Increase Short URL key entropy to decrease likelihood of key collisions

src/Classes/KeyGenerator.php

@@ -30,11 +30,24 @@ public function __construct(Hashids $hashids)
      */
     public function generateRandom(): string
     {
-        $ID = $this->getLastInsertedID();
+        $id = $this->getLastInsertedID();
+
+        $minKeyLength = $this->getKeyLength();
+
+        $currentLength = strlen((string) $id);
+
+        if ($currentLength > $minKeyLength) {
+            $minKeyLength = $currentLength;
+        }
 
         do {
-            $ID++;
-            $key = $this->hashids->encode($ID);
+            $id++;
+
+            $key = $this->hashids->encodeHex(
+                str_pad((string) $id, $minKeyLength - 1, uniqid())
+            );
+
+            $minKeyLength++;
         } while (ShortURL::where('url_key', $key)->exists());
 
         return $key;
@@ -52,6 +65,14 @@ public function generateKeyUsing(int $seed = null): string
             : $this->generateRandom();
     }
 
+    /**
+     * Get the minimum length of the Short URL key to generate.
+     */
+    protected function getKeyLength(): int
+    {
+        return config('short-url.key_length');
+    }
+
     /**
      * Get the ID of the last inserted ShortURL. This is done so that we can predict
      * what the ID of the ShortURL that will be inserted will be called. From doing

tests/Unit/Classes/BuilderTest.php

@@ -303,6 +303,18 @@ public function random_url_key_is_generated_if_one_is_not_explicitly_defined():
         $this->assertSame(5, strlen($shortURL->url_key));
     }
 
+    #[Test]
+    public function short_url_key_length_is_used(): void
+    {
+        Config::set('short-url.key_length', 3);
+
+        $builder = app(Builder::class);
+        $shortURL = $builder->destinationUrl('https://domain.com')->make();
+
+        $this->assertNotNull($shortURL->url_key);
+        $this->assertSame(3, strlen($shortURL->url_key));
+    }
+
     #[Test]
     public function short_url_can_be_created_and_stored_in_the_database(): void
     {

tests/Unit/Classes/KeyGeneratorTest.php

@@ -0,0 +1,42 @@
+<?php
+
+namespace AshAllenDesign\ShortURL\Tests\Unit\Classes;
+
+use AshAllenDesign\ShortURL\Classes\KeyGenerator;
+use AshAllenDesign\ShortURL\Models\ShortURL;
+use AshAllenDesign\ShortURL\Tests\Unit\TestCase;
+use PHPUnit\Framework\Attributes\Test;
+
+final class KeyGeneratorTest extends TestCase
+{
+    #[Test]
+    public function generates_expected_random_keys_based_on_last_inserted_id(): void
+    {
+        $generator = app(KeyGenerator::class);
+
+        $first = $generator->generateRandom();
+        $second = $generator->generateRandom();
+
+        ShortURL::factory()->create();
+
+        $third = $generator->generateRandom();
+
+        $this->assertEquals('NKYWm', $first);
+        $this->assertEquals('NKYWm', $second);
+        $this->assertEquals('N3LMR', $third);
+    }
+
+    #[Test]
+    public function generates_expected_key_using_seed(): void
+    {
+        $generator = app(KeyGenerator::class);
+
+        $first = $generator->generateKeyUsing(123);
+        $second = $generator->generateKeyUsing(123);
+        $third = $generator->generateKeyUsing(1234);
+
+        $this->assertEquals('4ZRw4', $first);
+        $this->assertEquals('4ZRw4', $second);
+        $this->assertEquals('4Ow94', $third);
+    }
+}