From 0d589340d9f9f841f3256682b859d2117daacb4d Mon Sep 17 00:00:00 2001
From: Yisroel Baum <yisroel.d.baum@gmail.com>
Date: Wed, 6 May 2026 22:13:37 +0300
Subject: [PATCH 1/8] add Comment entity, dto, repository interface

---
 backend/app/Comment/Comment.php           | 41 +++++++++++++++++++++++
 backend/app/Comment/CommentRepository.php | 17 ++++++++++
 backend/app/Comment/CreateCommentDto.php  | 15 +++++++++
 3 files changed, 73 insertions(+)
 create mode 100644 backend/app/Comment/Comment.php
 create mode 100644 backend/app/Comment/CommentRepository.php
 create mode 100644 backend/app/Comment/CreateCommentDto.php

diff --git a/backend/app/Comment/Comment.php b/backend/app/Comment/Comment.php
new file mode 100644
index 0000000..311b6c4
--- /dev/null
+++ b/backend/app/Comment/Comment.php
@@ -0,0 +1,41 @@
+<?php
+
+namespace App\Comment;
+
+use DateTimeImmutable;
+
+class Comment
+{
+    public function __construct(
+        private int $id,
+        private int $postId,
+        private int $userId,
+        private string $body,
+        private DateTimeImmutable $createdAt,
+    ) {}
+
+    public function getId(): int
+    {
+        return $this->id;
+    }
+
+    public function getPostId(): int
+    {
+        return $this->postId;
+    }
+
+    public function getUserId(): int
+    {
+        return $this->userId;
+    }
+
+    public function getBody(): string
+    {
+        return $this->body;
+    }
+
+    public function getCreatedAt(): DateTimeImmutable
+    {
+        return $this->createdAt;
+    }
+}
diff --git a/backend/app/Comment/CommentRepository.php b/backend/app/Comment/CommentRepository.php
new file mode 100644
index 0000000..7248d20
--- /dev/null
+++ b/backend/app/Comment/CommentRepository.php
@@ -0,0 +1,17 @@
+<?php
+
+namespace App\Comment;
+
+interface CommentRepository
+{
+    public function create(CreateCommentDto $dto): Comment;
+
+    public function find(int $id): ?Comment;
+
+    /**
+     * @return Comment[]
+     */
+    public function findByPostId(int $postId): array;
+
+    public function delete(int $id): void;
+}
diff --git a/backend/app/Comment/CreateCommentDto.php b/backend/app/Comment/CreateCommentDto.php
new file mode 100644
index 0000000..4513a0f
--- /dev/null
+++ b/backend/app/Comment/CreateCommentDto.php
@@ -0,0 +1,15 @@
+<?php
+
+namespace App\Comment;
+
+use DateTimeImmutable;
+
+readonly class CreateCommentDto
+{
+    public function __construct(
+        public int $postId,
+        public int $userId,
+        public string $body,
+        public DateTimeImmutable $createdAt,
+    ) {}
+}

From 93da08756cd3eeb7eef6575ffce8e31645b71a7d Mon Sep 17 00:00:00 2001
From: Yisroel Baum <yisroel.d.baum@gmail.com>
Date: Wed, 6 May 2026 22:14:11 +0300
Subject: [PATCH 2/8] add Comment persistence: model, migration, eloquent +
 fake repo

---
 backend/app/Comment/CommentModel.php          | 43 ++++++++++
 .../app/Comment/EloquentCommentRepository.php | 66 +++++++++++++++
 ...026_05_06_000004_create_comments_table.php | 28 +++++++
 backend/tests/Fakes/FakeCommentRepository.php | 82 +++++++++++++++++++
 4 files changed, 219 insertions(+)
 create mode 100644 backend/app/Comment/CommentModel.php
 create mode 100644 backend/app/Comment/EloquentCommentRepository.php
 create mode 100644 backend/database/migrations/2026_05_06_000004_create_comments_table.php
 create mode 100644 backend/tests/Fakes/FakeCommentRepository.php

diff --git a/backend/app/Comment/CommentModel.php b/backend/app/Comment/CommentModel.php
new file mode 100644
index 0000000..8182d94
--- /dev/null
+++ b/backend/app/Comment/CommentModel.php
@@ -0,0 +1,43 @@
+<?php
+
+namespace App\Comment;
+
+use DateTimeImmutable;
+use Illuminate\Database\Eloquent\Builder;
+use Illuminate\Database\Eloquent\Model;
+
+/**
+ * @property int $id
+ * @property int $post_id
+ * @property int $user_id
+ * @property string $body
+ * @property DateTimeImmutable $created_at
+ *
+ * @method static Builder<static>|CommentModel newModelQuery()
+ * @method static Builder<static>|CommentModel newQuery()
+ * @method static Builder<static>|CommentModel query()
+ * @method static Builder<static>|CommentModel whereId($value)
+ * @method static Builder<static>|CommentModel wherePostId($value)
+ * @method static Builder<static>|CommentModel whereUserId($value)
+ * @method static Builder<static>|CommentModel whereBody($value)
+ * @method static Builder<static>|CommentModel whereCreatedAt($value)
+ *
+ * @mixin \Eloquent
+ */
+class CommentModel extends Model
+{
+    protected $table = 'comments';
+
+    public $timestamps = false;
+
+    protected $fillable = [
+        'post_id',
+        'user_id',
+        'body',
+        'created_at',
+    ];
+
+    protected $casts = [
+        'created_at' => 'immutable_datetime',
+    ];
+}
diff --git a/backend/app/Comment/EloquentCommentRepository.php b/backend/app/Comment/EloquentCommentRepository.php
new file mode 100644
index 0000000..c2a3f5b
--- /dev/null
+++ b/backend/app/Comment/EloquentCommentRepository.php
@@ -0,0 +1,66 @@
+<?php
+
+namespace App\Comment;
+
+use DateTimeImmutable;
+use DateTimeZone;
+
+class EloquentCommentRepository implements CommentRepository
+{
+    public function create(CreateCommentDto $dto): Comment
+    {
+        $model = CommentModel::create([
+            'post_id' => $dto->postId,
+            'user_id' => $dto->userId,
+            'body' => $dto->body,
+            'created_at' => $dto->createdAt,
+        ]);
+
+        return $this->toDomain($model);
+    }
+
+    public function find(int $id): ?Comment
+    {
+        $model = CommentModel::find($id);
+
+        return $model === null ? null : $this->toDomain($model);
+    }
+
+    /**
+     * @return Comment[]
+     */
+    public function findByPostId(int $postId): array
+    {
+        $models = CommentModel::query()
+            ->where('post_id', $postId)
+            ->orderBy('created_at', 'asc')
+            ->get();
+
+        return $models->map(
+            function (CommentModel $model) {
+                return $this->toDomain($model);
+            },
+        )->all();
+    }
+
+    public function delete(int $id): void
+    {
+        CommentModel::query()->where('id', $id)->delete();
+    }
+
+    private function toDomain(CommentModel $model): Comment
+    {
+        $utc = new DateTimeZone('UTC');
+
+        return new Comment(
+            id: $model->id,
+            postId: $model->post_id,
+            userId: $model->user_id,
+            body: $model->body,
+            createdAt: new DateTimeImmutable(
+                $model->created_at->toDateTimeString(),
+                $utc,
+            ),
+        );
+    }
+}
diff --git a/backend/database/migrations/2026_05_06_000004_create_comments_table.php b/backend/database/migrations/2026_05_06_000004_create_comments_table.php
new file mode 100644
index 0000000..eea8665
--- /dev/null
+++ b/backend/database/migrations/2026_05_06_000004_create_comments_table.php
@@ -0,0 +1,28 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    public function up(): void
+    {
+        Schema::create('comments', function (Blueprint $table) {
+            $table->id();
+            $table->foreignId('post_id')
+                ->constrained('posts')
+                ->cascadeOnDelete();
+            $table->foreignId('user_id')
+                ->constrained('users')
+                ->cascadeOnDelete();
+            $table->text('body');
+            $table->dateTime('created_at')->index();
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::dropIfExists('comments');
+    }
+};
diff --git a/backend/tests/Fakes/FakeCommentRepository.php b/backend/tests/Fakes/FakeCommentRepository.php
new file mode 100644
index 0000000..7286f2d
--- /dev/null
+++ b/backend/tests/Fakes/FakeCommentRepository.php
@@ -0,0 +1,82 @@
+<?php
+
+namespace Tests\Fakes;
+
+use App\Comment\Comment;
+use App\Comment\CommentRepository;
+use App\Comment\CreateCommentDto;
+
+class FakeCommentRepository implements CommentRepository
+{
+    /**
+     * @var Comment[]
+     */
+    private array $existingComments = [];
+
+    public function create(CreateCommentDto $dto): Comment
+    {
+        $id = $this->getNextId();
+        $comment = new Comment(
+            id: $id,
+            postId: $dto->postId,
+            userId: $dto->userId,
+            body: $dto->body,
+            createdAt: $dto->createdAt,
+        );
+        $this->existingComments[$id] = $comment;
+
+        return $this->copy($comment);
+    }
+
+    public function find(int $id): ?Comment
+    {
+        $comment = $this->existingComments[$id] ?? null;
+        if ($comment === null) {
+            return null;
+        }
+
+        return $this->copy($comment);
+    }
+
+    /**
+     * @return Comment[]
+     */
+    public function findByPostId(int $postId): array
+    {
+        $matching = [];
+        foreach ($this->existingComments as $comment) {
+            if ($comment->getPostId() === $postId) {
+                $matching[] = $this->copy($comment);
+            }
+        }
+        usort(
+            $matching,
+            function (Comment $left, Comment $right) {
+                return $left->getCreatedAt() <=> $right->getCreatedAt();
+            },
+        );
+
+        return $matching;
+    }
+
+    public function delete(int $id): void
+    {
+        unset($this->existingComments[$id]);
+    }
+
+    private function copy(Comment $comment): Comment
+    {
+        return new Comment(
+            id: $comment->getId(),
+            postId: $comment->getPostId(),
+            userId: $comment->getUserId(),
+            body: $comment->getBody(),
+            createdAt: $comment->getCreatedAt(),
+        );
+    }
+
+    private function getNextId(): int
+    {
+        return count($this->existingComments) + 1;
+    }
+}

From 2557c9b6a901674480a4c6c74ae83777e8175cbc Mon Sep 17 00:00:00 2001
From: Yisroel Baum <yisroel.d.baum@gmail.com>
Date: Wed, 6 May 2026 22:14:31 +0300
Subject: [PATCH 3/8] test CreateComment use case

---
 .../Comment/UseCases/CreateCommentTest.php    | 138 ++++++++++++++++++
 1 file changed, 138 insertions(+)
 create mode 100644 backend/tests/Unit/Comment/UseCases/CreateCommentTest.php

diff --git a/backend/tests/Unit/Comment/UseCases/CreateCommentTest.php b/backend/tests/Unit/Comment/UseCases/CreateCommentTest.php
new file mode 100644
index 0000000..f35f8e8
--- /dev/null
+++ b/backend/tests/Unit/Comment/UseCases/CreateCommentTest.php
@@ -0,0 +1,138 @@
+<?php
+
+namespace Tests\Unit\Comment\UseCases;
+
+use App\Comment\UseCases\CreateComment\CreateComment;
+use App\Comment\UseCases\CreateComment\CreateCommentRequest;
+use App\Exceptions\BadRequestException;
+use App\Post\CreatePostDto;
+use DateTimeImmutable;
+use DateTimeZone;
+use DomainException;
+use Tests\Fakes\FakeClock;
+use Tests\Fakes\FakeCommentRepository;
+use Tests\Fakes\FakePostRepository;
+use Tests\TestCase;
+
+class CreateCommentTest extends TestCase
+{
+    private FakeCommentRepository $commentRepo;
+
+    private FakePostRepository $postRepo;
+
+    private FakeClock $clock;
+
+    private DateTimeImmutable $now;
+
+    private CreateComment $useCase;
+
+    protected function setUp(): void
+    {
+        $this->now = new DateTimeImmutable(
+            '2026-05-06T12:00:00',
+            new DateTimeZone('UTC'),
+        );
+        $this->commentRepo = new FakeCommentRepository;
+        $this->postRepo = new FakePostRepository;
+        $this->clock = new FakeClock($this->now);
+        $this->useCase = new CreateComment(
+            $this->commentRepo,
+            $this->postRepo,
+            $this->clock,
+        );
+    }
+
+    private function seedPost(): int
+    {
+        $post = $this->postRepo->create(new CreatePostDto(
+            userId: 1,
+            title: 'Some Post',
+            body: 'Body.',
+            createdAt: $this->now,
+        ));
+
+        return $post->getId();
+    }
+
+    public function test_zero_post_id_throws_bad_request(): void
+    {
+        $this->expectException(BadRequestException::class);
+        $this->useCase->execute(new CreateCommentRequest(
+            postId: 0,
+            userId: 1,
+            body: 'hi',
+        ));
+    }
+
+    public function test_zero_user_id_throws_bad_request(): void
+    {
+        $postId = $this->seedPost();
+        $this->expectException(BadRequestException::class);
+        $this->useCase->execute(new CreateCommentRequest(
+            postId: $postId,
+            userId: 0,
+            body: 'hi',
+        ));
+    }
+
+    public function test_null_body_throws_bad_request(): void
+    {
+        $postId = $this->seedPost();
+        $this->expectException(BadRequestException::class);
+        $this->useCase->execute(new CreateCommentRequest(
+            postId: $postId,
+            userId: 1,
+            body: null,
+        ));
+    }
+
+    public function test_blank_body_throws_bad_request(): void
+    {
+        $postId = $this->seedPost();
+        $this->expectException(BadRequestException::class);
+        $this->useCase->execute(new CreateCommentRequest(
+            postId: $postId,
+            userId: 1,
+            body: '   ',
+        ));
+    }
+
+    public function test_unknown_post_throws_domain_exception(): void
+    {
+        $this->expectException(DomainException::class);
+        $this->useCase->execute(new CreateCommentRequest(
+            postId: 999,
+            userId: 1,
+            body: 'hi',
+        ));
+    }
+
+    public function test_valid_create_returns_comment(): void
+    {
+        $postId = $this->seedPost();
+        $created = $this->useCase->execute(new CreateCommentRequest(
+            postId: $postId,
+            userId: 5,
+            body: '  Hello world  ',
+        ));
+
+        $this->assertSame($postId, $created->getPostId());
+        $this->assertSame(5, $created->getUserId());
+        $this->assertSame('Hello world', $created->getBody());
+        $this->assertEquals($this->now, $created->getCreatedAt());
+    }
+
+    public function test_created_comment_is_findable(): void
+    {
+        $postId = $this->seedPost();
+        $created = $this->useCase->execute(new CreateCommentRequest(
+            postId: $postId,
+            userId: 5,
+            body: 'Hello',
+        ));
+
+        $found = $this->commentRepo->find($created->getId());
+        $this->assertNotNull($found);
+        $this->assertSame('Hello', $found->getBody());
+    }
+}

From e8d2ff3fdfb02014c5e0576a06beab3fd380dcf4 Mon Sep 17 00:00:00 2001
From: Yisroel Baum <yisroel.d.baum@gmail.com>
Date: Wed, 6 May 2026 22:14:55 +0300
Subject: [PATCH 4/8] implement CreateComment use case

---
 .../UseCases/CreateComment/CreateComment.php  | 49 +++++++++++++++++++
 .../CreateComment/CreateCommentRequest.php    | 12 +++++
 2 files changed, 61 insertions(+)
 create mode 100644 backend/app/Comment/UseCases/CreateComment/CreateComment.php
 create mode 100644 backend/app/Comment/UseCases/CreateComment/CreateCommentRequest.php

diff --git a/backend/app/Comment/UseCases/CreateComment/CreateComment.php b/backend/app/Comment/UseCases/CreateComment/CreateComment.php
new file mode 100644
index 0000000..1987b5d
--- /dev/null
+++ b/backend/app/Comment/UseCases/CreateComment/CreateComment.php
@@ -0,0 +1,49 @@
+<?php
+
+namespace App\Comment\UseCases\CreateComment;
+
+use App\Auth\Clock;
+use App\Comment\Comment;
+use App\Comment\CommentRepository;
+use App\Comment\CreateCommentDto;
+use App\Exceptions\BadRequestException;
+use App\Post\PostRepository;
+use DomainException;
+
+class CreateComment
+{
+    public function __construct(
+        private CommentRepository $commentRepo,
+        private PostRepository $postRepo,
+        private Clock $clock,
+    ) {}
+
+    /**
+     * @throws BadRequestException
+     * @throws DomainException
+     */
+    public function execute(CreateCommentRequest $request): Comment
+    {
+        if ($request->postId <= 0) {
+            throw new BadRequestException('postId must be positive');
+        }
+        if ($request->userId <= 0) {
+            throw new BadRequestException('userId must be positive');
+        }
+        $body = $request->body === null ? '' : trim($request->body);
+        if ($body === '') {
+            throw new BadRequestException('body is required');
+        }
+
+        if ($this->postRepo->find($request->postId) === null) {
+            throw new DomainException('post not found');
+        }
+
+        return $this->commentRepo->create(new CreateCommentDto(
+            postId: $request->postId,
+            userId: $request->userId,
+            body: $body,
+            createdAt: $this->clock->now(),
+        ));
+    }
+}
diff --git a/backend/app/Comment/UseCases/CreateComment/CreateCommentRequest.php b/backend/app/Comment/UseCases/CreateComment/CreateCommentRequest.php
new file mode 100644
index 0000000..d2984bb
--- /dev/null
+++ b/backend/app/Comment/UseCases/CreateComment/CreateCommentRequest.php
@@ -0,0 +1,12 @@
+<?php
+
+namespace App\Comment\UseCases\CreateComment;
+
+class CreateCommentRequest
+{
+    public function __construct(
+        public int $postId,
+        public int $userId,
+        public ?string $body,
+    ) {}
+}

From f9e2529994176cce3c107d5d581a89a3194c8dd2 Mon Sep 17 00:00:00 2001
From: Yisroel Baum <yisroel.d.baum@gmail.com>
Date: Wed, 6 May 2026 22:15:10 +0300
Subject: [PATCH 5/8] test ListCommentsForPost use case

---
 .../UseCases/ListCommentsForPostTest.php      | 73 +++++++++++++++++++
 1 file changed, 73 insertions(+)
 create mode 100644 backend/tests/Unit/Comment/UseCases/ListCommentsForPostTest.php

diff --git a/backend/tests/Unit/Comment/UseCases/ListCommentsForPostTest.php b/backend/tests/Unit/Comment/UseCases/ListCommentsForPostTest.php
new file mode 100644
index 0000000..b69a25e
--- /dev/null
+++ b/backend/tests/Unit/Comment/UseCases/ListCommentsForPostTest.php
@@ -0,0 +1,73 @@
+<?php
+
+namespace Tests\Unit\Comment\UseCases;
+
+use App\Comment\CreateCommentDto;
+use App\Comment\UseCases\ListCommentsForPost\ListCommentsForPost;
+use App\Comment\UseCases\ListCommentsForPost\ListCommentsForPostRequest;
+use App\Exceptions\BadRequestException;
+use DateTimeImmutable;
+use DateTimeZone;
+use Tests\Fakes\FakeCommentRepository;
+use Tests\TestCase;
+
+class ListCommentsForPostTest extends TestCase
+{
+    private FakeCommentRepository $commentRepo;
+
+    private ListCommentsForPost $useCase;
+
+    private DateTimeImmutable $now;
+
+    protected function setUp(): void
+    {
+        $this->now = new DateTimeImmutable(
+            '2026-05-06T12:00:00',
+            new DateTimeZone('UTC'),
+        );
+        $this->commentRepo = new FakeCommentRepository;
+        $this->useCase = new ListCommentsForPost($this->commentRepo);
+    }
+
+    private function seed(int $postId, string $body, string $offset): void
+    {
+        $this->commentRepo->create(new CreateCommentDto(
+            postId: $postId,
+            userId: 1,
+            body: $body,
+            createdAt: $this->now->modify($offset),
+        ));
+    }
+
+    public function test_zero_post_id_throws_bad_request(): void
+    {
+        $this->expectException(BadRequestException::class);
+        $this->useCase->execute(new ListCommentsForPostRequest(
+            postId: 0,
+        ));
+    }
+
+    public function test_returns_empty_list_when_no_comments(): void
+    {
+        $result = $this->useCase->execute(new ListCommentsForPostRequest(
+            postId: 1,
+        ));
+
+        $this->assertSame([], $result);
+    }
+
+    public function test_returns_only_comments_for_given_post(): void
+    {
+        $this->seed(1, 'first', '+0 seconds');
+        $this->seed(2, 'other-post', '+0 seconds');
+        $this->seed(1, 'second', '+1 minute');
+
+        $result = $this->useCase->execute(new ListCommentsForPostRequest(
+            postId: 1,
+        ));
+
+        $this->assertCount(2, $result);
+        $this->assertSame('first', $result[0]->getBody());
+        $this->assertSame('second', $result[1]->getBody());
+    }
+}

From a59fc4890ffc467a5ae840e605eed5c1841c324a Mon Sep 17 00:00:00 2001
From: Yisroel Baum <yisroel.d.baum@gmail.com>
Date: Wed, 6 May 2026 22:15:49 +0300
Subject: [PATCH 6/8] implement ListCommentsForPost use case

Renames seed() helper to seedComment() to avoid clashing with
Illuminate\Foundation\Testing\TestCase::seed().
---
 .../ListCommentsForPost.php                   | 28 +++++++++++++++++++
 .../ListCommentsForPostRequest.php            | 10 +++++++
 .../UseCases/ListCommentsForPostTest.php      |  8 +++---
 3 files changed, 42 insertions(+), 4 deletions(-)
 create mode 100644 backend/app/Comment/UseCases/ListCommentsForPost/ListCommentsForPost.php
 create mode 100644 backend/app/Comment/UseCases/ListCommentsForPost/ListCommentsForPostRequest.php

diff --git a/backend/app/Comment/UseCases/ListCommentsForPost/ListCommentsForPost.php b/backend/app/Comment/UseCases/ListCommentsForPost/ListCommentsForPost.php
new file mode 100644
index 0000000..13cf6c4
--- /dev/null
+++ b/backend/app/Comment/UseCases/ListCommentsForPost/ListCommentsForPost.php
@@ -0,0 +1,28 @@
+<?php
+
+namespace App\Comment\UseCases\ListCommentsForPost;
+
+use App\Comment\Comment;
+use App\Comment\CommentRepository;
+use App\Exceptions\BadRequestException;
+
+class ListCommentsForPost
+{
+    public function __construct(
+        private CommentRepository $commentRepo,
+    ) {}
+
+    /**
+     * @return Comment[]
+     *
+     * @throws BadRequestException
+     */
+    public function execute(ListCommentsForPostRequest $request): array
+    {
+        if ($request->postId <= 0) {
+            throw new BadRequestException('postId must be positive');
+        }
+
+        return $this->commentRepo->findByPostId($request->postId);
+    }
+}
diff --git a/backend/app/Comment/UseCases/ListCommentsForPost/ListCommentsForPostRequest.php b/backend/app/Comment/UseCases/ListCommentsForPost/ListCommentsForPostRequest.php
new file mode 100644
index 0000000..6f53289
--- /dev/null
+++ b/backend/app/Comment/UseCases/ListCommentsForPost/ListCommentsForPostRequest.php
@@ -0,0 +1,10 @@
+<?php
+
+namespace App\Comment\UseCases\ListCommentsForPost;
+
+class ListCommentsForPostRequest
+{
+    public function __construct(
+        public int $postId,
+    ) {}
+}
diff --git a/backend/tests/Unit/Comment/UseCases/ListCommentsForPostTest.php b/backend/tests/Unit/Comment/UseCases/ListCommentsForPostTest.php
index b69a25e..7ed8918 100644
--- a/backend/tests/Unit/Comment/UseCases/ListCommentsForPostTest.php
+++ b/backend/tests/Unit/Comment/UseCases/ListCommentsForPostTest.php
@@ -29,7 +29,7 @@ class ListCommentsForPostTest extends TestCase
         $this->useCase = new ListCommentsForPost($this->commentRepo);
     }
 
-    private function seed(int $postId, string $body, string $offset): void
+    private function seedComment(int $postId, string $body, string $offset): void
     {
         $this->commentRepo->create(new CreateCommentDto(
             postId: $postId,
@@ -58,9 +58,9 @@ class ListCommentsForPostTest extends TestCase
 
     public function test_returns_only_comments_for_given_post(): void
     {
-        $this->seed(1, 'first', '+0 seconds');
-        $this->seed(2, 'other-post', '+0 seconds');
-        $this->seed(1, 'second', '+1 minute');
+        $this->seedComment(1, 'first', '+0 seconds');
+        $this->seedComment(2, 'other-post', '+0 seconds');
+        $this->seedComment(1, 'second', '+1 minute');
 
         $result = $this->useCase->execute(new ListCommentsForPostRequest(
             postId: 1,

From 5bbef871dbfb391f6cc493dd91d6ad051c573a8c Mon Sep 17 00:00:00 2001
From: Yisroel Baum <yisroel.d.baum@gmail.com>
Date: Wed, 6 May 2026 22:16:10 +0300
Subject: [PATCH 7/8] test DeleteComment use case

---
 .../Comment/UseCases/DeleteCommentTest.php    | 131 ++++++++++++++++++
 1 file changed, 131 insertions(+)
 create mode 100644 backend/tests/Unit/Comment/UseCases/DeleteCommentTest.php

diff --git a/backend/tests/Unit/Comment/UseCases/DeleteCommentTest.php b/backend/tests/Unit/Comment/UseCases/DeleteCommentTest.php
new file mode 100644
index 0000000..c3752a7
--- /dev/null
+++ b/backend/tests/Unit/Comment/UseCases/DeleteCommentTest.php
@@ -0,0 +1,131 @@
+<?php
+
+namespace Tests\Unit\Comment\UseCases;
+
+use App\Comment\Comment;
+use App\Comment\CreateCommentDto;
+use App\Comment\UseCases\DeleteComment\DeleteComment;
+use App\Comment\UseCases\DeleteComment\DeleteCommentRequest;
+use App\Exceptions\BadRequestException;
+use App\Exceptions\ForbiddenException;
+use DateTimeImmutable;
+use DateTimeZone;
+use Tests\Fakes\FakeCommentRepository;
+use Tests\TestCase;
+
+class DeleteCommentTest extends TestCase
+{
+    private FakeCommentRepository $commentRepo;
+
+    private DateTimeImmutable $now;
+
+    private DeleteComment $useCase;
+
+    protected function setUp(): void
+    {
+        $this->now = new DateTimeImmutable(
+            '2026-05-06T12:00:00',
+            new DateTimeZone('UTC'),
+        );
+        $this->commentRepo = new FakeCommentRepository;
+        $this->useCase = new DeleteComment($this->commentRepo);
+    }
+
+    private function seedCommentByUser(int $userId): Comment
+    {
+        return $this->commentRepo->create(new CreateCommentDto(
+            postId: 1,
+            userId: $userId,
+            body: 'comment body',
+            createdAt: $this->now,
+        ));
+    }
+
+    public function test_zero_comment_id_throws_bad_request(): void
+    {
+        $this->expectException(BadRequestException::class);
+        $this->useCase->execute(new DeleteCommentRequest(
+            commentId: 0,
+            requesterId: 1,
+            requesterIsAdmin: false,
+        ));
+    }
+
+    public function test_zero_requester_id_throws_bad_request(): void
+    {
+        $comment = $this->seedCommentByUser(1);
+
+        $this->expectException(BadRequestException::class);
+        $this->useCase->execute(new DeleteCommentRequest(
+            commentId: $comment->getId(),
+            requesterId: 0,
+            requesterIsAdmin: false,
+        ));
+    }
+
+    public function test_unknown_comment_is_no_op(): void
+    {
+        $this->useCase->execute(new DeleteCommentRequest(
+            commentId: 999,
+            requesterId: 1,
+            requesterIsAdmin: false,
+        ));
+
+        $this->assertNull($this->commentRepo->find(999));
+    }
+
+    public function test_author_can_delete_own_comment(): void
+    {
+        $comment = $this->seedCommentByUser(1);
+
+        $this->useCase->execute(new DeleteCommentRequest(
+            commentId: $comment->getId(),
+            requesterId: 1,
+            requesterIsAdmin: false,
+        ));
+
+        $this->assertNull($this->commentRepo->find($comment->getId()));
+    }
+
+    public function test_admin_can_delete_anyones_comment(): void
+    {
+        $comment = $this->seedCommentByUser(1);
+
+        $this->useCase->execute(new DeleteCommentRequest(
+            commentId: $comment->getId(),
+            requesterId: 99,
+            requesterIsAdmin: true,
+        ));
+
+        $this->assertNull($this->commentRepo->find($comment->getId()));
+    }
+
+    public function test_other_user_cannot_delete_comment(): void
+    {
+        $comment = $this->seedCommentByUser(1);
+
+        $this->expectException(ForbiddenException::class);
+        $this->useCase->execute(new DeleteCommentRequest(
+            commentId: $comment->getId(),
+            requesterId: 2,
+            requesterIsAdmin: false,
+        ));
+    }
+
+    public function test_forbidden_delete_does_not_remove_comment(): void
+    {
+        $comment = $this->seedCommentByUser(1);
+
+        try {
+            $this->useCase->execute(new DeleteCommentRequest(
+                commentId: $comment->getId(),
+                requesterId: 2,
+                requesterIsAdmin: false,
+            ));
+        } catch (ForbiddenException) {
+            // expected
+        }
+
+        $this->assertNotNull($this->commentRepo->find($comment->getId()));
+    }
+}

From d24bde3761a9d45a58b70e65f1ecc3752b69f111 Mon Sep 17 00:00:00 2001
From: Yisroel Baum <yisroel.d.baum@gmail.com>
Date: Wed, 6 May 2026 22:16:34 +0300
Subject: [PATCH 8/8] implement DeleteComment use case

---
 .../UseCases/DeleteComment/DeleteComment.php  | 42 +++++++++++++++++++
 .../DeleteComment/DeleteCommentRequest.php    | 12 ++++++
 2 files changed, 54 insertions(+)
 create mode 100644 backend/app/Comment/UseCases/DeleteComment/DeleteComment.php
 create mode 100644 backend/app/Comment/UseCases/DeleteComment/DeleteCommentRequest.php

diff --git a/backend/app/Comment/UseCases/DeleteComment/DeleteComment.php b/backend/app/Comment/UseCases/DeleteComment/DeleteComment.php
new file mode 100644
index 0000000..daa8798
--- /dev/null
+++ b/backend/app/Comment/UseCases/DeleteComment/DeleteComment.php
@@ -0,0 +1,42 @@
+<?php
+
+namespace App\Comment\UseCases\DeleteComment;
+
+use App\Comment\CommentRepository;
+use App\Exceptions\BadRequestException;
+use App\Exceptions\ForbiddenException;
+
+class DeleteComment
+{
+    public function __construct(
+        private CommentRepository $commentRepo,
+    ) {}
+
+    /**
+     * @throws BadRequestException
+     * @throws ForbiddenException
+     */
+    public function execute(DeleteCommentRequest $request): void
+    {
+        if ($request->commentId <= 0) {
+            throw new BadRequestException('commentId must be positive');
+        }
+        if ($request->requesterId <= 0) {
+            throw new BadRequestException('requesterId must be positive');
+        }
+
+        $comment = $this->commentRepo->find($request->commentId);
+        if ($comment === null) {
+            return;
+        }
+
+        $isAuthor = $comment->getUserId() === $request->requesterId;
+        if (! $isAuthor && ! $request->requesterIsAdmin) {
+            throw new ForbiddenException(
+                'requester is not allowed to delete this comment'
+            );
+        }
+
+        $this->commentRepo->delete($request->commentId);
+    }
+}
diff --git a/backend/app/Comment/UseCases/DeleteComment/DeleteCommentRequest.php b/backend/app/Comment/UseCases/DeleteComment/DeleteCommentRequest.php
new file mode 100644
index 0000000..9dfaa2e
--- /dev/null
+++ b/backend/app/Comment/UseCases/DeleteComment/DeleteCommentRequest.php
@@ -0,0 +1,12 @@
+<?php
+
+namespace App\Comment\UseCases\DeleteComment;
+
+class DeleteCommentRequest
+{
+    public function __construct(
+        public int $commentId,
+        public int $requesterId,
+        public bool $requesterIsAdmin,
+    ) {}
+}