Match tag names case-insensitively

app/Models/Tag.php

@@ -58,6 +58,30 @@ public static function nameHasChanged($tagId, string $newName): bool
         return $oldName !== $newName;
     }
 
+    /**
+     * Override inherited function such that it finds existing tags case-insensitively, but creates them with the right casing
+     *
+     * @param array $attributes
+     * @param array $values
+     * @return Builder
+     */
+    public static function firstOrCreate(array $attributes = [], array $values = []): self
+    {
+        if (isset($attributes['name'])) {
+            // SQL lower() function is checked to be supported by MariaDB, SQLite, PostgreSQL, and MSSQL
+            $existing = self::whereRaw('lower(name) = lower(?)', [$attributes['name']])->first();
+            if (!is_null($existing)) {
+                return $existing;
+            }
+        }
+
+        if (!is_null($instance = self::where($attributes)->first())) {
+            return $instance;
+        }
+
+        return self::createOrFirst($attributes, $values);
+    }
+
     /*
      | ========================================================================
      | SCOPES

tests/Models/LinkCreateTest.php

@@ -65,4 +65,41 @@ public function testValidLinkCreation(): void
 
         $this->assertDatabaseHas('links', $assertedData);
     }
+
+    public function testCaseInsensitiveTagAssignation(): void
+    {
+        $this->be($this->user);
+
+        $tag = 'CERN';
+        $tagVariant = ucfirst(strtolower($tag));
+
+        $this->assertNotEquals($tag, $tagVariant);
+
+        $link1Data = [
+            'title' => 'Link1Name',
+            'url' => 'https://cern.int/science/physics/antimatter',
+            'tags' => $tag,
+        ];
+        $link2Data = [
+            'title' => 'Link2Name',
+            'url' => 'https://cern.int/science/accelerators/large-hadron-collider/safety-lhc',
+            'tags' => $tagVariant,
+        ];
+
+        $link1 = LinkRepository::create($link1Data);
+        $link2 = LinkRepository::create($link2Data);
+
+        // Ensure that the casing in $tag is preserved
+        $this->assertEquals($link1->tags->first()->name, $tag);
+
+        // Ensure that $tag was identified as a duplicate of $tagVariant and used instead of the variant
+        $this->assertEquals($link2->tags->first()->name, $tag);
+        $this->assertEquals($link1->tags->first()->id, $link2->tags->first()->id);
+
+        // Ensure that only the correct variant exists
+        $negativeTagData = [
+            'name' => $tagVariant,
+        ];
+        $this->assertDatabaseMissing('tags', $negativeTagData);
+    }
 }