<?php

/**
 * @package KantPHP
 * @author  Zhenqiang Zhang <zhenqiang.zhang@hotmail.com>
 * @copyright (c) KantPHP Studio, All rights reserved.
 * @license http://www.opensource.org/licenses/BSD-3-Clause  The BSD 3-Clause License
 */
namespace Kant\Foundation;

/**
 * Event is the base class for all event classes.
 *
 * It encapsulates the parameters associated with an event.
 * The [[sender]] property describes who raises the event.
 * And the [[handled]] property indicates if the event is handled.
 * If an event handler sets [[handled]] to be true, the rest of the
 * uninvoked handlers will no longer be called to handle the event.
 *
 * Additionally, when attaching an event handler, extra data may be passed
 * and be available via the [[data]] property when the event handler is invoked.
 *
 * @author Qiang Xue <qiang.xue@gmail.com>
 * @since 2.0
 */
class Event extends BaseObject
{

    /**
     *
     * @var string the event name. This property is set by [[Component::trigger()]] and [[trigger()]].
     *      Event handlers may use this property to check what event it is handling.
     */
    public $name;

    /**
     *
     * @var object the sender of this event. If not set, this property will be
     *      set as the object whose "trigger()" method is called.
     *      This property may also be a `null` when this event is a
     *      class-level event which is triggered in a static context.
     */
    public $sender;

    /**
     *
     * @var boolean whether the event is handled. Defaults to false.
     *      When a handler sets this to be true, the event processing will stop and
     *      ignore the rest of the uninvoked event handlers.
     */
    public $handled = false;

    /**
     *
     * @var mixed the data that is passed to [[Component::on()]] when attaching an event handler.
     *      Note that this varies according to which event handler is currently executing.
     */
    public $data;

    /**
     *
     * @var array contains all globally registered event handlers.
     */
    private static $_events = [];

    /**
     * Attaches an event handler to a class-level event.
     *
     * When a class-level event is triggered, event handlers attached
     * to that class and all parent classes will be invoked.
     *
     * For example, the following code attaches an event handler to `ActiveRecord`'s
     * `afterInsert` event:
     *
     * ```php
     * Event::on(ActiveRecord::className(), ActiveRecord::EVENT_AFTER_INSERT, function ($event) {
     * Kant::trace(get_class($event->sender) . ' is inserted.');
     * });
     * ```
     *
     * The handler will be invoked for EVERY successful ActiveRecord insertion.
     *
     * For more details about how to declare an event handler, please refer to [[Component::on()]].
     *
     * @param string $class
     *            the fully qualified class name to which the event handler needs to attach.
     * @param string $name
     *            the event name.
     * @param callable $handler
     *            the event handler.
     * @param mixed $data
     *            the data to be passed to the event handler when the event is triggered.
     *            When the event handler is invoked, this data can be accessed via [[Event::data]].
     * @param boolean $append
     *            whether to append new event handler to the end of the existing
     *            handler list. If false, the new handler will be inserted at the beginning of the existing
     *            handler list.
     * @see off()
     */
    public static function on($class, $name, $handler, $data = null, $append = true)
    {
        $class = ltrim($class, '\\');
        if ($append || empty(self::$_events[$name][$class])) {
            self::$_events[$name][$class][] = [
                $handler,
                $data
            ];
        } else {
            array_unshift(self::$_events[$name][$class], [
                $handler,
                $data
            ]);
        }
    }

    /**
     * Detaches an event handler from a class-level event.
     *
     * This method is the opposite of [[on()]].
     *
     * @param string $class
     *            the fully qualified class name from which the event handler needs to be detached.
     * @param string $name
     *            the event name.
     * @param callable $handler
     *            the event handler to be removed.
     *            If it is null, all handlers attached to the named event will be removed.
     * @return boolean whether a handler is found and detached.
     * @see on()
     */
    public static function off($class, $name, $handler = null)
    {
        $class = ltrim($class, '\\');
        if (empty(self::$_events[$name][$class])) {
            return false;
        }
        if ($handler === null) {
            unset(self::$_events[$name][$class]);
            return true;
        } else {
            $removed = false;
            foreach (self::$_events[$name][$class] as $i => $event) {
                if ($event[0] === $handler) {
                    unset(self::$_events[$name][$class][$i]);
                    $removed = true;
                }
            }
            if ($removed) {
                self::$_events[$name][$class] = array_values(self::$_events[$name][$class]);
            }
            
            return $removed;
        }
    }

    /**
     * Returns a value indicating whether there is any handler attached to the specified class-level event.
     * Note that this method will also check all parent classes to see if there is any handler attached
     * to the named event.
     * 
     * @param string|object $class
     *            the object or the fully qualified class name specifying the class-level event.
     * @param string $name
     *            the event name.
     * @return boolean whether there is any handler attached to the event.
     */
    public static function hasHandlers($class, $name)
    {
        if (empty(self::$_events[$name])) {
            return false;
        }
        if (is_object($class)) {
            $class = get_class($class);
        } else {
            $class = ltrim($class, '\\');
        }
        
        $classes = array_merge([
            $class
        ], class_parents($class, true), class_implements($class, true));
        
        foreach ($classes as $class) {
            if (!empty(self::$_events[$name][$class])) {
                return true;
            }
        }
        
        return false;
    }

    /**
     * Triggers a class-level event.
     * This method will cause invocation of event handlers that are attached to the named event
     * for the specified class and all its parent classes.
     * 
     * @param string|object $class
     *            the object or the fully qualified class name specifying the class-level event.
     * @param string $name
     *            the event name.
     * @param Event $event
     *            the event parameter. If not set, a default [[Event]] object will be created.
     */
    public static function trigger($class, $name, $event = null)
    {
        if (empty(self::$_events[$name])) {
            return;
        }
        if ($event === null) {
            $event = new static();
        }
        $event->handled = false;
        $event->name = $name;
        
        if (is_object($class)) {
            if ($event->sender === null) {
                $event->sender = $class;
            }
            $class = get_class($class);
        } else {
            $class = ltrim($class, '\\');
        }
        
        $classes = array_merge([
            $class
        ], class_parents($class, true), class_implements($class, true));
        
        foreach ($classes as $class) {
            if (!empty(self::$_events[$name][$class])) {
                foreach (self::$_events[$name][$class] as $handler) {
                    $event->data = $handler[1];
                    call_user_func($handler[0], $event);
                    if ($event->handled) {
                        return;
                    }
                }
            }
        }
    }
}
