] = array();
    $updates = drupal_get_schema_versions($module);
    if ($updates !== FALSE) {
      $max_version = max($updates);
      if ($version <= $max_version) {
        foreach ($updates as $update) {
          if ($update >= $version) {
            $update_functions[$module][$update] = $module . '_update_' . $update;
          }
        }
      }
    }
  }
  return $update_functions;
}

/**
 * Constructs a graph which encodes the dependencies between module updates.
 *
 * This function returns an associative array which contains a "directed graph"
 * representation of the dependencies between a provided list of update
 * functions, as well as any outside update functions that they directly depend
 * on but that were not in the provided list. The vertices of the graph
 * represent the update functions themselves, and each edge represents a
 * requirement that the first update function needs to run before the second.
 * For example, consider this graph:
 *
 * system_update_7000 ---> system_update_7001 ---> system_update_7002
 *
 * Visually, this indicates that system_update_7000() must run before
 * system_update_7001(), which in turn must run before system_update_7002().
 *
 * The function takes into account standard dependencies within each module, as
 * shown above (i.e., the fact that each module's updates must run in numerical
 * order), but also finds any cross-module dependencies that are defined by
 * modules which implement hook_update_dependencies(), and builds them into the
 * graph as well.
 *
 * @param $update_functions
 *   An organized array of update functions, in the format returned by
 *   update_get_update_function_list().
 *
 * @return
 *   A multidimensional array representing the dependency graph, suitable for
 *   passing in to drupal_depth_first_search(), but with extra information
 *   about each update function also included. Each array key contains the name
 *   of an update function, including all update functions from the provided
 *   list as well as any outside update functions which they directly depend
 *   on. Each value is an associative array containing the following keys:
 *   - 'edges': A representation of any other update functions that immediately
 *     depend on this one. See drupal_depth_first_search() for more details on
 *     the format.
 *   - 'module': The name of the module that this update function belongs to.
 *   - 'number': The number of this update function within that module.
 *
 * @see drupal_depth_first_search()
 * @see update_resolve_dependencies()
 */
function update_build_dependency_graph($update_functions) {
  // Initialize an array that will define a directed graph representing the
  // dependencies between update functions.
  $graph = array();

  // Go through each update function and build an initial list of dependencies.
  foreach ($update_functions as $module => $functions) {
    $previous_function = NULL;
    foreach ($functions as $number => $function) {
      // Add an edge to the directed graph representing the fact that each
      // update function in a given module must run after the update that
      // numerically precedes it.
      if ($previous_function) {
        $graph[$previous_function]['edges'][$function] = TRUE;
      }
      $previous_function = $function;

      // Define the module and update number associated with this function.
      $graph[$function]['module'] = $module;
      $graph[$function]['number'] = $number;
    }
  }

  // Now add any explicit update dependencies declared by modules.
  $update_dependencies = update_retrieve_dependencies();
  foreach ($graph as $function => $data) {
    if (!empty($update_dependencies[$data['module']][$data['number']])) {
      foreach ($update_dependencies[$data['module']][$data['number']] as $module => $number) {
        $dependency = $module . '_update_' . $number;
        $graph[$dependency]['edges'][$function] = TRUE;
        $graph[$dependency]['module'] = $module;
        $graph[$dependency]['number'] = $number;
      }
    }
  }

  return $graph;
}

/**
 * Determines if a module update is missing or unavailable.
 *
 * @param $module
 *   The name of the module.
 * @param $number
 *   The number of the update within that module.
 * @param $update_functions
 *   An organized array of update functions, in the format returned by
 *   update_get_update_function_list(). This should represent all module
 *   updates that are requested to run at the time this function is called.
 *
 * @return
 *   TRUE if the provided module update is not installed or is not in the
 *   provided list of updates to run; FALSE otherwise.
 */
function update_is_missing($module, $number, $update_functions) {
  return !isset($update_functions[$module][$number]) || !function_exists($update_functions[$module][$number]);
}

/**
 * Determines if a module update has already been performed.
 *
 * @param $module
 *   The name of the module.
 * @param $number
 *   The number of the update within that module.
 *
 * @return
 *   TRUE if the database schema indicates that the update has already been
 *   performed; FALSE otherwise.
 */
function update_already_performed($module, $number) {
  return $number <= drupal_get_installed_schema_version($module);
}

/**
 * Invokes hook_update_dependencies() in all installed modules.
 *
 * This function is similar to module_invoke_all(), with the main difference
 * that it does not require that a module be enabled to invoke its hook, only
 * that it be installed. This allows the update system to properly perform
 * updates even on modules that are currently disabled.
 *
 * @return
 *   An array of return values obtained by merging the results of the
 *   hook_update_dependencies() implementations in all installed modules.
 *
 * @see module_invoke_all()
 * @see hook_update_dependencies()
 */
function update_retrieve_dependencies() {
  $return = array();
  // Get a list of installed modules, arranged so that we invoke their hooks in
  // the same order that module_invoke_all() does.
  $modules = db_query("SELECT name FROM {system} WHERE type = 'module' AND schema_version <> :schema ORDER BY weight ASC, name ASC", array(':schema' => SCHEMA_UNINSTALLED))->fetchCol();
  foreach ($modules as $module) {
    $function = $module . '_update_dependencies';
    if (function_exists($function)) {
      $result = $function();
      // Each implementation of hook_update_dependencies() returns a
      // multidimensional, associative array containing some keys that
      // represent module names (which are strings) and other keys that
      // represent update function numbers (which are integers). We cannot use
      // array_merge_recursive() to properly merge these results, since it
      // treats strings and integers differently. Therefore, we have to
      // explicitly loop through the expected array structure here and perform
      // the merge manually.
      if (isset($result) && is_array($result)) {
        foreach ($result as $module => $module_data) {
          foreach ($module_data as $update => $update_data) {
            foreach ($update_data as $module_dependency => $update_dependency) {
              // If there are redundant dependencies declared for the same
              // update function (so that it is declared to depend on more than
              // one update from a particular module), record the dependency on
              // the highest numbered update here, since that automatically
              // implies the previous ones. For example, if one module's
              // implementation of hook_update_dependencies() required this
              // ordering:
              //
              // system_update_7001 ---> user_update_7000
              //
              // but another module's implementation of the hook required this
              // one:
              //
              // system_update_7002 ---> user_update_7000
              //
              // we record the second one, since system_update_7001() is always
              // guaranteed to run before system_update_7002() anyway (within
              // an individual module, updates are always run in numerical
              // order).
              if (!isset($return[$module][$update][$module_dependency]) || $update_dependency > $return[$module][$update][$module_dependency]) {
                $return[$module][$update][$module_dependency] = $update_dependency;
              }
            }
          }
        }
      }
    }
  }

  return $return;
}