Support image url

A simpler implementation of
* #25

cc @DZunke

src/Message/ImageUrl.php

@@ -0,0 +1,33 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PhpLlm\LlmChain\Message;
+
+use Webmozart\Assert\Assert;
+
+final readonly class ImageUrl implements \JsonSerializable
+{
+    public function __construct(
+        public string $url,
+    ) {
+        Assert::stringNotEmpty($url);
+        Assert::startsWith($url, 'http');
+    }
+
+    /**
+     * @return array{
+     *     type: 'image_url',
+     *     image_url: array{url: non-empty-string}
+     * }
+     */
+    public function jsonSerialize(): array
+    {
+        return [
+            'type' => 'image_url',
+            'image_url' => [
+                'url' => $this->url,
+            ],
+        ];
+    }
+}

src/Message/Message.php

@@ -12,7 +12,7 @@
      * @param ?ToolCall[] $toolCalls
      */
     public function __construct(
-        public ?string $content,
+        public string|ImageUrl|null $content,
         public Role $role,
         public ?array $toolCalls = null,
     ) {
@@ -31,7 +31,7 @@ public static function ofAssistant(?string $content = null, ?array $toolCalls =
         return new self($content, Role::Assistant, $toolCalls);
     }
 
-    public static function ofUser(string $content): self
+    public static function ofUser(string|ImageUrl $content): self
     {
         return new self($content, Role::User);
     }
@@ -81,7 +81,14 @@ public function jsonSerialize(): array
         ];
 
         if (null !== $this->content) {
-            $array['content'] = $this->content;
+            $content = $this->content;
+
+            if ($this->content instanceof ImageUrl) {
+                $content = [];
+                $content[] = $this->content;
+            }
+
+            $array['content'] = $content;
         }
 
         if ($this->hasToolCalls() && $this->isToolCall()) {

tests/Message/MessageBagTest.php

@@ -4,6 +4,7 @@
 
 namespace PhpLlm\LlmChain\Tests\Message;
 
+use PhpLlm\LlmChain\Message\ImageUrl;
 use PhpLlm\LlmChain\Message\Message;
 use PhpLlm\LlmChain\Message\MessageBag;
 use PHPUnit\Framework\Attributes\CoversClass;
@@ -115,6 +116,8 @@ public function jsonSerialize(): void
             Message::forSystem('My amazing system prompt.'),
             Message::ofAssistant('It is time to sleep.'),
             Message::ofUser('Hello, world!'),
+            Message::ofUser('Analyze the following image:'),
+            Message::ofUser(new ImageUrl('http://example.com/image.jpg')),
         );
 
         $json = json_encode($messageBag);
@@ -125,6 +128,10 @@ public function jsonSerialize(): void
                 ['role' => 'system', 'content' => 'My amazing system prompt.'],
                 ['role' => 'assistant', 'content' => 'It is time to sleep.'],
                 ['role' => 'user', 'content' => 'Hello, world!'],
+                ['role' => 'user', 'content' => 'Analyze the following image:'],
+                ['role' => 'user', 'content' => [
+                    ['type' => 'image_url', 'image_url' => ['url' => 'http://example.com/image.jpg']],
+                ]],
             ]),
             $json
         );