EventEmitter: just Evenement plus emitOnce and...

...optional event name validation

composer.json

@@ -13,5 +13,9 @@
         "psr-4": {
             "ipl\\Tests\\Stdlib\\": "tests/php"
         }
-    }
+    },
+  "require": {
+    "php": ">=5.4.0",
+    "evenement/evenement": "^2"
+  }
 }

src/EventEmitter.php

@@ -0,0 +1,57 @@
+<?php
+
+namespace ipl\Stdlib;
+
+use Evenement\EventEmitterTrait;
+use InvalidArgumentException;
+
+trait EventEmitter
+{
+    use EventEmitterTrait {
+        EventEmitterTrait::on as private evenementUnvalidatedOn;
+    }
+
+    /** @var array */
+    protected $eventsEmittedOnce = [];
+
+    /**
+     * @param string $event
+     * @param array $arguments
+     */
+    protected function emitOnce($event, array $arguments = [])
+    {
+        if (! isset($this->eventsEmittedOnce[$event])) {
+            $this->eventsEmittedOnce[$event] = true;
+            $this->emit($event, $arguments);
+        }
+    }
+
+    /**
+     * @param string $event
+     * @param callable $listener
+     * @return $this
+     */
+    public function on($event, callable $listener)
+    {
+        $this->assertValidEvent($event);
+        $this->evenementUnvalidatedOn($event, $listener);
+
+        return $this;
+    }
+
+    protected function assertValidEvent($event)
+    {
+        if (! $this->isValidEvent($event)) {
+            throw new InvalidArgumentException("$event is not a valid event");
+        }
+    }
+
+    /**
+     * @param string $event
+     * @return bool
+     */
+    public function isValidEvent($event)
+    {
+        return true;
+    }
+}