<?php

/**
 * @file
 * Describe hooks provided by the Views module.
 */

/**
 * @mainpage Views 3 API Manual
 *
 * Much of this information is actually stored in the advanced help; please
 * check the API topic. This help will primarily be aimed at documenting
 * classes and function calls.
 *
 * Topics:
 * - @link views_lifetime The life of a view @endlink
 * - @link views_hooks Views hooks @endlink
 * - @link views_handlers About Views handlers @endlink
 * - @link views_plugins About Views plugins @endlink
 * - @link views_templates Views template files @endlink
 * - @link views_module_handlers Views module handlers @endlink
 */

/**
 * @defgroup views_lifetime The life of a view
 * @{
 * This page explains the basic cycle of a view and what processes happen.
 *
 * @todo.
 * @}
 */

/**
 * @defgroup views_handlers About Views handlers
 * @{
 * In Views, a handler is an object that is part of the view and is part of the
 * query building flow.
 *
 * Handlers are objects; much of the time, the base handlers will work, but
 * often you'll need to override the handler to achieve something meaningful.
 * One typical handler override will be views_handler_filter_operator_in which
 * allows you to have a filter select from a list of options; you'll need to
 * override this to provide your list.
 *
 * Handlers have two distinct code flows; the UI flow and the view building
 * flow.
 *
 * For the query flow:
 * - handler->construct()
 *   - Create the initial handler; at this time it is not yet attached to a
 *     view. It is here that you can set basic defaults if needed, but there
 *     will be no knowledge of the environment yet.
 * - handler->set_definition()
 *   - Set the data from hook_views_data() relevant to the handler.
 * - handler->init()
 *   - Attach the handler to a view, and usually provides the options from the
 *     display.
 * - handler->pre_query()
 *   - Run prior to the query() stage to do early processing.
 * - handler->query()
 *   - Do the bulk of the work this handler needs to do to add itself to the
 *     query.
 *
 * Fields, being the only handlers concerned with output, also have an extended
 * piece of the flow:
 *
 * - handler->pre_render(&$values)
 *   - Called prior to the actual rendering, this allows handlers to query for
 *     extra data; the entire resultset is available here, and this is where
 *     items that have "multiple values" per record can do their extra query for
 *     all of the records available. There are several examples of this at work
 *     in the code, see for example views_handler_field_user_roles.
 * - handler->render()
 *   - This does the actual work of rendering the field.
 *
 * Most handlers are just extensions of existing classes with a few tweaks that
 * are specific to the field in question. For example,
 * views_handler_filter_in_operator provides a simple mechanism to set a
 * multiple-value list for setting filter values. Below,
 * views_handler_filter_node_type overrides the list options, but inherits
 * everything else.
 *
 * @code
 * class views_handler_filter_node_type extends views_handler_filter_in_operator {
 *   function get_value_options() {
 *     if (!isset($this->value_options)) {
 *       $this->value_title = t('Node type');
 *       $types = node_get_types();
 *       foreach ($types as $type => $info) {
 *         $options[$type] = $info->name;
 *       }
 *       $this->value_options = $options;
 *     }
 *   }
 * }
 * @endcode
 *
 * Handlers are stored in their own files and loaded on demand. Like all other
 * module files, they must first be registered through the module's info file.
 * For example:
 *
 * @code
 * name = Example module
 * description = "Gives an example of a module."
 * core = 7.x
 * files[] = example.module
 * files[] = example.install
 *
 * ; Views handlers
 * files[] = includes/views/handlers/example_handler_argument_string.inc
 * @endcode
 *
 * The best place to learn more about handlers and how they work is to explore
 * @link views_handlers Views' handlers @endlink and use existing handlers as a
 * guide and a model. Understanding how views_handler and its child classes work
 * is handy but you can do a lot just following these models. You can also
 * explore the views module directory, particularly node.views.inc.
 *
 * Please note that while all handler names in views are prefixed with views_,
 * you should use your own module's name to prefix your handler names in order
 * to ensure namespace safety. Note that the basic pattern for handler naming
 * goes like this:
 *
 * [module]_handler_[type]_[tablename]_[fieldname].
 *
 * Sometimes table and fieldname are not appropriate, but something that
 * resembles what the table/field would be can be used.
 *
 * See also:
 * - @link views_field_handlers Views field handlers @endlink
 * - @link views_sort_handlers Views sort handlers @endlink
 * - @link views_filter_handlers Views filter handlers @endlink
 * - @link views_argument_handlers Views argument handlers @endlink
 * - @link views_relationship_handlers Views relationship handlers @endlink
 * - @link views_area_handlers Views area handlers @endlink
 * @}
 */

/**
 * @defgroup views_plugins About Views plugins
 *
 * In Views, a plugin is a bit like a handler, but plugins are not directly
 * responsible for building the query. Instead, they are objects that are used
 * to display the view or make other modifications.
 *
 * There are several types of plugins in Views:
 * - Display: Display plugins are responsible for controlling *where* a view
 *   lives; that is, how they are being exposed to other parts of Drupal. Page
 *   and block are the most common displays, as well as the ubiquitous 'master'
 *   (or 'default') display.
 * - Style: Style plugins control how a view is displayed. For the most part
 *   they are object wrappers around theme templates. Styles could for example
 *   be HTML lists or tables.
 * - Row style: Row styles handle each individual record from the main view
 *   table. The two included by default render the entire entity (nodes only),
 *   or selected fields.
 * - Argument default: Argument default plugins allow pluggable ways of
 *   providing default values for contextual filters (previously 'arguments').
 *   This is useful for blocks and other display types lacking a natural
 *   argument input. Examples are plugins to extract node and user IDs from the
 *   URL.
 * - Argument validator: Validator plugins can ensure arguments are valid, and
 *   even do transformations on the arguments. They can also provide replacement
 *   patterns for the view title. For example, the 'content' validator
 *   verifies verifies that the argument value corresponds to a node, loads
 *   that node and provides the node title as a replacement pattern.
 * - Access: Access plugins are responsible for controlling access to the view.
 *   Views includes plugins for checking user roles and individual permissions.
 * - Query: Query plugins generate and execute a query, so they can be seen as
 *   a data backend. The default implementation is using SQL. There are
 *   contributed modules reading data from other sources, see for example the
 *   Views XML Backend module.
 * - Cache: Cache plugins control the storage and loading of caches. Currently
 *   they can do both result and render caching, but maybe one day cache the
 *   generated query.
 * - Pager plugins: Pager plugins take care of everything regarding pagers.
 *   From getting and setting the total amount of items to render the pager and
 *   setting the global pager arrays.
 * - Exposed form plugins: Exposed form plugins are responsible for building,
 *   rendering and controlling exposed forms. They can expose new parts of the
 *   view to the user and more.
 * - Localization plugins: Localization plugins take care how the view options
 *   are translated. There are example implementations for t(), 'no
 *   translation' and i18n.
 * - Display extenders: Display extender plugins allow scaling of views options
 *   horizontally. This means that you can add options and do stuff on all
 *   views displays. One theoretical example is metatags for views.
 *
 * Plugins are registered by implementing hook_views_plugins() in your
 * modulename.views.inc file and returning an array of data.
 * For examples please look at views_views_plugins() in
 * views/includes/plugins.inc as it has examples for all of them.
 *
 * Similar to handlers, make sure that you add your plugin files to the
 * module.info file.
 *
 * The array defining plugins will look something like this:
 * @code
 * return array(
 *   'display' => array(
 *     // ... list of display plugins,
 *    ),
 *   'style' => array(
 *     // ... list of style plugins,
 *    ),
 *   'row' => array(
 *     // ... list of row style plugins,
 *    ),
 *   'argument default' => array(
 *     // ... list of argument default plugins,
 *    ),
 *   'argument validator' => array(
 *     // ... list of argument validator plugins,
 *    ),
 *    'access' => array(
 *     // ... list of access plugins,
 *    ),
 *    'query' => array(
 *      // ... list of query plugins,
 *     ),,
 *    'cache' => array(
 *      // ... list of cache plugins,
 *     ),,
 *    'pager' => array(
 *      // ... list of pager plugins,
 *     ),,
 *    'exposed_form' => array(
 *      // ... list of exposed_form plugins,
 *     ),,
 *    'localization' => array(
 *      // ... list of localization plugins,
 *     ),
 *    'display_extender' => array(
 *      // ... list of display extender plugins,
 *     ),
 * );
 * @endcode
 *
 * Each plugin will be registered with an identifier for the plugin, plus a
 * fairly lengthy list of items that can define how and where the plugin is
 * used. Here is an example of a row style plugin from Views core:
 * @code
 *     'node' => array(
 *       'title' => t('Node'),
 *       'help' => t('Display the node with standard node view.'),
 *       'handler' => 'views_plugin_row_node_view',
 *       // Not necessary for most modules.
 *       'path' => drupal_get_path('module', 'views') . '/modules/node',
 *       'theme' => 'views_view_row_node',
 *       // Only works with 'node' as base.
 *       'base' => array('node'),
 *       'uses options' => TRUE,
 *       'type' => 'normal',
 *     ),
 * @endcode
 *
 * Of particular interest is the *path* directive, which works a little
 * differently from handler registration; each plugin must define its own path,
 * rather than relying on a global info for the paths. For example:
 * @code
 *    'feed' => array(
 *      'title' => t('Feed'),
 *      'help' => t('Display the view as a feed, such as an RSS feed.'),
 *      'handler' => 'views_plugin_display_feed',
 *      'uses hook menu' => TRUE,
 *      'use ajax' => FALSE,
 *      'use pager' => FALSE,
 *      'accept attachments' => FALSE,
 *      'admin' => t('Feed'),
 *      'help topic' => 'display-feed',
 *     ),
 * @endcode
 *
 * Please be sure to prefix your plugin identifiers with your module name to
 * ensure namespace safety; after all, two different modules could try to
 * implement the 'grid2' plugin, and that would cause one plugin to completely
 * fail.
 *
 * @todo Finish this document.
 *
 * See also:
 * - @link views_display_plugins Views display plugins @endlink
 * - @link views_style_plugins Views style plugins @endlink
 * - @link views_row_plugins Views row plugins @endlink
 */

/**
 * @defgroup views_hooks Views hooks
 * @{
 * Hooks that can be implemented by other modules in order to implement the
 * Views API.
 */

/**
 * Describes data tables (or the equivalent) to Views.
 *
 * This hook should be placed in MODULENAME.views.inc and it will be auto
 * loaded. MODULENAME.views.inc must be in the directory specified by the 'path'
 * key returned by MODULENAME_views_api(), or the same directory as the .module
 * file, if 'path' is unspecified.
 *
 * @return array
 *   An associative array describing the data structure. Primary key is the
 *   name used internally by Views for the table(s) – usually the actual table
 *   name. The values for the key entries are described in detail below.
 */
function hook_views_data() {
  // This example describes how to write hook_views_data() for the following
  // table:
  //
  // CREATE TABLE example_table (
  //   nid INT(11) NOT NULL COMMENT 'Primary key; refers to {node}.nid.',
  //   plain_text_field VARCHAR(32) COMMENT 'Just a plain text field.',
  //   numeric_field INT(11) COMMENT 'Just a numeric field.',
  //   boolean_field INT(1) COMMENT 'Just an on/off field.',
  //   timestamp_field INT(8) COMMENT 'Just a timestamp field.',
  //   PRIMARY KEY(nid)
  // );
  // First, the entry $data['example_table']['table'] describes properties of
  // the actual table – not its content.
  // The 'group' index will be used as a prefix in the UI for any of this
  // table's fields, sort criteria, etc. so it's easy to tell where they came
  // from.
  $data['example_table']['table']['group'] = t('Example table');

  // Define this as a base table – a table that can be described in itself by
  // views (and not just being brought in as a relationship). In reality this
  // is not very useful for this table, as it isn't really a distinct object of
  // its own, but it makes a good example.
  $data['example_table']['table']['base'] = array(
    // This is the identifier field for the view.
    'field' => 'nid',
    'title' => t('Example table'),
    'help' => t('Example table contains example content and can be related to nodes.'),
    'weight' => -10,
  );

  // This table references the {node} table. The declaration below creates an
  // 'implicit' relationship to the node table, so that when 'node' is the base
  // table, the fields are automatically available.
  $data['example_table']['table']['join'] = array(
    // Index this array by the table name to which this table refers.
    'node' => array(
      // The primary key in the referenced table.
      'left_field' => 'nid',
      // The foreign key in this table.
      'field' => 'nid',
    ),
  );

  // Next, describe each of the individual fields in this table to Views. This
  // is done by describing $data['example_table']['FIELD_NAME']. This part of
  // the array may then have further entries:
  //   - title: The label for the table field, as presented in Views.
  //   - help: The description text for the table field.
  //   - relationship: A description of any relationship handler for the table
  //     field.
  //   - field: A description of any field handler for the table field.
  //   - sort: A description of any sort handler for the table field.
  //   - filter: A description of any filter handler for the table field.
  //   - argument: A description of any argument handler for the table field.
  //   - area: A description of any handler for adding content to header,
  //     footer or as no result behaviour.
  //
  // The handler descriptions are described with examples below.
  // Node ID table field.
  $data['example_table']['nid'] = array(
    'title' => t('Example content'),
    'help' => t('Some example content that references a node.'),
    // Define a relationship to the {node} table, so example_table views can
    // add a relationship to nodes. If you want to define a relationship the
    // other direction, use hook_views_data_alter(), or use the 'implicit' join
    // method described above.
    'relationship' => array(
      // The name of the table to join with.
      'base' => 'node',
      // The name of the field on the joined table.
      'base field' => 'nid',
      // 'field' => 'nid' -- see hook_views_data_alter(); not needed here.
      'handler' => 'views_handler_relationship',
      'label' => t('Default label for the relationship'),
      'title' => t('Title shown when adding the relationship'),
      'help' => t('More information on this relationship'),
    ),
  );

  // Example plain text field.
  $data['example_table']['plain_text_field'] = array(
    'title' => t('Plain text field'),
    'help' => t('Just a plain text field.'),
    'field' => array(
      'handler' => 'views_handler_field',
      // This is use by the table display plugin.
      'click sortable' => TRUE,
    ),
    'sort' => array(
      'handler' => 'views_handler_sort',
    ),
    'filter' => array(
      'handler' => 'views_handler_filter_string',
    ),
    'argument' => array(
      'handler' => 'views_handler_argument_string',
    ),
  );

  // Example numeric text field.
  $data['example_table']['numeric_field'] = array(
    'title' => t('Numeric field'),
    'help' => t('Just a numeric field.'),
    'field' => array(
      'handler' => 'views_handler_field_numeric',
      'click sortable' => TRUE,
    ),
    'filter' => array(
      'handler' => 'views_handler_filter_numeric',
    ),
    'sort' => array(
      'handler' => 'views_handler_sort',
    ),
  );

  // Example boolean field.
  $data['example_table']['boolean_field'] = array(
    'title' => t('Boolean field'),
    'help' => t('Just an on/off field.'),
    'field' => array(
      'handler' => 'views_handler_field_boolean',
      'click sortable' => TRUE,
    ),
    'filter' => array(
      'handler' => 'views_handler_filter_boolean_operator',
      // Note that you can override the field-wide label.
      'label' => t('Published'),
      // This setting is used by the boolean filter handler, as possible option.
      'type' => 'yes-no',
      // use boolean_field = 1 instead of boolean_field <> 0 in WHERE statement.
      'use equal' => TRUE,
    ),
    'sort' => array(
      'handler' => 'views_handler_sort',
    ),
  );

  // Example timestamp field.
  $data['example_table']['timestamp_field'] = array(
    'title' => t('Timestamp field'),
    'help' => t('Just a timestamp field.'),
    'field' => array(
      'handler' => 'views_handler_field_date',
      'click sortable' => TRUE,
    ),
    'sort' => array(
      'handler' => 'views_handler_sort_date',
    ),
    'filter' => array(
      'handler' => 'views_handler_filter_date',
    ),
  );

  return $data;
}

/**
 * Alter table structure.
 *
 * You can add/edit/remove existing tables defined by hook_views_data().
 *
 * This hook should be placed in MODULENAME.views_default.inc and it will be
 * auto-loaded. MODULENAME.views_default.inc must be in the directory specified
 * by the 'path' key returned by MODULENAME_views_api(), or the same directory
 * as the .module file, if 'path' is unspecified.
 *
 * After adding this hook to an existing module, you will need to clear the
 * Drupal menu cache and the Views cache to have your default views be
 * recognized.
 *
 * @param array $data
 *   An array of all Views data, passed by reference. See hook_views_data() for
 *   structure.
 *
 * @see hook_views_data()
 */
function hook_views_data_alter(&$data) {
  // This example alters the title of the node:nid field in the Views UI.
  $data['node']['nid']['title'] = t('Node-Nid');

  // This example adds an example field to the users table.
  $data['users']['example_field'] = array(
    'title' => t('Example field'),
    'help' => t('Some example content that references a user'),
    'field' => array(
      'handler' => 'modulename_handler_field_example_field',
    ),
  );

  // This example changes the handler of the node title field.
  // In this handler you could do stuff, like preview of the node when clicking
  // the node title.
  $data['node']['title']['field']['handler'] = 'modulename_handler_field_node_title';

  // This example adds a relationship to table {foo}, so that 'foo' views can
  // add this table using a relationship. Because we don't want to write over
  // the primary key field definition for the {foo}.fid field, we use a
  // placeholder field name as the key.
  $data['foo']['sample_name'] = array(
    'title' => t('Example relationship'),
    'help' => t('Example help'),
    'relationship' => array(
      // Table we're joining to.
      'base' => 'example_table',
      // Field on the joined table.
      'base field' => 'eid',
      // Real field name on the 'foo' table.
      'field' => 'fid',
      'handler' => 'views_handler_relationship',
      'label' => t('Default label for relationship'),
      'title' => t('Title seen when adding relationship'),
      'help' => t('More information about relationship.'),
    ),
  );

  // Note that the $data array is not returned – it is modified by reference.
}

/**
 * Override the default data for a Field API field.
 *
 * Field module's Implements hook_views_data() invokes this for each
 * field in the module that defines the field type (as declared in the field
 * array). It is not invoked in other modules.
 *
 * If no hook implementation exists, hook_views_data() falls back to
 * field_views_field_default_views_data().
 *
 * @param array $field
 *   A field definition array, as returned by field_info_fields().
 *
 * @return array
 *   An array of views data, in the same format as the return value of
 *   hook_views_data().
 *
 * @see field_views_data()
 * @see hook_field_views_data_alter()
 * @see hook_field_views_data_views_data_alter()
 */
function hook_field_views_data($field) {
  return array();
}

/**
 * Alter the views data for a single Field API field.
 *
 * This is called even if there is no hook_field_views_data() implementation for
 * the field, and therefore may be used to alter the default data that
 * field_views_field_default_views_data() supplies for the field.
 *
 * @param array $result
 *   An array of views table data provided for a single field. This has the same
 *   format as the return value of hook_views_data().
 * @param array $field
 *   A field definition array, as returned by field_info_fields().
 * @param string $module
 *   The module that defines the field type.
 *
 * @see field_views_data()
 * @see hook_field_views_data()
 * @see hook_field_views_data_views_data_alter()
 */
function hook_field_views_data_alter(&$result, $field, $module) {

}

/**
 * Alter the views data on a per field basis.
 *
 * Field module's Implements hook_views_data_alter() invokes this for
 * each field in the module that defines the field type (as declared in the
 * field array). It is not invoked in other modules.
 *
 * Unlike hook_field_views_data_alter(), this operates on the whole of the views
 * data. This allows a field module to add data that concerns its fields to
 * other tables, which would not yet be defined at the point when
 * hook_field_views_data() and hook_field_views_data_alter() are invoked. For
 * example, entityreference adds reverse relationships on the tables for the
 * entities which are referenced by entityreference fields.
 *
 * (Note: this is weirdly named so as not to conflict with
 * hook_field_views_data_alter().)
 *
 * @see hook_field_views_data()
 * @see hook_field_views_data_alter()
 * @see field_views_data_alter()
 */
function hook_field_views_data_views_data_alter(&$data, $field) {
  $field_name = $field['field_name'];
  $data_key = 'field_data_' . $field_name;
  // Views data for this field is in $data[$data_key]
}

/**
 * Describes plugins defined by the module.
 *
 * This hook should be placed in MODULENAME.views.inc and it will be
 * auto-loaded. MODULENAME.views.inc must be in the directory specified by the
 * 'path' key returned by MODULENAME_views_api(), or the same directory as the
 * .module file, if 'path' is unspecified. All plugin files need to be
 * referenced in MODULENAME.info with the files[] directive.
 *
 * @return array
 *   An array on the form $plugins['PLUGIN TYPE']['PLUGIN NAME']. The plugin
 *   must be one of row, display, display_extender, style, argument default,
 *   argument validator, access, query, cache, pager, exposed_form or
 *   localization. The plugin name should be prefixed with your module name.
 *   The value for each entry is an associative array that may contain the
 *   following entries:
 *   - Used by all plugin types:
 *     - title (required): The name of the plugin, as shown in Views. Wrap in
 *       t().
 *     - handler (required): The name of the file containing the class
 *       describing the handler, which must also be the name of the handler's
 *       class.
 *     - path: Path to the handler. Only required if the handler is not placed
 *       in the same folder as the .module file or in the subfolder 'views'.
 *     - parent: The name of the plugin this plugin extends. Since Drupal 7 this
 *       is no longer required, but may still be useful from a code readability
 *       perspective.
 *     - no ui: Set to TRUE to denote that the plugin doesn't appear to be
 *       selectable in the ui, though on the api side they still exists.
 *     - uses options: Set to TRUE to denote that the plugin has an additional
 *       options form.
 *     - help: A short help text, wrapped in t() used as description on the
 *       plugin settings form.
 *     - help topic: The name of an entry by advanced help for the plugin.
 *     - theme: The name of a theme suggestion to use for the display.
 *     - js: An array with paths to js files that should be included for the
 *       display. Note that the path should be relative Drupal root, not module
 *       root.
 *     - type: Each plugin can specify a type parameter to group certain
 *       plugins together. For example all row plugins related to feeds are
 *       grouped together, because a rss style plugin only accepts feed row
 *       plugins.
 *
 *   - Used by display plugins:
 *     - admin: The administrative name of the display, as displayed on the
 *       Views overview and also used as default name for new displays. Wrap in
 *       t().
 *     - no remove: Set to TRUE to make the display non-removable. (Basically
 *       only used for the master/default display.)
 *     - use ajax: Set to TRUE to allow AJAX loads in the display. If it's
 *       disabled there will be no ajax option in the ui.
 *     - use pager: Set to TRUE to allow paging in the display.
 *     - use more: Set to TRUE to allow the 'use more' setting in the display.
 *     - accept attachments: Set to TRUE to allow attachment displays to be
 *       attached to this display type.
 *     - contextual links locations: An array with places where contextual links
 *       should be added. Can for example be 'page' or 'block'. If you don't
 *       specify it there will be contextual links around the rendered view. If
 *       this is not set or regions have been specified, views will display an
 *       option to 'hide contextual links'. Use an empty array if you do not
 *       want this.
 *     - uses hook menu: Set to TRUE to have the display included by
 *       views_menu_alter(). views_menu_alter executes then execute_hook_menu
 *       on the display object.
 *     - uses hook block: Set to TRUE to have the display included by
 *       views_block_info().
 *     - theme: The name of a theme suggestion to use for the display.
 *     - js: An array with paths to js files that should be included for the
 *       display. Note that the path should be relative Drupal root, not module
 *       root.
 *
 *   - Used by style plugins:
 *     - uses row plugin: Set to TRUE to allow row plugins for this style.
 *     - uses row class: Set to TRUE to allow the CSS class settings for rows.
 *     - uses fields: Set to TRUE to have the style plugin accept field
 *       handlers.
 *     - uses grouping: Set to TRUE to allow the grouping settings for rows.
 *     - even empty: May have the value 'even empty' to tell Views that the
 *       style should be rendered even if there are no results.
 *
 *   - Used by row plugins:
 *     - uses fields: Set to TRUE to have the row plugin accept field handlers.
 */
function hook_views_plugins() {
  $plugins = array();
  $plugins['argument validator'] = array(
    'taxonomy_term' => array(
      'title' => t('Taxonomy term'),
      'handler' => 'views_plugin_argument_validate_taxonomy_term',
      // Declaring path explicitly not necessary for most modules.
      'path' => drupal_get_path('module', 'views') . '/modules/taxonomy',
    ),
  );

  return array(
    // This just tells our themes are elsewhere.
    'module' => 'views',
    'argument validator' => array(
      'taxonomy_term' => array(
        'title' => t('Taxonomy term'),
        'handler' => 'views_plugin_argument_validate_taxonomy_term',
        // Declaring path explicitly not necessary for most modules.
        'path' => drupal_get_path('module', 'views') . '/modules/taxonomy',
      ),
    ),
    'argument default' => array(
      'taxonomy_tid' => array(
        'title' => t('Taxonomy term ID from URL'),
        'handler' => 'views_plugin_argument_default_taxonomy_tid',
        'path' => drupal_get_path('module', 'views') . '/modules/taxonomy',
        'parent' => 'fixed',
      ),
    ),
  );
}

/**
 * Alter existing plugins data, defined by modules.
 *
 * @see hook_views_plugins()
 */
function hook_views_plugins_alter(&$plugins) {
  // Add apachesolr to the base of the node row plugin.
  $plugins['row']['node']['base'][] = 'apachesolr';
}

/**
 * Alter existing plugin option definitions.
 *
 * This can be used to edit default or add new option definitions to existing
 * plugins. The reason for doing this is that only overriding the relevent form
 * with hook_form_alter() is insufficent because submitted form values will be
 * ignored if they haven't been declared as an available option.
 *
 * An alternative approach you could also take is to extend each plugin
 * individually. However if your goal is to override many, or even all plugins,
 * this results in a lot of additional code and files. This makes it a lot more
 * troublesome to maintain the codebase, as well as interoperability with other
 * modules.
 *
 * @param array $options
 *  The option definitions to be altered.
 * @param $plugin
 *  A views object of the plugin where the default options are defined.
 *
 * @see views_object::option_definition()
 * @see hook_views_handler_option_definition_alter()
 * @see hook_form_alter()
 */
function hook_views_plugin_option_definition_alter(&$options, $plugin) {
  // Add a new option definition.
  $options['option_name'] = array('default' => '');
}

/**
 * Alter existing handler option definitions.
 *
 * This can be used to edit default or add new option definitions to existing
 * handlers. The reason for doing this is that only overriding the relevent form
 * with hook_form_alter() is insufficent because submitted form values will be
 * ignored if they haven't been declared as an available option.
 *
 * An alternative approach you could also take is to extend each handler
 * individually. However if your goal is to override many, or even all handlers,
 * this results in a lot of additional code and files. This makes it a lot more
 * troublesome to maintain the codebase, as well as interoperability with other
 * modules.
 *
 * @param array $options
 *  The option definitions to be altered.
 * @param $handler
 *  A views object of the handler where the default options are defined.
 *
 * @see views_handler::option_definition()
 * @see hook_views_plugin_option_definition_alter()
 * @see hook_form_alter()
 */
function hook_views_handler_option_definition_alter(&$options, $handler) {
  // Add a new option definition.
  $options['option_name'] = array('default' => '');
}

/**
 * Register View API information.
 *
 * This is required for your module to have its include files loaded; for
 * example, when implementing hook_views_default_views().
 *
 * @return array
 *   An array with the following possible keys:
 *   - api: (required) The version of the Views API the module implements.
 *   - path: (optional) If includes are stored somewhere other than within the
 *     root module directory, specify its path here.
 *   - template path: (optional) A path where the module has stored its views
 *     template files. When you have specified this key views automatically
 *     uses the template files for the views. You can use the same naming
 *     conventions like for normal views template files.
 */
function hook_views_api() {
  return array(
    'api' => 3,
    'path' => drupal_get_path('module', 'example') . '/includes/views',
    'template path' => drupal_get_path('module', 'example') . '/themes',
  );
}

/**
 * Allows modules to provide their own views.
 *
 * These can either be used as-is or as a "starter" for users to build from.
 *
 * This hook should be placed in MODULENAME.views_default.inc and it will be
 * auto-loaded. MODULENAME.views_default.inc must be in the directory specified
 * by the 'path' key returned by MODULENAME_views_api(), or the same directory
 * as the .module file, if 'path' is unspecified.
 *
 * The $view->disabled boolean flag indicates whether the View should be
 * enabled (FALSE) or disabled (TRUE) by default.
 *
 * @return array
 *   An associative array containing the structures of views, as generated from
 *   the Export tab, keyed by the view name. A best practice is to go through
 *   and add t() to all title and label strings, with the exception of menu
 *   strings.
 */
function hook_views_default_views() {
  // Begin copy and paste of output from the Export tab of a view.
  $view = new view();
  $view->name = 'frontpage';
  $view->description = 'Emulates the default Drupal front page; you may set the default home page path to this view to make it your front page.';
  $view->tag = 'default';
  $view->base_table = 'node';
  $view->human_name = 'Front page';
  $view->core = 0;
  $view->api_version = '3.0';
  $view->disabled = FALSE; /* Edit this to true to make a default view disabled initially */

  /* Display: Master */
  $handler = $view->new_display('default', 'Master', 'default');
  $handler->display->display_options['access']['type'] = 'none';
  $handler->display->display_options['cache']['type'] = 'none';
  $handler->display->display_options['query']['type'] = 'views_query';
  $handler->display->display_options['query']['options']['query_comment'] = FALSE;
  $handler->display->display_options['exposed_form']['type'] = 'basic';
  $handler->display->display_options['pager']['type'] = 'full';
  $handler->display->display_options['style_plugin'] = 'default';
  $handler->display->display_options['row_plugin'] = 'node';
  /* Sort criterion: Content: Sticky */
  $handler->display->display_options['sorts']['sticky']['id'] = 'sticky';
  $handler->display->display_options['sorts']['sticky']['table'] = 'node';
  $handler->display->display_options['sorts']['sticky']['field'] = 'sticky';
  $handler->display->display_options['sorts']['sticky']['order'] = 'DESC';
  /* Sort criterion: Content: Post date */
  $handler->display->display_options['sorts']['created']['id'] = 'created';
  $handler->display->display_options['sorts']['created']['table'] = 'node';
  $handler->display->display_options['sorts']['created']['field'] = 'created';
  $handler->display->display_options['sorts']['created']['order'] = 'DESC';
  /* Filter criterion: Content: Promoted to front page */
  $handler->display->display_options['filters']['promote']['id'] = 'promote';
  $handler->display->display_options['filters']['promote']['table'] = 'node';
  $handler->display->display_options['filters']['promote']['field'] = 'promote';
  $handler->display->display_options['filters']['promote']['value'] = '1';
  $handler->display->display_options['filters']['promote']['group'] = 0;
  $handler->display->display_options['filters']['promote']['expose']['operator'] = FALSE;
  /* Filter criterion: Content: Published */
  $handler->display->display_options['filters']['status']['id'] = 'status';
  $handler->display->display_options['filters']['status']['table'] = 'node';
  $handler->display->display_options['filters']['status']['field'] = 'status';
  $handler->display->display_options['filters']['status']['value'] = '1';
  $handler->display->display_options['filters']['status']['group'] = 0;
  $handler->display->display_options['filters']['status']['expose']['operator'] = FALSE;

  /* Display: Page */
  $handler = $view->new_display('page', 'Page', 'page');
  $handler->display->display_options['path'] = 'frontpage';

  /* Display: Feed */
  $handler = $view->new_display('feed', 'Feed', 'feed');
  $handler->display->display_options['defaults']['title'] = FALSE;
  $handler->display->display_options['title'] = 'Front page feed';
  $handler->display->display_options['pager']['type'] = 'some';
  $handler->display->display_options['style_plugin'] = 'rss';
  $handler->display->display_options['row_plugin'] = 'node_rss';
  $handler->display->display_options['path'] = 'rss.xml';
  $handler->display->display_options['displays'] = array(
    'default' => 'default',
    'page' => 'page',
  );
  $handler->display->display_options['sitename_title'] = '1';

  // (Export ends here.)
  // Add view to list of views to provide.
  $views[$view->name] = $view;

  // Repeat all of the above for each view the module should provide. At the
  // end, return array of default views.
  return $views;
}

/**
 * Alter default views defined by other modules.
 *
 * This hook is called right before all default views are cached to the
 * database. It takes a keyed array of views by reference.
 *
 * Example usage to add a field to a view:
 * @code
 *   $handler =& $view->display['DISPLAY_ID']->handler;
 *   // Add the user name field to the view.
 *   $handler->display->display_options['fields']['name']['id'] = 'name';
 *   $handler->display->display_options['fields']['name']['table'] = 'users';
 *   $handler->display->display_options['fields']['name']['field'] = 'name';
 *   $handler->display->display_options['fields']['name']['label'] = 'Author';
 *   $handler->display->display_options['fields']['name']['link_to_user'] = 1;
 * @endcode
 */
function hook_views_default_views_alter(&$views) {
  if (isset($views['taxonomy_term'])) {
    $views['taxonomy_term']->display['default']->display_options['title'] = 'Categories';
  }
}

/**
 * Performs replacements in the query before being performed.
 *
 * @param object $view
 *   The View being executed.
 *
 * @return array
 *   An array with keys being the strings to replace, and the values the strings
 *   to replace them with. The strings to replace are often surrounded with
 *   '***', as illustrated in the example implementation.
 */
function hook_views_query_substitutions($view) {
  // Example from views_views_query_substitutions().
  global $language_content;
  return array(
    '***CURRENT_VERSION***' => VERSION,
    '***CURRENT_TIME***' => REQUEST_TIME,
    '***CURRENT_LANGUAGE***' => $language_content->language,
    '***DEFAULT_LANGUAGE***' => language_default('language'),
  );
}

/**
 * This hook is called to get a list of placeholders and their substitutions.
 *
 * Used when preprocessing a View with form elements.
 *
 * @return array
 *   An array with keys being the strings to replace, and the values the strings
 *   to replace them with.
 */
function hook_views_form_substitutions() {
  return array(
    '<!--views-form-example-substitutions-->' => 'Example Substitution',
  );
}

/**
 * Allows altering a view at the very beginning of processing a preview.
 *
 * Occurs before anything is done.
 *
 * This hook is only triggered when the one of the following are invoked:
 * - $view->execute_display()
 * - $view->preview()
 *
 * As such code placed in this hook will not fire during:
 * - $view->build()
 * - $view->execute()
 * - $view->render()
 *
 * Likely, hook_views_pre_build() or hook_views_pre_execute() are much better
 * choices for most use cases since they are always invoked, not just when
 * previewing a display.
 *
 * Adding output to the view can be accomplished by placing text on
 * $view->attachment_before and $view->attachment_after.
 *
 * @param object $view
 *   The view object about to be processed.
 * @param string $display_id
 *   The machine name of the active display.
 * @param array $args
 *   An array of arguments passed into the view.
 */
function hook_views_pre_view(&$view, &$display_id, &$args) {
  // Change the display if the acting user has 'administer site configuration'
  // permission, to display something radically different.
  // (Note that this is not necessarily the best way to solve that task. Feel
  // free to contribute another example!)
  if (
    $view->name == 'my_special_view'
    && user_access('administer site configuration')
    && $display_id == 'public_display'
  ) {
    $view->set_display('private_display');
  }
}

/**
 * Called after the display's pre_execute phase but before the build process.
 *
 * Adding output to the view can be accomplished by placing text on
 * $view->attachment_before and $view->attachment_after.
 *
 * @param object $view
 *   The view object about to be processed.
 */
function hook_views_pre_build(&$view) {
  // Because of some inexplicable business logic, we should remove all
  // attachments from all views on Mondays.
  // (This alter could be done later in the execution process as well.)
  if (date('D') == 'Mon') {
    unset($view->attachment_before);
    unset($view->attachment_after);
  }
}

/**
 * This hook is called right after the build process.
 *
 * The query is now fully built, but it has not yet been run through
 * db_rewrite_sql.
 *
 * Adding output to the view can be accomplished by placing text on
 * $view->attachment_before and $view->attachment_after.
 *
 * @param object $view
 *   The view object about to be processed.
 */
function hook_views_post_build(&$view) {
  // If the exposed field 'type' is set, hide the column containing the content
  // type. (Note that this is a solution for a particular view, and makes
  // assumptions about both exposed filter settings and the fields in the view.
  // Also note that this alter could be done at any point before the view being
  // rendered.)
  if ($view->name == 'my_view' && isset($view->exposed_raw_input['type']) && $view->exposed_raw_input['type'] != 'All') {
    // 'Type' should be interpreted as content type.
    if (isset($view->field['type'])) {
      $view->field['type']->options['exclude'] = TRUE;
    }
  }
}

/**
 * This hook is called right before the execute process.
 *
 * The query is now fully built, but it has not yet been run through
 * db_rewrite_sql.
 *
 * Adding output to the view can be accomplished by placing text on
 * $view->attachment_before and $view->attachment_after.
 *
 * @param object $view
 *   The view object about to be processed.
 */
function hook_views_pre_execute(&$view) {
  // Whenever a view queries more than two tables, show a message that notifies
  // view administrators that the query might be heavy.
  // (This action could be performed later in the execution process, but not
  // earlier.)
  if (count($view->query->tables) > 2 && user_access('administer views')) {
    drupal_set_message(t('The view %view may be heavy to execute.', array('%view' => $view->name)), 'warning');
  }
}

/**
 * This hook is called right after the execute process.
 *
 * The query has been executed, but the pre_render() phase has not yet happened
 * for handlers.
 *
 * Adding output to the view can be accomplished by placing text on
 * $view->attachment_before and $view->attachment_after. Altering the content
 * can be achieved by editing the items of $view->result.
 *
 * @param object $view
 *   The view object about to be processed.
 */
function hook_views_post_execute(&$view) {
  // If there are more than 100 results, show a message that encourages the user
  // to change the filter settings.
  // (This action could be performed later in the execution process, but not
  // earlier.)
  if ($view->total_rows > 100) {
    drupal_set_message(t('You have more than 100 hits. Use the filter settings to narrow down your list.'));
  }
}

/**
 * This hook is called right before the render process.
 *
 * The query has been executed, and the pre_render() phase has already happened
 * for handlers, so all data should be available.
 *
 * Adding output to the view can be accomplished by placing text on
 * $view->attachment_before and $view->attachment_after. Altering the content
 * can be achieved by editing the items of $view->result.
 *
 * This hook can be utilized by themes.
 *
 * @param object $view
 *   The view object about to be processed.
 */
function hook_views_pre_render(&$view) {
  // Scramble the order of the rows shown on this result page.
  // Note that this could be done earlier, but not later in the view execution
  // process.
  shuffle($view->result);
}

/**
 * Post process any rendered data.
 *
 * This can be valuable to be able to cache a view and still have some level of
 * dynamic output. In an ideal world, the actual output will include HTML
 * comment based tokens, and then the post process can replace those tokens.
 *
 * Example usage. If it is known that the view is a node view and that the
 * primary field will be a nid, you can do something like this:
 *
 * <!--post-FIELD-NID-->
 *
 * And then in the post render, create an array with the text that should
 * go there:
 *
 * strtr($output, array('<!--post-FIELD-1-->' => 'output for FIELD of nid 1');
 *
 * All of the cached result data will be available in $view->result, as well,
 * so all ids used in the query should be discoverable.
 *
 * This hook can be utilized by themes.
 *
 * @param object $view
 *   The view object about to be processed.
 * @param string $output
 *   A flat string with the rendered output of the view.
 * @param array $cache
 *   The cache settings.
 */
function hook_views_post_render(&$view, &$output, &$cache) {
  // When using full pager, disable any time-based caching if there are less
  // then 10 results.
  if ($view->query->pager instanceof views_plugin_pager_full && $cache->options['type'] == 'time' && count($view->result) < 10) {
    $cache['options']['results_lifespan'] = 0;
    $cache['options']['output_lifespan'] = 0;
  }
}

/**
 * Alter the query before executing the query.
 *
 * This hook should be placed in MODULENAME.views.inc and it will be
 * auto-loaded. MODULENAME.views.inc must be in the directory specified by the
 * 'path' key returned by MODULENAME_views_api(), or the same directory as the
 * .module file, if 'path' is unspecified.
 *
 * @param object $view
 *   The view object about to be processed.
 * @param object $query
 *   An object describing the query.
 *
 * @see hook_views_query_substitutions()
 */
function hook_views_query_alter(&$view, &$query) {
  // (Example assuming a view with an exposed filter on node title.)
  // If the input for the title filter is a positive integer, filter against
  // node ID instead of node title.
  if ($view->name == 'my_view' && is_numeric($view->exposed_raw_input['title']) && $view->exposed_raw_input['title'] > 0) {
    // Traverse through the 'where' part of the query.
    foreach ($query->where as &$condition_group) {
      foreach ($condition_group['conditions'] as &$condition) {
        // If this is the part of the query filtering on title, change the
        // condition to filter on node ID.
        if ($condition['field'] == 'node.title') {
          $condition = array(
            'field' => 'node.nid',
            'value' => $view->exposed_raw_input['title'],
            'operator' => '=',
          );
        }
      }
    }
  }
}

/**
 * Alter the information box that (optionally) appears with a view preview.
 *
 * Includes query and performance statistics.
 *
 * This hook should be placed in MODULENAME.views.inc and it will be
 * auto-loaded. MODULENAME.views.inc must be in the directory specified by the
 * 'path' key returned by MODULENAME_views_api(), or the same directory as the
 * .module file, if 'path' is unspecified.
 *
 * Warning: $view is not a reference in PHP4 and cannot be modified here. But it
 * IS a reference in PHP5, and can be modified. Please be careful with it.
 *
 * @param array $rows
 *   An associative array with two keys:
 *   - query: An array of rows suitable for theme('table'), containing
 *     information about the query and the display title and path.
 *   - statistics: An array of rows suitable for theme('table'), containing
 *     performance statistics.
 * @param object $view
 *   The view object.
 *
 * @see theme_table()
 */
function hook_views_preview_info_alter(&$rows, $view) {
  // Adds information about the tables being queried by the view to the query
  // part of the info box.
  $rows['query'][] = array(
    t('<strong>Table queue</strong>'),
    count($view->query->table_queue) . ': (' . implode(', ', array_keys($view->query->table_queue)) . ')',
  );
}

/**
 * This hooks allows to alter the links at the top of the view edit form.
 *
 * Some modules might want to add links there.
 *
 * @param array $links
 *   An array of links which will be displayed at the top of the view edit form.
 *   Each entry should be on a form suitable for theme('link').
 * @param object $view
 *   The full view object which is currently edited.
 * @param string $display_id
 *   The current display id which is edited. For example that's 'default' or
 *   'page_1'.
 */
function hook_views_ui_display_top_links_alter(&$links, $view, $display_id) {
  // Put the export link first in the list.
  if (isset($links['export'])) {
    $links = array('export' => $links['export']) + $links;
  }
}

/**
 * Allows altering the commands which are used on a views AJAX request.
 *
 * @param array $commands
 *   An array of ajax commands.
 * @param object $view
 *   The view which is requested.
 */
function hook_views_ajax_data_alter(&$commands, $view) {
  // Replace Views' method for scrolling to the top of the element with your
  // custom scrolling method.
  foreach ($commands as &$command) {
    if ($command['command'] == 'viewsScrollTop') {
      $command['command'] .= 'myScrollTop';
    }
  }
}

/**
 * Allow modules to respond to the Views cache being invalidated.
 *
 * This hook should fire whenever a view is enabled, disabled, created,
 * updated, or deleted.
 *
 * @param string $cid
 *   The cache identifier that is being cleared.
 *
 * @see views_invalidate_cache()
 */
function hook_views_invalidate_cache($cid) {
  cache_clear_all('views:*', 'cache_mymodule', TRUE);
}

/**
 * Allow modules to alter a view prior to being saved.
 */
function hook_views_view_presave($view) {
  // Do some adjustments to the view. Handle with care.
  if (mymodule_check_view($view)) {
    mymodule_do_some_voodoo($view);
  }
}

/**
 * Allow modules to respond to a view being saved.
 */
function hook_views_view_save($view) {
  // Make a watchdog entry.
  watchdog('views', 'The view @name was deleted by @user at @time', array('@name' => $view->name, '@user' => $GLOBALS['user']->name, '@time' => format_date(time())));
}

/**
 * Allow modules to respond to a view being deleted or reverted.
 */
function hook_views_view_delete($view) {
  // Make a watchdog entry.
  watchdog('views', 'The view @name was deleted by @user at @time', array('@name' => $view->name, '@user' => $GLOBALS['user']->name, '@time' => format_date(time())));
}

/**
 * @}
 */

/**
 * @defgroup views_module_handlers Views module handlers
 * @{
 * Handlers exposed by various modules to Views.
 * @}
 */