source: tags/5.4/src/wp-includes/class-wp-hook.php

<?php
/**
 * Plugin API: WP_Hook class
 *
 * @package WordPress
 * @subpackage Plugin
 * @since 4.7.0
 */

/**
 * Core class used to implement action and filter hook functionality.
 *
 * @since 4.7.0
 *
 * @see Iterator
 * @see ArrayAccess
 */
final class WP_Hook implements Iterator, ArrayAccess {

        /**
         * Hook callbacks.
         *
         * @since 4.7.0
         * @var array
         */
        public $callbacks = array();

        /**
         * The priority keys of actively running iterations of a hook.
         *
         * @since 4.7.0
         * @var array
         */
        private $iterations = array();

        /**
         * The current priority of actively running iterations of a hook.
         *
         * @since 4.7.0
         * @var array
         */
        private $current_priority = array();

        /**
         * Number of levels this hook can be recursively called.
         *
         * @since 4.7.0
         * @var int
         */
        private $nesting_level = 0;

        /**
         * Flag for if we're current doing an action, rather than a filter.
         *
         * @since 4.7.0
         * @var bool
         */
        private $doing_action = false;

        /**
         * Hooks a function or method to a specific filter action.
         *
         * @since 4.7.0
         *
         * @param string   $tag             The name of the filter to hook the $function_to_add callback to.
         * @param callable $function_to_add The callback to be run when the filter is applied.
         * @param int      $priority        The order in which the functions associated with a particular action
         *                                  are executed. Lower numbers correspond with earlier execution,
         *                                  and functions with the same priority are executed in the order
         *                                  in which they were added to the action.
         * @param int      $accepted_args   The number of arguments the function accepts.
         */
        public function add_filter( $tag, $function_to_add, $priority, $accepted_args ) {
                $idx = _wp_filter_build_unique_id( $tag, $function_to_add, $priority );

                $priority_existed = isset( $this->callbacks[ $priority ] );

                $this->callbacks[ $priority ][ $idx ] = array(
                        'function'      => $function_to_add,
                        'accepted_args' => $accepted_args,
                );

                // If we're adding a new priority to the list, put them back in sorted order.
                if ( ! $priority_existed && count( $this->callbacks ) > 1 ) {
                        ksort( $this->callbacks, SORT_NUMERIC );
                }

                if ( $this->nesting_level > 0 ) {
                        $this->resort_active_iterations( $priority, $priority_existed );
                }
        }

        /**
         * Handles resetting callback priority keys mid-iteration.
         *
         * @since 4.7.0
         *
         * @param bool|int $new_priority     Optional. The priority of the new filter being added. Default false,
         *                                   for no priority being added.
         * @param bool     $priority_existed Optional. Flag for whether the priority already existed before the new
         *                                   filter was added. Default false.
         */
        private function resort_active_iterations( $new_priority = false, $priority_existed = false ) {
                $new_priorities = array_keys( $this->callbacks );

                // If there are no remaining hooks, clear out all running iterations.
                if ( ! $new_priorities ) {
                        foreach ( $this->iterations as $index => $iteration ) {
                                $this->iterations[ $index ] = $new_priorities;
                        }
                        return;
                }

                $min = min( $new_priorities );
                foreach ( $this->iterations as $index => &$iteration ) {
                        $current = current( $iteration );
                        // If we're already at the end of this iteration, just leave the array pointer where it is.
                        if ( false === $current ) {
                                continue;
                        }

                        $iteration = $new_priorities;

                        if ( $current < $min ) {
                                array_unshift( $iteration, $current );
                                continue;
                        }

                        while ( current( $iteration ) < $current ) {
                                if ( false === next( $iteration ) ) {
                                        break;
                                }
                        }

                        // If we have a new priority that didn't exist, but ::apply_filters() or ::do_action() thinks it's the current priority...
                        if ( $new_priority === $this->current_priority[ $index ] && ! $priority_existed ) {
                                /*
                                 * ...and the new priority is the same as what $this->iterations thinks is the previous
                                 * priority, we need to move back to it.
                                 */

                                if ( false === current( $iteration ) ) {
                                        // If we've already moved off the end of the array, go back to the last element.
                                        $prev = end( $iteration );
                                } else {
                                        // Otherwise, just go back to the previous element.
                                        $prev = prev( $iteration );
                                }
                                if ( false === $prev ) {
                                        // Start of the array. Reset, and go about our day.
                                        reset( $iteration );
                                } elseif ( $new_priority !== $prev ) {
                                        // Previous wasn't the same. Move forward again.
                                        next( $iteration );
                                }
                        }
                }
                unset( $iteration );
        }

        /**
         * Unhooks a function or method from a specific filter action.
         *
         * @since 4.7.0
         *
         * @param string   $tag                The filter hook to which the function to be removed is hooked.
         * @param callable $function_to_remove The callback to be removed from running when the filter is applied.
         * @param int      $priority           The exact priority used when adding the original filter callback.
         * @return bool Whether the callback existed before it was removed.
         */
        public function remove_filter( $tag, $function_to_remove, $priority ) {
                $function_key = _wp_filter_build_unique_id( $tag, $function_to_remove, $priority );

                $exists = isset( $this->callbacks[ $priority ][ $function_key ] );
                if ( $exists ) {
                        unset( $this->callbacks[ $priority ][ $function_key ] );
                        if ( ! $this->callbacks[ $priority ] ) {
                                unset( $this->callbacks[ $priority ] );
                                if ( $this->nesting_level > 0 ) {
                                        $this->resort_active_iterations();
                                }
                        }
                }
                return $exists;
        }

        /**
         * Checks if a specific action has been registered for this hook.
         *
         * @since 4.7.0
         *
         * @param string        $tag               Optional. The name of the filter hook. Default empty.
         * @param callable|bool $function_to_check Optional. The callback to check for. Default false.
         * @return bool|int The priority of that hook is returned, or false if the function is not attached.
         */
        public function has_filter( $tag = '', $function_to_check = false ) {
                if ( false === $function_to_check ) {
                        return $this->has_filters();
                }

                $function_key = _wp_filter_build_unique_id( $tag, $function_to_check, false );
                if ( ! $function_key ) {
                        return false;
                }

                foreach ( $this->callbacks as $priority => $callbacks ) {
                        if ( isset( $callbacks[ $function_key ] ) ) {
                                return $priority;
                        }
                }

                return false;
        }

        /**
         * Checks if any callbacks have been registered for this hook.
         *
         * @since 4.7.0
         *
         * @return bool True if callbacks have been registered for the current hook, otherwise false.
         */
        public function has_filters() {
                foreach ( $this->callbacks as $callbacks ) {
                        if ( $callbacks ) {
                                return true;
                        }
                }
                return false;
        }

        /**
         * Removes all callbacks from the current filter.
         *
         * @since 4.7.0
         *
         * @param int|bool $priority Optional. The priority number to remove. Default false.
         */
        public function remove_all_filters( $priority = false ) {
                if ( ! $this->callbacks ) {
                        return;
                }

                if ( false === $priority ) {
                        $this->callbacks = array();
                } elseif ( isset( $this->callbacks[ $priority ] ) ) {
                        unset( $this->callbacks[ $priority ] );
                }

                if ( $this->nesting_level > 0 ) {
                        $this->resort_active_iterations();
                }
        }

        /**
         * Calls the callback functions that have been added to a filter hook.
         *
         * @since 4.7.0
         *
         * @param mixed $value The value to filter.
         * @param array $args  Additional parameters to pass to the callback functions.
         *                     This array is expected to include $value at index 0.
         * @return mixed The filtered value after all hooked functions are applied to it.
         */
        public function apply_filters( $value, $args ) {
                if ( ! $this->callbacks ) {
                        return $value;
                }

                $nesting_level = $this->nesting_level++;

                $this->iterations[ $nesting_level ] = array_keys( $this->callbacks );
                $num_args                           = count( $args );

                do {
                        $this->current_priority[ $nesting_level ] = current( $this->iterations[ $nesting_level ] );
                        $priority                                 = $this->current_priority[ $nesting_level ];

                        foreach ( $this->callbacks[ $priority ] as $the_ ) {
                                if ( ! $this->doing_action ) {
                                        $args[0] = $value;
                                }

                                // Avoid the array_slice() if possible.
                                if ( 0 == $the_['accepted_args'] ) {
                                        $value = call_user_func( $the_['function'] );
                                } elseif ( $the_['accepted_args'] >= $num_args ) {
                                        $value = call_user_func_array( $the_['function'], $args );
                                } else {
                                        $value = call_user_func_array( $the_['function'], array_slice( $args, 0, (int) $the_['accepted_args'] ) );
                                }
                        }
                } while ( false !== next( $this->iterations[ $nesting_level ] ) );

                unset( $this->iterations[ $nesting_level ] );
                unset( $this->current_priority[ $nesting_level ] );

                $this->nesting_level--;

                return $value;
        }

        /**
         * Calls the callback functions that have been added to an action hook.
         *
         * @since 4.7.0
         *
         * @param array $args Parameters to pass to the callback functions.
         */
        public function do_action( $args ) {
                $this->doing_action = true;
                $this->apply_filters( '', $args );

                // If there are recursive calls to the current action, we haven't finished it until we get to the last one.
                if ( ! $this->nesting_level ) {
                        $this->doing_action = false;
                }
        }

        /**
         * Processes the functions hooked into the 'all' hook.
         *
         * @since 4.7.0
         *
         * @param array $args Arguments to pass to the hook callbacks. Passed by reference.
         */
        public function do_all_hook( &$args ) {
                $nesting_level                      = $this->nesting_level++;
                $this->iterations[ $nesting_level ] = array_keys( $this->callbacks );

                do {
                        $priority = current( $this->iterations[ $nesting_level ] );
                        foreach ( $this->callbacks[ $priority ] as $the_ ) {
                                call_user_func_array( $the_['function'], $args );
                        }
                } while ( false !== next( $this->iterations[ $nesting_level ] ) );

                unset( $this->iterations[ $nesting_level ] );
                $this->nesting_level--;
        }

        /**
         * Return the current priority level of the currently running iteration of the hook.
         *
         * @since 4.7.0
         *
         * @return int|false If the hook is running, return the current priority level. If it isn't running, return false.
         */
        public function current_priority() {
                if ( false === current( $this->iterations ) ) {
                        return false;
                }

                return current( current( $this->iterations ) );
        }

        /**
         * Normalizes filters set up before WordPress has initialized to WP_Hook objects.
         *
         * @since 4.7.0
         *
         * @param array $filters Filters to normalize.
         * @return WP_Hook[] Array of normalized filters.
         */
        public static function build_preinitialized_hooks( $filters ) {
                /** @var WP_Hook[] $normalized */
                $normalized = array();

                foreach ( $filters as $tag => $callback_groups ) {
                        if ( is_object( $callback_groups ) && $callback_groups instanceof WP_Hook ) {
                                $normalized[ $tag ] = $callback_groups;
                                continue;
                        }
                        $hook = new WP_Hook();

                        // Loop through callback groups.
                        foreach ( $callback_groups as $priority => $callbacks ) {

                                // Loop through callbacks.
                                foreach ( $callbacks as $cb ) {
                                        $hook->add_filter( $tag, $cb['function'], $priority, $cb['accepted_args'] );
                                }
                        }
                        $normalized[ $tag ] = $hook;
                }
                return $normalized;
        }

        /**
         * Determines whether an offset value exists.
         *
         * @since 4.7.0
         *
         * @link https://www.php.net/manual/en/arrayaccess.offsetexists.php
         *
         * @param mixed $offset An offset to check for.
         * @return bool True if the offset exists, false otherwise.
         */
        public function offsetExists( $offset ) {
                return isset( $this->callbacks[ $offset ] );
        }

        /**
         * Retrieves a value at a specified offset.
         *
         * @since 4.7.0
         *
         * @link https://www.php.net/manual/en/arrayaccess.offsetget.php
         *
         * @param mixed $offset The offset to retrieve.
         * @return mixed If set, the value at the specified offset, null otherwise.
         */
        public function offsetGet( $offset ) {
                return isset( $this->callbacks[ $offset ] ) ? $this->callbacks[ $offset ] : null;
        }

        /**
         * Sets a value at a specified offset.
         *
         * @since 4.7.0
         *
         * @link https://www.php.net/manual/en/arrayaccess.offsetset.php
         *
         * @param mixed $offset The offset to assign the value to.
         * @param mixed $value The value to set.
         */
        public function offsetSet( $offset, $value ) {
                if ( is_null( $offset ) ) {
                        $this->callbacks[] = $value;
                } else {
                        $this->callbacks[ $offset ] = $value;
                }
        }

        /**
         * Unsets a specified offset.
         *
         * @since 4.7.0
         *
         * @link https://www.php.net/manual/en/arrayaccess.offsetunset.php
         *
         * @param mixed $offset The offset to unset.
         */
        public function offsetUnset( $offset ) {
                unset( $this->callbacks[ $offset ] );
        }

        /**
         * Returns the current element.
         *
         * @since 4.7.0
         *
         * @link https://www.php.net/manual/en/iterator.current.php
         *
         * @return array Of callbacks at current priority.
         */
        public function current() {
                return current( $this->callbacks );
        }

        /**
         * Moves forward to the next element.
         *
         * @since 4.7.0
         *
         * @link https://www.php.net/manual/en/iterator.next.php
         *
         * @return array Of callbacks at next priority.
         */
        public function next() {
                return next( $this->callbacks );
        }

        /**
         * Returns the key of the current element.
         *
         * @since 4.7.0
         *
         * @link https://www.php.net/manual/en/iterator.key.php
         *
         * @return mixed Returns current priority on success, or NULL on failure
         */
        public function key() {
                return key( $this->callbacks );
        }

        /**
         * Checks if current position is valid.
         *
         * @since 4.7.0
         *
         * @link https://www.php.net/manual/en/iterator.valid.php
         *
         * @return boolean
         */
        public function valid() {
                return key( $this->callbacks ) !== null;
        }

        /**
         * Rewinds the Iterator to the first element.
         *
         * @since 4.7.0
         *
         * @link https://www.php.net/manual/en/iterator.rewind.php
         */
        public function rewind() {
                reset( $this->callbacks );
        }

}