First events code

Add the basic code for adding events.

diff --git a/lib/event.php b/lib/event.php
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+++ b/lib/event.php
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+<?php
+/**
+ * Laconica, the distributed open-source microblogging tool
+ *
+ * utilities for defining and running event handlers
+ *
+ * PHP version 5
+ *
+ * LICENCE: This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * @category  Event
+ * @package   Laconica
+ * @author    Evan Prodromou <evan@controlyourself.ca>
+ * @copyright 2008 Control Yourself, Inc.
+ * @license   http://www.fsf.org/licensing/licenses/agpl-3.0.html GNU Affero General Public License version 3.0
+ * @link      http://laconi.ca/
+ */
+
+if (!defined('LACONICA')) {
+    exit(1);
+}
+
+/**
+ * Class for events
+ *
+ * This "class" two static functions for managing events in the Laconica code.
+ *
+ * @category Event
+ * @package  Laconica
+ * @author   Evan Prodromou <evan@controlyourself.ca>
+ * @license  http://www.fsf.org/licensing/licenses/agpl-3.0.html GNU Affero General Public License version 3.0
+ * @link     http://laconi.ca/
+ *
+ * @todo     Define a system for using Event instances
+ */
+
+class Event {
+
+    /* Global array of hooks, mapping eventname => array of callables */
+
+    protected static $_handlers = array();
+
+    /**
+     * Add an event handler
+     *
+     * To run some code at a particular point in Laconica processing.
+     * Named events include receiving an XMPP message, adding a new notice,
+     * or showing part of an HTML page.
+     *
+     * The arguments to the handler vary by the event. Handlers can return
+     * two possible values: false means that the event has been replaced by
+     * the handler completely, and no default processing should be done.
+     * Non-false means successful handling, and that the default processing
+     * should succeed. (Note that this only makes sense for some events.)
+     *
+     * Handlers can also abort processing by throwing an exception; these will
+     * be caught by the closest code and displayed as errors.
+     *
+     * @param string   $name    Name of the event
+     * @param callable $handler Code to run
+     *
+     * @return void
+     */
+
+    public static function addHandler($name, $handler) {
+        if (array_key_exists($name, Event::$_handlers)) {
+            Event::$_handlers[$name][] = $handler;
+        } else {
+            Event::$_handlers[$name] = array($handler);
+        }
+    }
+
+    /**
+     * Handle an event
+     *
+     * Events are any point in the code that we want to expose for admins
+     * or third-party developers to use.
+     *
+     * We pass in an array of arguments (including references, for stuff
+     * that can be changed), and each assigned handler gets run with those
+     * arguments. Exceptions can be thrown to indicate an error.
+     *
+     * @param string $name Name of the event that's happening
+     * @param array  $args Arguments for handlers
+     *
+     * @return boolean flag saying whether to continue processing, based
+     *                 on results of handlers.
+     */
+
+    public static function handle($name, $args) {
+        $result = null;
+        if (array_key_exists($name, Event::$_handlers)) {
+            foreach (Event::$_handlers[$name] as $handler) {
+                $result = call_user_func_array($handler, $args);
+                if ($result === false) {
+                    break;
+                }
+            }
+        }
+        return ($result === false);
+    }
+}