use model observer to manage tagging of notes

app/Observers/NoteObserver.php

@@ -0,0 +1,76 @@
+<?php
+
+namespace App\Observers;
+
+use App\{Note, Tag};
+
+class NoteObserver
+{
+    /**
+     * Listen to the Note created event.
+     *
+     * @param  \App\Note  $note
+     * @return void
+     */
+    public function created(Note $note)
+    {
+        $tags = $this->getTagsFromNote($note->getAttributes()['note']);
+
+        if (count($tags) === 0) {
+            return;
+        }
+
+        $tags->transform(function ($tag) {
+            return Tag::firstOrCreate(['tag' => $tag]);
+        });
+
+        $note->tags()->attach($tags->map(function ($tag) {
+            return $tag->id;
+        }));
+    }
+
+    /**
+     * Listen to the Note updated event.
+     *
+     * @param  \App\Note  $Note
+     * @return void
+     */
+    public function updated(Note $note)
+    {
+        $tags = $this->getTagsFromNote($note->getAttributes()['note']);
+        if (count($tags) === 0) {
+            return;
+        }
+
+        $tags->transform(function ($tag) {
+            return Tag::firstOrCreate(['tag' => $tag]);
+        });
+
+        $note->tags()->sync($tags->map(function ($tag) {
+            return $tag->id;
+        }));
+    }
+
+    /**
+     * Listen to the Note deleting event.
+     *
+     * @param  \App\Note  $note
+     * @return void
+     */
+    public function deleting(Note $note)
+    {
+        $note->tags()->detach();
+    }
+
+    public function getTagsFromNote($note)
+    {
+        preg_match_all('/#([^\s<>]+)\b/', $note, $tags);
+        if (array_get($tags, '1') === null) {
+            return [];
+        }
+
+        return collect($tags[1])->map(function ($tag) {
+            return Tag::normalize($tag);
+        })->unique();
+    }
+}