class FieldInfo {

  /**
   * Lightweight map of fields across entity types and bundles.
   *
   * @var array
   */
  protected $fieldMap;

  /**
   * List of $field structures keyed by ID. Includes deleted fields.
   *
   * @var array
   */
  protected $fieldsById = array();

  /**
   * Mapping of field names to the ID of the corresponding non-deleted field.
   *
   * @var array
   */
  protected $fieldIdsByName = array();

  /**
   * Whether $fieldsById contains all field definitions or a subset.
   *
   * @var bool
   */
  protected $loadedAllFields = FALSE;

  /**
   * Separately tracks requested field names or IDs that do not exist.
   *
   * @var array
   */
  protected $unknownFields = array();

  /**
   * Instance definitions by bundle.
   *
   * @var array
   */
  protected $bundleInstances = array();

  /**
   * Whether $bundleInstances contains all instances definitions or a subset.
   *
   * @var bool
   */
  protected $loadedAllInstances = FALSE;

  /**
   * Separately tracks requested bundles that are empty (or do not exist).
   *
   * @var array
   */
  protected $emptyBundles = array();

  /**
   * Extra fields by bundle.
   *
   * @var array
   */
  protected $bundleExtraFields = array();

  /**
   * Clears the "static" and persistent caches.
   */
  public function flush() {
    $this->fieldMap = NULL;

    $this->fieldsById = array();
    $this->fieldIdsByName = array();
    $this->loadedAllFields = FALSE;
    $this->unknownFields = array();

    $this->bundleInstances = array();
    $this->loadedAllInstances = FALSE;
    $this->emptyBundles = array();

    $this->bundleExtraFields = array();

    cache_clear_all('field_info:', 'cache_field', TRUE);
  }

  /**
   * Collects a lightweight map of fields across bundles.
   *
   * @return
   *   An array keyed by field name. Each value is an array with two entries:
   *   - type: The field type.
   *   - bundles: The bundles in which the field appears, as an array with
   *     entity types as keys and the array of bundle names as values.
   */
  public function getFieldMap() {
    // Read from the "static" cache.
    if ($this->fieldMap !== NULL) {
      return $this->fieldMap;
    }

    // Read from persistent cache.
    if ($cached = cache_get('field_info:field_map', 'cache_field')) {
      $map = $cached->data;

      // Save in "static" cache.
      $this->fieldMap = $map;

      return $map;
    }

    $map = array();

    $query = db_query('SELECT fc.type, fci.field_name, fci.entity_type, fci.bundle FROM {field_config_instance} fci INNER JOIN {field_config} fc ON fc.id = fci.field_id WHERE fc.active = 1 AND fc.storage_active = 1 AND fc.deleted = 0 AND fci.deleted = 0');
    foreach ($query as $row) {
      $map[$row->field_name]['bundles'][$row->entity_type][] = $row->bundle;
      $map[$row->field_name]['type'] = $row->type;
    }

    // Save in "static" and persistent caches.
    $this->fieldMap = $map;
    cache_set('field_info:field_map', $map, 'cache_field');

    return $map;
  }

  /**
   * Returns all active fields, including deleted ones.
   *
   * @return
   *   An array of field definitions, keyed by field ID.
   */
  public function getFields() {
    // Read from the "static" cache.
    if ($this->loadedAllFields) {
      return $this->fieldsById;
    }

    // Read from persistent cache.
    if ($cached = cache_get('field_info:fields', 'cache_field')) {
      $this->fieldsById = $cached->data;
    }
    else {
      // Collect and prepare fields.
      foreach (field_read_fields(array(), array('include_deleted' => TRUE)) as $field) {
        $this->fieldsById[$field['id']] = $this->prepareField($field);
      }

      // Store in persistent cache.
      cache_set('field_info:fields', $this->fieldsById, 'cache_field');
    }

    // Fill the name/ID map.
    foreach ($this->fieldsById as $field) {
      if (!$field['deleted']) {
        $this->fieldIdsByName[$field['field_name']] = $field['id'];
      }
    }

    $this->loadedAllFields = TRUE;

    return $this->fieldsById;
  }

  /**
   * Retrieves all active, non-deleted instances definitions.
   *
   * @param $entity_type
   *   (optional) The entity type.
   *
   * @return
   *   If $entity_type is not set, all instances keyed by entity type and bundle
   *   name. If $entity_type is set, all instances for that entity type, keyed
   *   by bundle name.
   */
  public function getInstances($entity_type = NULL) {
    // If the full list is not present in "static" cache yet.
    if (!$this->loadedAllInstances) {

      // Read from persistent cache.
      if ($cached = cache_get('field_info:instances', 'cache_field')) {
        $this->bundleInstances = $cached->data;
      }
      else {
        // Collect and prepare instances.

        // We also need to populate the static field cache, since it will not
        // be set by subsequent getBundleInstances() calls.
        $this->getFields();

        // Initialize empty arrays for all existing entity types and bundles.
        // This is not strictly needed, but is done to preserve the behavior of
        // field_info_instances() before http://drupal.org/node/1915646.
        foreach (field_info_bundles() as $existing_entity_type => $bundles) {
          foreach ($bundles as $bundle => $bundle_info) {
            $this->bundleInstances[$existing_entity_type][$bundle] = array();
          }
        }

        foreach (field_read_instances() as $instance) {
          $field = $this->getField($instance['field_name']);
          $instance = $this->prepareInstance($instance, $field['type']);
          $this->bundleInstances[$instance['entity_type']][$instance['bundle']][$instance['field_name']] = $instance;
        }

        // Store in persistent cache.
        cache_set('field_info:instances', $this->bundleInstances, 'cache_field');
      }

      $this->loadedAllInstances = TRUE;
    }

    if (isset($entity_type)) {
      return isset($this->bundleInstances[$entity_type]) ? $this->bundleInstances[$entity_type] : array();
    }
    else {
      return $this->bundleInstances;
    }
  }

  /**
   * Returns a field definition from a field name.
   *
   * This method only retrieves active, non-deleted fields.
   *
   * @param $field_name
   *   The field name.
   *
   * @return
   *   The field definition, or NULL if no field was found.
   */
  public function getField($field_name) {
    // Read from the "static" cache.
    if (isset($this->fieldIdsByName[$field_name])) {
      $field_id = $this->fieldIdsByName[$field_name];
      return $this->fieldsById[$field_id];
    }
    if (isset($this->unknownFields[$field_name])) {
      return;
    }

    // Do not check the (large) persistent cache, but read the definition.

    // Cache miss: read from definition.
    if ($field = field_read_field($field_name)) {
      $field = $this->prepareField($field);

      // Save in the "static" cache.
      $this->fieldsById[$field['id']] = $field;
      $this->fieldIdsByName[$field['field_name']] = $field['id'];

      return $field;
    }
    else {
      $this->unknownFields[$field_name] = TRUE;
    }
  }

  /**
   * Returns a field definition from a field ID.
   *
   * This method only retrieves active fields, deleted or not.
   *
   * @param $field_id
   *   The field ID.
   *
   * @return
   *   The field definition, or NULL if no field was found.
   */
  public function getFieldById($field_id) {
    // Read from the "static" cache.
    if (isset($this->fieldsById[$field_id])) {
      return $this->fieldsById[$field_id];
    }
    if (isset($this->unknownFields[$field_id])) {
      return;
    }

    // No persistent cache, fields are only persistently cached as part of a
    // bundle.

    // Cache miss: read from definition.
    if ($fields = field_read_fields(array('id' => $field_id), array('include_deleted' => TRUE))) {
      $field = current($fields);
      $field = $this->prepareField($field);

      // Store in the static cache.
      $this->fieldsById[$field['id']] = $field;
      if (!$field['deleted']) {
        $this->fieldIdsByName[$field['field_name']] = $field['id'];
      }

      return $field;
    }
    else {
      $this->unknownFields[$field_id] = TRUE;
    }
  }

  /**
   * Retrieves the instances for a bundle.
   *
   * The function also populates the corresponding field definitions in the
   * "static" cache.
   *
   * @param $entity_type
   *   The entity type.
   * @param $bundle
   *   The bundle name.
   *
   * @return
   *   The array of instance definitions, keyed by field name.
   */
  public function getBundleInstances($entity_type, $bundle) {
    // Read from the "static" cache.
    if (isset($this->bundleInstances[$entity_type][$bundle])) {
      return $this->bundleInstances[$entity_type][$bundle];
    }
    if (isset($this->emptyBundles[$entity_type][$bundle])) {
      return array();
    }

    // Read from the persistent cache.
    if ($cached = cache_get("field_info:bundle:$entity_type:$bundle", 'cache_field')) {
      $info = $cached->data;

      // Extract the field definitions and save them in the "static" cache.
      foreach ($info['fields'] as $field) {
        if (!isset($this->fieldsById[$field['id']])) {
          $this->fieldsById[$field['id']] = $field;
          if (!$field['deleted']) {
            $this->fieldIdsByName[$field['field_name']] = $field['id'];
          }
        }
      }
      unset($info['fields']);

      // Store the instance definitions in the "static" cache'. Empty (or
      // non-existent) bundles are stored separately, so that they do not
      // pollute the global list returned by getInstances().
      if ($info['instances']) {
        $this->bundleInstances[$entity_type][$bundle] = $info['instances'];
      }
      else {
        $this->emptyBundles[$entity_type][$bundle] = TRUE;
      }

      return $info['instances'];
    }

    // Cache miss: collect from the definitions.

    $instances = array();

    // Collect the fields in the bundle.
    $params = array('entity_type' => $entity_type, 'bundle' => $bundle);
    $fields = field_read_fields($params);

    // This iterates on non-deleted instances, so deleted fields are kept out of
    // the persistent caches.
    foreach (field_read_instances($params) as $instance) {
      $field = $fields[$instance['field_name']];

      $instance = $this->prepareInstance($instance, $field['type']);
      $instances[$field['field_name']] = $instance;

      // If the field is not in our global "static" list yet, add it.
      if (!isset($this->fieldsById[$field['id']])) {
        $field = $this->prepareField($field);

        $this->fieldsById[$field['id']] = $field;
        $this->fieldIdsByName[$field['field_name']] = $field['id'];
      }
    }

    // Store in the 'static' cache'. Empty (or non-existent) bundles are stored
    // separately, so that they do not pollute the global list returned by
    // getInstances().
    if ($instances) {
      $this->bundleInstances[$entity_type][$bundle] = $instances;
    }
    else {
      $this->emptyBundles[$entity_type][$bundle] = TRUE;
    }

    // The persistent cache additionally contains the definitions of the fields
    // involved in the bundle.
    $cache = array(
      'instances' => $instances,
      'fields' => array()
    );
    foreach ($instances as $instance) {
      $cache['fields'][] = $this->fieldsById[$instance['field_id']];
    }
    cache_set("field_info:bundle:$entity_type:$bundle", $cache, 'cache_field');

    return $instances;
  }

  /**
   * Retrieves the "extra fields" for a bundle.
   *
   * @param $entity_type
   *   The entity type.
   * @param $bundle
   *   The bundle name.
   *
   * @return
   *   The array of extra fields.
   */
  public function getBundleExtraFields($entity_type, $bundle) {
    // Read from the "static" cache.
    if (isset($this->bundleExtraFields[$entity_type][$bundle])) {
      return $this->bundleExtraFields[$entity_type][$bundle];
    }

    // Read from the persistent cache.
    if ($cached = cache_get("field_info:bundle_extra:$entity_type:$bundle", 'cache_field')) {
      $this->bundleExtraFields[$entity_type][$bundle] = $cached->data;
      return $this->bundleExtraFields[$entity_type][$bundle];
    }

    // Cache miss: read from hook_field_extra_fields(). Note: given the current
    // shape of the hook, we have no other way than collecting extra fields on
    // all bundles.
    $info = array();
    $extra = module_invoke_all('field_extra_fields');
    drupal_alter('field_extra_fields', $extra);
    // Merge in saved settings.
    if (isset($extra[$entity_type][$bundle])) {
      $info = $this->prepareExtraFields($extra[$entity_type][$bundle], $entity_type, $bundle);
    }

    // Store in the 'static' and persistent caches.
    $this->bundleExtraFields[$entity_type][$bundle] = $info;
    cache_set("field_info:bundle_extra:$entity_type:$bundle", $info, 'cache_field');

    return $this->bundleExtraFields[$entity_type][$bundle];
  }

  /**
   * Prepares a field definition for the current run-time context.
   *
   * @param $field
   *   The raw field structure as read from the database.
   *
   * @return
   *   The field definition completed for the current runtime context.
   */
  public function prepareField($field) {
    // Make sure all expected field settings are present.
    $field['settings'] += field_info_field_settings($field['type']);
    $field['storage']['settings'] += field_info_storage_settings($field['storage']['type']);

    // Add storage details.
    $details = (array) module_invoke($field['storage']['module'], 'field_storage_details', $field);
    drupal_alter('field_storage_details', $details, $field);
    $field['storage']['details'] = $details;

    // Populate the list of bundles using the field.
    $field['bundles'] = array();
    if (!$field['deleted']) {
      $map = $this->getFieldMap();
      if (isset($map[$field['field_name']])) {
        $field['bundles'] = $map[$field['field_name']]['bundles'];
      }
    }

    return $field;
  }

  /**
   * Prepares an instance definition for the current run-time context.
   *
   * @param $instance
   *   The raw instance structure as read from the database.
   * @param $field_type
   *   The field type.
   *
   * @return
   *   The field instance array completed for the current runtime context.
   */
  public function prepareInstance($instance, $field_type) {
    // Make sure all expected instance settings are present.
    $instance['settings'] += field_info_instance_settings($field_type);

    // Set a default value for the instance.
    if (field_behaviors_widget('default value', $instance) == FIELD_BEHAVIOR_DEFAULT && !isset($instance['default_value'])) {
      $instance['default_value'] = NULL;
    }

    // Prepare widget settings.
    $instance['widget'] = $this->prepareInstanceWidget($instance['widget'], $field_type);

    // Prepare display settings.
    foreach ($instance['display'] as $view_mode => $display) {
      $instance['display'][$view_mode] = $this->prepareInstanceDisplay($display, $field_type);
    }

    // Fall back to 'hidden' for view modes configured to use custom display
    // settings, and for which the instance has no explicit settings.
    $entity_info = entity_get_info($instance['entity_type']);
    $view_modes = array_merge(array('default'), array_keys($entity_info['view modes']));
    $view_mode_settings = field_view_mode_settings($instance['entity_type'], $instance['bundle']);
    foreach ($view_modes as $view_mode) {
      if ($view_mode == 'default' || !empty($view_mode_settings[$view_mode]['custom_settings'])) {
        if (!isset($instance['display'][$view_mode])) {
          $instance['display'][$view_mode] = array(
            'type' => 'hidden',
            'label' => 'above',
            'settings' => array(),
            'weight' => 0,
          );
        }
      }
    }

    return $instance;
  }

  /**
   * Prepares widget properties for the current run-time context.
   *
   * @param $widget
   *   Widget specifications as found in $instance['widget'].
   * @param $field_type
   *   The field type.
   *
   * @return
   *   The widget properties completed for the current runtime context.
   */
  public function prepareInstanceWidget($widget, $field_type) {
    $field_type_info = field_info_field_types($field_type);

    // Fill in default values.
    $widget += array(
      'type' => $field_type_info['default_widget'],
      'settings' => array(),
      'weight' => 0,
    );

    $widget_type_info = field_info_widget_types($widget['type']);
    // Fall back to default formatter if formatter type is not available.
    if (!$widget_type_info) {
      $widget['type'] = $field_type_info['default_widget'];
      $widget_type_info = field_info_widget_types($widget['type']);
    }
    $widget['module'] = $widget_type_info['module'];
    // Fill in default settings for the widget.
    $widget['settings'] += field_info_widget_settings($widget['type']);

    return $widget;
  }

  /**
   * Adapts display specifications to the current run-time context.
   *
   * @param $display
   *   Display specifications as found in $instance['display']['a_view_mode'].
   * @param $field_type
   *   The field type.
   *
   * @return
   *   The display properties completed for the current runtime context.
   */
  public function prepareInstanceDisplay($display, $field_type) {
    $field_type_info = field_info_field_types($field_type);

    // Fill in default values.
    $display += array(
      'label' => 'above',
      'type' => $field_type_info['default_formatter'],
      'settings' => array(),
      'weight' => 0,
    );
    if ($display['type'] != 'hidden') {
      $formatter_type_info = field_info_formatter_types($display['type']);
      // Fall back to default formatter if formatter type is not available.
      if (!$formatter_type_info) {
        $display['type'] = $field_type_info['default_formatter'];
        $formatter_type_info = field_info_formatter_types($display['type']);
      }
      $display['module'] = $formatter_type_info['module'];
      // Fill in default settings for the formatter.
      $display['settings'] += field_info_formatter_settings($display['type']);
    }

    return $display;
  }

  /**
   * Prepares 'extra fields' for the current run-time context.
   *
   * @param $extra_fields
   *   The array of extra fields, as collected in hook_field_extra_fields().
   * @param $entity_type
   *   The entity type.
   * @param $bundle
   *   The bundle name.
   *
   * @return
   *   The list of extra fields completed for the current runtime context.
   */
  public function prepareExtraFields($extra_fields, $entity_type, $bundle) {
    $entity_type_info = entity_get_info($entity_type);
    $bundle_settings = field_bundle_settings($entity_type, $bundle);
    $extra_fields += array('form' => array(), 'display' => array());

    $result = array();
    // Extra fields in forms.
    foreach ($extra_fields['form'] as $name => $field_data) {
      $settings = isset($bundle_settings['extra_fields']['form'][$name]) ? $bundle_settings['extra_fields']['form'][$name] : array();
      if (isset($settings['weight'])) {
        $field_data['weight'] = $settings['weight'];
      }
      $result['form'][$name] = $field_data;
    }

    // Extra fields in displayed entities.
    $data = $extra_fields['display'];
    foreach ($extra_fields['display'] as $name => $field_data) {
      $settings = isset($bundle_settings['extra_fields']['display'][$name]) ? $bundle_settings['extra_fields']['display'][$name] : array();
      $view_modes = array_merge(array('default'), array_keys($entity_type_info['view modes']));
      foreach ($view_modes as $view_mode) {
        if (isset($settings[$view_mode])) {
          $field_data['display'][$view_mode] = $settings[$view_mode];
        }
        else {
          $field_data['display'][$view_mode] = array(
            'weight' => $field_data['weight'],
            'visible' => TRUE,
          );
        }
      }
      unset($field_data['weight']);
      $result['display'][$name] = $field_data;
    }

    return $result;
  }
}