Clean up merging stuff

src copy/Core/Posts/EventPost.php

@@ -0,0 +1,27 @@
+<?php namespace Flarum\Core\Models;
+
+abstract class EventPost extends Post implements MergeableInterface
+{
+    use MergeableTrait;
+
+    /**
+     * Unserialize the content attribute.
+     *
+     * @param  string  $value
+     * @return string
+     */
+    public function getContentAttribute($value)
+    {
+        return json_decode($value, true);
+    }
+
+    /**
+     * Serialize the content attribute.
+     *
+     * @param  string  $value
+     */
+    public function setContentAttribute($value)
+    {
+        $this->attributes['content'] = json_encode($value);
+    }
+}

src copy/Core/Support/MergeableInterface.php

@@ -0,0 +1,6 @@
+<?php namespace Flarum\Core\Models;
+
+interface MergeableInterface
+{
+    public function saveAfter(Model $previous);
+}

src copy/Core/Support/MergeableTrait.php

@@ -0,0 +1,23 @@
+<?php namespace Flarum\Core\Models;
+
+trait MergeableTrait
+{
+    public function saveAfter(Model $previous)
+    {
+        if ($previous instanceof static) {
+            if ($merged = $this->mergeInto($previous)) {
+                $merged->save();
+                return $merged;
+            } else {
+                $previous->delete();
+                return $previous;
+            }
+        }
+
+        $this->save();
+
+        return $this;
+    }
+
+    abstract protected function mergeInto(Model $previous);
+}