<?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
     * @access public
     * @var array
     */
    public $callbacks = array();

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

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

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

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

    /**
     * Hooks a function or method to a specific filter action.
     *
     * @since 4.7.0
     * @access public
     *
     * @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 reseting callback priority keys mid-iteration.
     *
     * @since 4.7.0
     * @access private
     *
     * @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
     * @access public
     *
     * @param string   $tag                The filter hook to which the function to be removed is hooked. Used
     *                                     for building the callback ID when SPL is not available.
     * @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
     * @access public
     *
     * @param callable|bool $function_to_check Optional. The callback to check for. Default false.
     * @param string        $tag               Optional. The name of the filter hook. Used for building
     *                                         the callback ID when SPL is not available. Default empty.
     * @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
     * @access public
     *
     * @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
     * @access public
     *
     * @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();
        } else if ( isset( $this->callbacks[ $priority ] ) ) {
            unset( $this->callbacks[ $priority ] );
        }

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

    /**
     * Calls the callback functions added to a filter hook.
     *
     * @since 4.7.0
     * @access public
     *
     * @param mixed $value The value to filter.
     * @param array $args  Arguments to pass to callbacks.
     * @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 ] = $priority = current( $this->iterations[ $nesting_level ] );

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

                // Avoid the array_slice if possible.
                if ( $the_['accepted_args'] == 0 ) {
                    $value = call_user_func_array( $the_['function'], array() );
                } 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;
    }

    /**
     * Executes the callback functions hooked on a specific action hook.
     *
     * @since 4.7.0
     * @access public
     *
     * @param mixed $args Arguments to pass to the hook callbacks.
     */
    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
     * @access public
     *
     * @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
     * @access public
     *
     * @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
     * @access public
     * @static
     *
     * @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
     * @access public
     *
     * @link http://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
     * @access public
     *
     * @link http://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
     * @access public
     *
     * @link http://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
     * @access public
     *
     * @link http://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
     * @access public
     *
     * @link http://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
     * @access public
     *
     * @link http://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
     * @access public
     *
     * @link http://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
     * @access public
     *
     * @link http://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
     * @access public
     *
     * @link http://php.net/manual/en/iterator.rewind.php
     */
    public function rewind() {
        reset( $this->callbacks );
    }

}