that shows the Privacy Policy content of the site.
 *
 * is_privacy_policy() is dependent on the site's "Change your Privacy Policy page" Privacy Settings 'wp_page_for_privacy_policy'.
 *
 * This function will return true only on the page you set as the "Privacy Policy page".
 *
 * For more information on this and similar theme functions, check out
 * the {@link https://developer.wordpress.org/themes/basics/conditional-tags/
 * Conditional Tags} article in the Theme Developer Handbook.
 *
 * @since 5.2.0
 *
 * @global WP_Query $wp_query WordPress Query object.
 *
 * @return bool Whether the query is for the Privacy Policy page.
 */
function is_privacy_policy() {
	global $wp_query;

	if ( ! isset( $wp_query ) ) {
		_doing_it_wrong( __FUNCTION__, __( 'Conditional query tags do not work before the query is run. Before then, they always return false.' ), '3.1.0' );
		return false;
	}

	return $wp_query->is_privacy_policy();
}

/**
 * Determines whether the query is for an existing month archive.
 *
 * For more information on this and similar theme functions, check out
 * the {@link https://developer.wordpress.org/themes/basics/conditional-tags/
 * Conditional Tags} article in the Theme Developer Handbook.
 *
 * @since 1.5.0
 *
 * @global WP_Query $wp_query WordPress Query object.
 *
 * @return bool Whether the query is for an existing month archive.
 */
function is_month() {
	global $wp_query;

	if ( ! isset( $wp_query ) ) {
		_doing_it_wrong( __FUNCTION__, __( 'Conditional query tags do not work before the query is run. Before then, they always return false.' ), '3.1.0' );
		return false;
	}

	return $wp_query->is_month();
}

/**
 * Determines whether the query is for an existing single page.
 *
 * If the $page parameter is specified, this function will additionally
 * check if the query is for one of the pages specified.
 *
 * For more information on this and similar theme functions, check out
 * the {@link https://developer.wordpress.org/themes/basics/conditional-tags/
 * Conditional Tags} article in the Theme Developer Handbook.
 *
 * @since 1.5.0
 *
 * @see is_single()
 * @see is_singular()
 * @global WP_Query $wp_query WordPress Query object.
 *
 * @param int|string|int[]|string[] $page Optional. Page ID, title, slug, or array of such
 *                                        to check against. Default empty.
 * @return bool Whether the query is for an existing single page.
 */
function is_page( $page = '' ) {
	global $wp_query;

	if ( ! isset( $wp_query ) ) {
		_doing_it_wrong( __FUNCTION__, __( 'Conditional query tags do not work before the query is run. Before then, they always return false.' ), '3.1.0' );
		return false;
	}

	return $wp_query->is_page( $page );
}

/**
 * Determines whether the query is for a paged result and not for the first page.
 *
 * For more information on this and similar theme functions, check out
 * the {@link https://developer.wordpress.org/themes/basics/conditional-tags/
 * Conditional Tags} article in the Theme Developer Handbook.
 *
 * @since 1.5.0
 *
 * @global WP_Query $wp_query WordPress Query object.
 *
 * @return bool Whether the query is for a paged result.
 */
function is_paged() {
	global $wp_query;

	if ( ! isset( $wp_query ) ) {
		_doing_it_wrong( __FUNCTION__, __( 'Conditional query tags do not work before the query is run. Before then, they always return false.' ), '3.1.0' );
		return false;
	}

	return $wp_query->is_paged();
}

/**
 * Determines whether the query is for a post or page preview.
 *
 * For more information on this and similar theme functions, check out
 * the {@link https://developer.wordpress.org/themes/basics/conditional-tags/
 * Conditional Tags} article in the Theme Developer Handbook.
 *
 * @since 2.0.0
 *
 * @global WP_Query $wp_query WordPress Query object.
 *
 * @return bool Whether the query is for a post or page preview.
 */
function is_preview() {
	global $wp_query;

	if ( ! isset( $wp_query ) ) {
		_doing_it_wrong( __FUNCTION__, __( 'Conditional query tags do not work before the query is run. Before then, they always return false.' ), '3.1.0' );
		return false;
	}

	return $wp_query->is_preview();
}

/**
 * Is the query for the robots.txt file?
 *
 * @since 2.1.0
 *
 * @global WP_Query $wp_query WordPress Query object.
 *
 * @return bool Whether the query is for the robots.txt file.
 */
function is_robots() {
	global $wp_query;

	if ( ! isset( $wp_query ) ) {
		_doing_it_wrong( __FUNCTION__, __( 'Conditional query tags do not work before the query is run. Before then, they always return false.' ), '3.1.0' );
		return false;
	}

	return $wp_query->is_robots();
}

/**
 * Is the query for the favicon.ico file?
 *
 * @since 5.4.0
 *
 * @global WP_Query $wp_query WordPress Query object.
 *
 * @return bool Whether the query is for the favicon.ico file.
 */
function is_favicon() {
	global $wp_query;

	if ( ! isset( $wp_query ) ) {
		_doing_it_wrong( __FUNCTION__, __( 'Conditional query tags do not work before the query is run. Before then, they always return false.' ), '3.1.0' );
		return false;
	}

	return $wp_query->is_favicon();
}

/**
 * Determines whether the query is for a search.
 *
 * For more information on this and similar theme functions, check out
 * the {@link https://developer.wordpress.org/themes/basics/conditional-tags/
 * Conditional Tags} article in the Theme Developer Handbook.
 *
 * @since 1.5.0
 *
 * @global WP_Query $wp_query WordPress Query object.
 *
 * @return bool Whether the query is for a search.
 */
function is_search() {
	global $wp_query;

	if ( ! isset( $wp_query ) ) {
		_doing_it_wrong( __FUNCTION__, __( 'Conditional query tags do not work before the query is run. Before then, they always return false.' ), '3.1.0' );
		return false;
	}

	return $wp_query->is_search();
}

/**
 * Determines whether the query is for an existing single post.
 *
 * Works for any post type, except attachments and pages
 *
 * If the $post parameter is specified, this function will additionally
 * check if the query is for one of the Posts specified.
 *
 * For more information on this and similar theme functions, check out
 * the {@link https://developer.wordpress.org/themes/basics/conditional-tags/
 * Conditional Tags} article in the Theme Developer Handbook.
 *
 * @since 1.5.0
 *
 * @see is_page()
 * @see is_singular()
 * @global WP_Query $wp_query WordPress Query object.
 *
 * @param int|string|int[]|string[] $post Optional. Post ID, title, slug, or array of such
 *                                        to check against. Default empty.
 * @return bool Whether the query is for an existing single post.
 */
function is_single( $post = '' ) {
	global $wp_query;

	if ( ! isset( $wp_query ) ) {
		_doing_it_wrong( __FUNCTION__, __( 'Conditional query tags do not work before the query is run. Before then, they always return false.' ), '3.1.0' );
		return false;
	}

	return $wp_query->is_single( $post );
}

/**
 * Determines whether the query is for an existing single post of any post type
 * (post, attachment, page, custom post types).
 *
 * If the $post_types parameter is specified, this function will additionally
 * check if the query is for one of the Posts Types specified.
 *
 * For more information on this and similar theme functions, check out
 * the {@link https://developer.wordpress.org/themes/basics/conditional-tags/
 * Conditional Tags} article in the Theme Developer Handbook.
 *
 * @since 1.5.0
 *
 * @see is_page()
 * @see is_single()
 * @global WP_Query $wp_query WordPress Query object.
 *
 * @param string|string[] $post_types Optional. Post type or array of post types
 *                                    to check against. Default empty.
 * @return bool Whether the query is for an existing single post
 *              or any of the given post types.
 */
function is_singular( $post_types = '' ) {
	global $wp_query;

	if ( ! isset( $wp_query ) ) {
		_doing_it_wrong( __FUNCTION__, __( 'Conditional query tags do not work before the query is run. Before then, they always return false.' ), '3.1.0' );
		return false;
	}

	return $wp_query->is_singular( $post_types );
}

/**
 * Determines whether the query is for a specific time.
 *
 * For more information on this and similar theme functions, check out
 * the {@link https://developer.wordpress.org/themes/basics/conditional-tags/
 * Conditional Tags} article in the Theme Developer Handbook.
 *
 * @since 1.5.0
 *
 * @global WP_Query $wp_query WordPress Query object.
 *
 * @return bool Whether the query is for a specific time.
 */
function is_time() {
	global $wp_query;

	if ( ! isset( $wp_query ) ) {
		_doing_it_wrong( __FUNCTION__, __( 'Conditional query tags do not work before the query is run. Before then, they always return false.' ), '3.1.0' );
		return false;
	}

	return $wp_query->is_time();
}

/**
 * Determines whether the query is for a trackback endpoint call.
 *
 * For more information on this and similar theme functions, check out
 * the {@link https://developer.wordpress.org/themes/basics/conditional-tags/
 * Conditional Tags} article in the Theme Developer Handbook.
 *
 * @since 1.5.0
 *
 * @global WP_Query $wp_query WordPress Query object.
 *
 * @return bool Whether the query is for a trackback endpoint call.
 */
function is_trackback() {
	global $wp_query;

	if ( ! isset( $wp_query ) ) {
		_doing_it_wrong( __FUNCTION__, __( 'Conditional query tags do not work before the query is run. Before then, they always return false.' ), '3.1.0' );
		return false;
	}

	return $wp_query->is_trackback();
}

/**
 * Determines whether the query is for an existing year archive.
 *
 * For more information on this and similar theme functions, check out
 * the {@link https://developer.wordpress.org/themes/basics/conditional-tags/
 * Conditional Tags} article in the Theme Developer Handbook.
 *
 * @since 1.5.0
 *
 * @global WP_Query $wp_query WordPress Query object.
 *
 * @return bool Whether the query is for an existing year archive.
 */
function is_year() {
	global $wp_query;

	if ( ! isset( $wp_query ) ) {
		_doing_it_wrong( __FUNCTION__, __( 'Conditional query tags do not work before the query is run. Before then, they always return false.' ), '3.1.0' );
		return false;
	}

	return $wp_query->is_year();
}

/**
 * Determines whether the query has resulted in a 404 (returns no results).
 *
 * For more information on this and similar theme functions, check out
 * the {@link https://developer.wordpress.org/themes/basics/conditional-tags/
 * Conditional Tags} article in the Theme Developer Handbook.
 *
 * @since 1.5.0
 *
 * @global WP_Query $wp_query WordPress Query object.
 *
 * @return bool Whether the query is a 404 error.
 */
function is_404() {
	global $wp_query;

	if ( ! isset( $wp_query ) ) {
		_doing_it_wrong( __FUNCTION__, __( 'Conditional query tags do not work before the query is run. Before then, they always return false.' ), '3.1.0' );
		return false;
	}

	return $wp_query->is_404();
}

/**
 * Is the query for an embedded post?
 *
 * @since 4.4.0
 *
 * @global WP_Query $wp_query WordPress Query object.
 *
 * @return bool Whether the query is for an embedded post.
 */
function is_embed() {
	global $wp_query;

	if ( ! isset( $wp_query ) ) {
		_doing_it_wrong( __FUNCTION__, __( 'Conditional query tags do not work before the query is run. Before then, they always return false.' ), '3.1.0' );
		return false;
	}

	return $wp_query->is_embed();
}

/**
 * Determines whether the query is the main query.
 *
 * For more information on this and similar theme functions, check out
 * the {@link https://developer.wordpress.org/themes/basics/conditional-tags/
 * Conditional Tags} article in the Theme Developer Handbook.
 *
 * @since 3.3.0
 *
 * @global WP_Query $wp_query WordPress Query object.
 *
 * @return bool Whether the query is the main query.
 */
function is_main_query() {
	global $wp_query;

	if ( ! isset( $wp_query ) ) {
		_doing_it_wrong( __FUNCTION__, __( 'Conditional query tags do not work before the query is run. Before then, they always return false.' ), '6.1.0' );
		return false;
	}

	if ( 'pre_get_posts' === current_filter() ) {
		_doing_it_wrong(
			__FUNCTION__,
			sprintf(
				/* translators: 1: pre_get_posts, 2: WP_Query->is_main_query(), 3: is_main_query(), 4: Documentation URL. */
				__( 'In %1$s, use the %2$s method, not the %3$s function. See %4$s.' ),
				'<code>pre_get_posts</code>',
				'<code>WP_Query->is_main_query()</code>',
				'<code>is_main_query()</code>',
				__( 'https://developer.wordpress.org/reference/functions/is_main_query/' )
			),
			'3.7.0'
		);
	}

	return $wp_query->is_main_query();
}

/*
 * The Loop. Post loop control.
 */

/**
 * Determines whether current WordPress query has posts to loop over.
 *
 * @since 1.5.0
 *
 * @global WP_Query $wp_query WordPress Query object.
 *
 * @return bool True if posts are available, false if end of the loop.
 */
function have_posts() {
	global $wp_query;

	if ( ! isset( $wp_query ) ) {
		return false;
	}

	return $wp_query->have_posts();
}

/**
 * Determines whether the caller is in the Loop.
 *
 * For more information on this and similar theme functions, check out
 * the {@link https://developer.wordpress.org/themes/basics/conditional-tags/
 * Conditional Tags} article in the Theme Developer Handbook.
 *
 * @since 2.0.0
 *
 * @global WP_Query $wp_query WordPress Query object.
 *
 * @return bool True if caller is within loop, false if loop hasn't started or ended.
 */
function in_the_loop() {
	global $wp_query;

	if ( ! isset( $wp_query ) ) {
		return false;
	}

	return $wp_query->in_the_loop;
}

/**
 * Rewind the loop posts.
 *
 * @since 1.5.0
 *
 * @global WP_Query $wp_query WordPress Query object.
 */
function rewind_posts() {
	global $wp_query;

	if ( ! isset( $wp_query ) ) {
		return;
	}

	$wp_query->rewind_posts();
}

/**
 * Iterate the post index in the loop.
 *
 * @since 1.5.0
 *
 * @global WP_Query $wp_query WordPress Query object.
 */
function the_post() {
	global $wp_query;

	if ( ! isset( $wp_query ) ) {
		return;
	}

	$wp_query->the_post();
}

/*
 * Comments loop.
 */

/**
 * Determines whether current WordPress query has comments to loop over.
 *
 * @since 2.2.0
 *
 * @global WP_Query $wp_query WordPress Query object.
 *
 * @return bool True if comments are available, false if no more comments.
 */
function have_comments() {
	global $wp_query;

	if ( ! isset( $wp_query ) ) {
		return false;
	}

	return $wp_query->have_comments();
}

/**
 * Iterate comment index in the comment loop.
 *
 * @since 2.2.0
 *
 * @global WP_Query $wp_query WordPress Query object.
 */
function the_comment() {
	global $wp_query;

	if ( ! isset( $wp_query ) ) {
		return;
	}

	$wp_query->the_comment();
}

/**
 * Redirect old slugs to the correct permalink.
 *
 * Attempts to find the current slug from the past slugs.
 *
 * @since 2.1.0
 */
function wp_old_slug_redirect() {
	if ( is_404() && '' !== get_query_var( 'name' ) ) {
		// Guess the current post type based on the query vars.
		if ( get_query_var( 'post_type' ) ) {
			$post_type = get_query_var( 'post_type' );
		} elseif ( get_query_var( 'attachment' ) ) {
			$post_type = 'attachment';
		} elseif ( get_query_var( 'pagename' ) ) {
			$post_type = 'page';
		} else {
			$post_type = 'post';
		}

		if ( is_array( $post_type ) ) {
			if ( count( $post_type ) > 1 ) {
				return;
			}
			$post_type = reset( $post_type );
		}

		// Do not attempt redirect for hierarchical post types.
		if ( is_post_type_hierarchical( $post_type ) ) {
			return;
		}

		$id = _find_post_by_old_slug( $post_type );

		if ( ! $id ) {
			$id = _find_post_by_old_date( $post_type );
		}

		/**
		 * Filters the old slug redirect post ID.
		 *
		 * @since 4.9.3
		 *
		 * @param int $id The redirect post ID.
		 */
		$id = apply_filters( 'old_slug_redirect_post_id', $id );

		if ( ! $id ) {
			return;
		}

		$link = get_permalink( $id );

		if ( get_query_var( 'paged' ) > 1 ) {
			$link = user_trailingslashit( trailingslashit( $link ) . 'page/' . get_query_var( 'paged' ) );
		} elseif ( is_embed() ) {
			$link = user_trailingslashit( trailingslashit( $link ) . 'embed' );
		}

		/**
		 * Filters the old slug redirect URL.
		 *
		 * @since 4.4.0
		 *
		 * @param string $link The redirect URL.
		 */
		$link = apply_filters( 'old_slug_redirect_url', $link );

		if ( ! $link ) {
			return;
		}

		wp_redirect( $link, 301 ); // Permanent redirect.
		exit;
	}
}

/**
 * Find the post ID for redirecting an old slug.
 *
 * @since 4.9.3
 * @access private
 *
 * @see wp_old_slug_redirect()
 * @global wpdb $wpdb WordPress database abstraction object.
 *
 * @param string $post_type The current post type based on the query vars.
 * @return int The Post ID.
 */
function _find_post_by_old_slug( $post_type ) {
	global $wpdb;

	$query = $wpdb->prepare( "SELECT post_id FROM $wpdb->postmeta, $wpdb->posts WHERE ID = post_id AND post_type = %s AND meta_key = '_wp_old_slug' AND meta_value = %s", $post_type, get_query_var( 'name' ) );

	/*
	 * If year, monthnum, or day have been specified, make our query more precise
	 * just in case there are multiple identical _wp_old_slug values.
	 */
	if ( get_query_var( 'year' ) ) {
		$query .= $wpdb->prepare( ' AND YEAR(post_date) = %d', get_query_var( 'year' ) );
	}
	if ( get_query_var( 'monthnum' ) ) {
		$query .= $wpdb->prepare( ' AND MONTH(post_date) = %d', get_query_var( 'monthnum' ) );
	}
	if ( get_query_var( 'day' ) ) {
		$query .= $wpdb->prepare( ' AND DAYOFMONTH(post_date) = %d', get_query_var( 'day' ) );
	}

	$key          = md5( $query );
	$last_changed = wp_cache_get_last_changed( 'posts' );
	$cache_key    = "find_post_by_old_slug:$key:$last_changed";
	$cache        = wp_cache_get( $cache_key, 'post-queries' );
	if ( false !== $cache ) {
		$id = $cache;
	} else {
		$id = (int) $wpdb->get_var( $query );
		wp_cache_set( $cache_key, $id, 'post-queries' );
	}

	return $id;
}

/**
 * Find the post ID for redirecting an old date.
 *
 * @since 4.9.3
 * @access private
 *
 * @see wp_old_slug_redirect()
 * @global wpdb $wpdb WordPress database abstraction object.
 *
 * @param string $post_type The current post type based on the query vars.
 * @return int The Post ID.
 */
function _find_post_by_old_date( $post_type ) {
	global $wpdb;

	$date_query = '';
	if ( get_query_var( 'year' ) ) {
		$date_query .= $wpdb->prepare( ' AND YEAR(pm_date.meta_value) = %d', get_query_var( 'year' ) );
	}
	if ( get_query_var( 'monthnum' ) ) {
		$date_query .= $wpdb->prepare( ' AND MONTH(pm_date.meta_value) = %d', get_query_var( 'monthnum' ) );
	}
	if ( get_query_var( 'day' ) ) {
		$date_query .= $wpdb->prepare( ' AND DAYOFMONTH(pm_date.meta_value) = %d', get_query_var( 'day' ) );
	}

	$id = 0;
	if ( $date_query ) {
		$query        = $wpdb->prepare( "SELECT post_id FROM $wpdb->postmeta AS pm_date, $wpdb->posts WHERE ID = post_id AND post_type = %s AND meta_key = '_wp_old_date' AND post_name = %s" . $date_query, $post_type, get_query_var( 'name' ) );
		$key          = md5( $query );
		$last_changed = wp_cache_get_last_changed( 'posts' );
		$cache_key    = "find_post_by_old_date:$key:$last_changed";
		$cache        = wp_cache_get( $cache_key, 'post-queries' );
		if ( false !== $cache ) {
			$id = $cache;
		} else {
			$id = (int) $wpdb->get_var( $query );
			if ( ! $id ) {
				// Check to see if an old slug matches the old date.
				$id = (int) $wpdb->get_var( $wpdb->prepare( "SELECT ID FROM $wpdb->posts, $wpdb->postmeta AS pm_slug, $wpdb->postmeta AS pm_date WHERE ID = pm_slug.post_id AND ID = pm_date.post_id AND post_type = %s AND pm_slug.meta_key = '_wp_old_slug' AND pm_slug.meta_value = %s AND pm_date.meta_key = '_wp_old_date'" . $date_query, $post_type, get_query_var( 'name' ) ) );
			}
			wp_cache_set( $cache_key, $id, 'post-queries' );
		}
	}

	return $id;
}

/**
 * Set up global post data.
 *
 * @since 1.5.0
 * @since 4.4.0 Added the ability to pass a post ID to `$post`.
 *
 * @global WP_Query $wp_query WordPress Query object.
 *
 * @param WP_Post|object|int $post WP_Post instance or Post ID/object.
 * @return bool True when finished.
 */
function setup_postdata( $post ) {
	global $wp_query;

	if ( ! empty( $wp_query ) && $wp_query instanceof WP_Query ) {
		return $wp_query->setup_postdata( $post );
	}

	return false;
}

/**
 * Generates post data.
 *
 * @since 5.2.0
 *
 * @global WP_Query $wp_query WordPress Query object.
 *
 * @param WP_Post|object|int $post WP_Post instance or Post ID/object.
 * @return array|false Elements of post, or false on failure.
 */
function generate_postdata( $post ) {
	global $wp_query;

	if ( ! empty( $wp_query ) && $wp_query instanceof WP_Query ) {
		return $wp_query->generate_postdata( $post );
	}

	return false;
}
iven request has access to update a specific item.
	 *
	 * @since 4.7.0
	 *
	 * @param WP_REST_Request $request Full details about the request.
	 * @return true|WP_Error True if the request has access to update the item, WP_Error object otherwise.
	 */
	public function update_item_permissions_check( $request ) {
		return new WP_Error(
			'invalid-method',
			/* translators: %s: Method name. */
			sprintf( __( "Method '%s' not implemented. Must be overridden in subclass." ), __METHOD__ ),
			array( 'status' => 405 )
		);
	}

	/**
	 * Updates one item from the collection.
	 *
	 * @since 4.7.0
	 *
	 * @param WP_REST_Request $request Full details about the request.
	 * @return WP_REST_Response|WP_Error Response object on success, or WP_Error object on failure.
	 */
	public function update_item( $request ) {
		return new WP_Error(
			'invalid-method',
			/* translators: %s: Method name. */
			sprintf( __( "Method '%s' not implemented. Must be overridden in subclass." ), __METHOD__ ),
			array( 'status' => 405 )
		);
	}

	/**
	 * Checks if a given request has access to delete a specific item.
	 *
	 * @since 4.7.0
	 *
	 * @param WP_REST_Request $request Full details about the request.
	 * @return true|WP_Error True if the request has access to delete the item, WP_Error object otherwise.
	 */
	public function delete_item_permissions_check( $request ) {
		return new WP_Error(
			'invalid-method',
			/* translators: %s: Method name. */
			sprintf( __( "Method '%s' not implemented. Must be overridden in subclass." ), __METHOD__ ),
			array( 'status' => 405 )
		);
	}

	/**
	 * Deletes one item from the collection.
	 *
	 * @since 4.7.0
	 *
	 * @param WP_REST_Request $request Full details about the request.
	 * @return WP_REST_Response|WP_Error Response object on success, or WP_Error object on failure.
	 */
	public function delete_item( $request ) {
		return new WP_Error(
			'invalid-method',
			/* translators: %s: Method name. */
			sprintf( __( "Method '%s' not implemented. Must be overridden in subclass." ), __METHOD__ ),
			array( 'status' => 405 )
		);
	}

	/**
	 * Prepares one item for create or update operation.
	 *
	 * @since 4.7.0
	 *
	 * @param WP_REST_Request $request Request object.
	 * @return object|WP_Error The prepared item, or WP_Error object on failure.
	 */
	protected function prepare_item_for_database( $request ) {
		return new WP_Error(
			'invalid-method',
			/* translators: %s: Method name. */
			sprintf( __( "Method '%s' not implemented. Must be overridden in subclass." ), __METHOD__ ),
			array( 'status' => 405 )
		);
	}

	/**
	 * Prepares the item for the REST response.
	 *
	 * @since 4.7.0
	 *
	 * @param mixed           $item    WordPress representation of the item.
	 * @param WP_REST_Request $request Request object.
	 * @return WP_REST_Response|WP_Error Response object on success, or WP_Error object on failure.
	 */
	public function prepare_item_for_response( $item, $request ) {
		return new WP_Error(
			'invalid-method',
			/* translators: %s: Method name. */
			sprintf( __( "Method '%s' not implemented. Must be overridden in subclass." ), __METHOD__ ),
			array( 'status' => 405 )
		);
	}

	/**
	 * Prepares a response for insertion into a collection.
	 *
	 * @since 4.7.0
	 *
	 * @param WP_REST_Response $response Response object.
	 * @return array|mixed Response data, ready for insertion into collection data.
	 */
	public function prepare_response_for_collection( $response ) {
		if ( ! ( $response instanceof WP_REST_Response ) ) {
			return $response;
		}

		$data   = (array) $response->get_data();
		$server = rest_get_server();
		$links  = $server::get_compact_response_links( $response );

		if ( ! empty( $links ) ) {
			$data['_links'] = $links;
		}

		return $data;
	}

	/**
	 * Filters a response based on the context defined in the schema.
	 *
	 * @since 4.7.0
	 *
	 * @param array  $response_data Response data to filter.
	 * @param string $context       Context defined in the schema.
	 * @return array Filtered response.
	 */
	public function filter_response_by_context( $response_data, $context ) {

		$schema = $this->get_item_schema();

		return rest_filter_response_by_context( $response_data, $schema, $context );
	}

	/**
	 * Retrieves the item's schema, conforming to JSON Schema.
	 *
	 * @since 4.7.0
	 *
	 * @return array Item schema data.
	 */
	public function get_item_schema() {
		return $this->add_additional_fields_schema( array() );
	}

	/**
	 * Retrieves the item's schema for display / public consumption purposes.
	 *
	 * @since 4.7.0
	 *
	 * @return array Public item schema data.
	 */
	public function get_public_item_schema() {

		$schema = $this->get_item_schema();

		if ( ! empty( $schema['properties'] ) ) {
			foreach ( $schema['properties'] as &$property ) {
				unset( $property['arg_options'] );
			}
		}

		return $schema;
	}

	/**
	 * Retrieves the query params for the collections.
	 *
	 * @since 4.7.0
	 *
	 * @return array Query parameters for the collection.
	 */
	public function get_collection_params() {
		return array(
			'context'  => $this->get_context_param(),
			'page'     => array(
				'description'       => __( 'Current page of the collection.' ),
				'type'              => 'integer',
				'default'           => 1,
				'sanitize_callback' => 'absint',
				'validate_callback' => 'rest_validate_request_arg',
				'minimum'           => 1,
			),
			'per_page' => array(
				'description'       => __( 'Maximum number of items to be returned in result set.' ),
				'type'              => 'integer',
				'default'           => 10,
				'minimum'           => 1,
				'maximum'           => 100,
				'sanitize_callback' => 'absint',
				'validate_callback' => 'rest_validate_request_arg',
			),
			'search'   => array(
				'description'       => __( 'Limit results to those matching a string.' ),
				'type'              => 'string',
				'sanitize_callback' => 'sanitize_text_field',
				'validate_callback' => 'rest_validate_request_arg',
			),
		);
	}

	/**
	 * Retrieves the magical context param.
	 *
	 * Ensures consistent descriptions between endpoints, and populates enum from schema.
	 *
	 * @since 4.7.0
	 *
	 * @param array $args Optional. Additional arguments for context parameter. Default empty array.
	 * @return array Context parameter details.
	 */
	public function get_context_param( $args = array() ) {
		$param_details = array(
			'description'       => __( 'Scope under which the request is made; determines fields present in response.' ),
			'type'              => 'string',
			'sanitize_callback' => 'sanitize_key',
			'validate_callback' => 'rest_validate_request_arg',
		);

		$schema = $this->get_item_schema();

		if ( empty( $schema['properties'] ) ) {
			return array_merge( $param_details, $args );
		}

		$contexts = array();

		foreach ( $schema['properties'] as $attributes ) {
			if ( ! empty( $attributes['context'] ) ) {
				$contexts = array_merge( $contexts, $attributes['context'] );
			}
		}

		if ( ! empty( $contexts ) ) {
			$param_details['enum'] = array_unique( $contexts );
			rsort( $param_details['enum'] );
		}

		return array_merge( $param_details, $args );
	}

	/**
	 * Adds the values from additional fields to a data object.
	 *
	 * @since 4.7.0
	 *
	 * @param array           $response_data Prepared response array.
	 * @param WP_REST_Request $request       Full details about the request.
	 * @return array Modified data object with additional fields.
	 */
	protected function add_additional_fields_to_object( $response_data, $request ) {

		$additional_fields = $this->get_additional_fields();

		$requested_fields = $this->get_fields_for_response( $request );

		foreach ( $additional_fields as $field_name => $field_options ) {
			if ( ! $field_options['get_callback'] ) {
				continue;
			}

			if ( ! rest_is_field_included( $field_name, $requested_fields ) ) {
				continue;
			}

			$response_data[ $field_name ] = call_user_func(
				$field_options['get_callback'],
				$response_data,
				$field_name,
				$request,
				$this->get_object_type()
			);
		}

		return $response_data;
	}

	/**
	 * Updates the values of additional fields added to a data object.
	 *
	 * @since 4.7.0
	 *
	 * @param object          $data_object Data model like WP_Term or WP_Post.
	 * @param WP_REST_Request $request     Full details about the request.
	 * @return true|WP_Error True on success, WP_Error object if a field cannot be updated.
	 */
	protected function update_additional_fields_for_object( $data_object, $request ) {
		$additional_fields = $this->get_additional_fields();

		foreach ( $additional_fields as $field_name => $field_options ) {
			if ( ! $field_options['update_callback'] ) {
				continue;
			}

			// Don't run the update callbacks if the data wasn't passed in the request.
			if ( ! isset( $request[ $field_name ] ) ) {
				continue;
			}

			$result = call_user_func(
				$field_options['update_callback'],
				$request[ $field_name ],
				$data_object,
				$field_name,
				$request,
				$this->get_object_type()
			);

			if ( is_wp_error( $result ) ) {
				return $result;
			}
		}

		return true;
	}

	/**
	 * Adds the schema from additional fields to a schema array.
	 *
	 * The type of object is inferred from the passed schema.
	 *
	 * @since 4.7.0
	 *
	 * @param array $schema Schema array.
	 * @return array Modified Schema array.
	 */
	protected function add_additional_fields_schema( $schema ) {
		if ( empty( $schema['title'] ) ) {
			return $schema;
		}

		// Can't use $this->get_object_type otherwise we cause an inf loop.
		$object_type = $schema['title'];

		$additional_fields = $this->get_additional_fields( $object_type );

		foreach ( $additional_fields as $field_name => $field_options ) {
			if ( ! $field_options['schema'] ) {
				continue;
			}

			$schema['properties'][ $field_name ] = $field_options['schema'];
		}

		return $schema;
	}

	/**
	 * Retrieves all of the registered additional fields for a given object-type.
	 *
	 * @since 4.7.0
	 *
	 * @global array $wp_rest_additional_fields Holds registered fields, organized by object type.
	 *
	 * @param string $object_type Optional. The object type.
	 * @return array Registered additional fields (if any), empty array if none or if the object type
	 *               could not be inferred.
	 */
	protected function get_additional_fields( $object_type = null ) {
		global $wp_rest_additional_fields;

		if ( ! $object_type ) {
			$object_type = $this->get_object_type();
		}

		if ( ! $object_type ) {
			return array();
		}

		if ( ! $wp_rest_additional_fields || ! isset( $wp_rest_additional_fields[ $object_type ] ) ) {
			return array();
		}

		return $wp_rest_additional_fields[ $object_type ];
	}

	/**
	 * Retrieves the object type this controller is responsible for managing.
	 *
	 * @since 4.7.0
	 *
	 * @return string Object type for the controller.
	 */
	protected function get_object_type() {
		$schema = $this->get_item_schema();

		if ( ! $schema || ! isset( $schema['title'] ) ) {
			return null;
		}

		return $schema['title'];
	}

	/**
	 * Gets an array of fields to be included on the response.
	 *
	 * Included fields are based on item schema and `_fields=` request argument.
	 *
	 * @since 4.9.6
	 *
	 * @param WP_REST_Request $request Full details about the request.
	 * @return string[] Fields to be included in the response.
	 */
	public function get_fields_for_response( $request ) {
		$schema     = $this->get_item_schema();
		$properties = isset( $schema['properties'] ) ? $schema['properties'] : array();

		$additional_fields = $this->get_additional_fields();

		foreach ( $additional_fields as $field_name => $field_options ) {
			/*
			 * For back-compat, include any field with an empty schema
			 * because it won't be present in $this->get_item_schema().
			 */
			if ( is_null( $field_options['schema'] ) ) {
				$properties[ $field_name ] = $field_options;
			}
		}

		// Exclude fields that specify a different context than the request context.
		$context = $request['context'];
		if ( $context ) {
			foreach ( $properties as $name => $options ) {
				if ( ! empty( $options['context'] ) && ! in_array( $context, $options['context'], true ) ) {
					unset( $properties[ $name ] );
				}
			}
		}

		$fields = array_keys( $properties );

		/*
		 * '_links' and '_embedded' are not typically part of the item schema,
		 * but they can be specified in '_fields', so they are added here as a
		 * convenience for checking with rest_is_field_included().
		 */
		$fields[] = '_links';
		if ( $request->has_param( '_embed' ) ) {
			$fields[] = '_embedded';
		}

		$fields = array_unique( $fields );

		if ( ! isset( $request['_fields'] ) ) {
			return $fields;
		}
		$requested_fields = wp_parse_list( $request['_fields'] );
		if ( 0 === count( $requested_fields ) ) {
			return $fields;
		}
		// Trim off outside whitespace from the comma delimited list.
		$requested_fields = array_map( 'trim', $requested_fields );
		// Always persist 'id', because it can be needed for add_additional_fields_to_object().
		if ( in_array( 'id', $fields, true ) ) {
			$requested_fields[] = 'id';
		}
		// Return the list of all requested fields which appear in the schema.
		return array_reduce(
			$requested_fields,
			static function( $response_fields, $field ) use ( $fields ) {
				if ( in_array( $field, $fields, true ) ) {
					$response_fields[] = $field;
					return $response_fields;
				}
				// Check for nested fields if $field is not a direct match.
				$nested_fields = explode( '.', $field );
				/*
				 * A nested field is included so long as its top-level property
				 * is present in the schema.
				 */
				if ( in_array( $nested_fields[0], $fields, true ) ) {
					$response_fields[] = $field;
				}
				return $response_fields;
			},
			array()
		);
	}

	/**
	 * Retrieves an array of endpoint arguments from the item schema for the controller.
	 *
	 * @since 4.7.0
	 *
	 * @param string $method Optional. HTTP method of the request. The arguments for `CREATABLE` requests are
	 *                       checked for required values and may fall-back to a given default, this is not done
	 *                       on `EDITABLE` requests. Default WP_REST_Server::CREATABLE.
	 * @return array Endpoint arguments.
	 */
	public function get_endpoint_args_for_item_schema( $method = WP_REST_Server::CREATABLE ) {
		return rest_get_endpoint_args_for_schema( $this->get_item_schema(), $method );
	}

	/**
	 * Sanitizes the slug value.
	 *
	 * @since 4.7.0
	 *
	 * @internal We can't use sanitize_title() directly, as the second
	 * parameter is the fallback title, which would end up being set to the
	 * request object.
	 *
	 * @see https://github.com/WP-API/WP-API/issues/1585
	 *
	 * @todo Remove this in favour of https://core.trac.wordpress.org/ticket/34659
	 *
	 * @param string $slug Slug value passed in request.
	 * @return string Sanitized value for the slug.
	 */
	public function sanitize_slug( $slug ) {
		return sanitize_title( $slug );
	}
}