refactor: migrate to DDD architecture with Dishka DI

Complete architectural refactoring from simple MVC to Clean Architecture/DDD pattern:

Domain Layer:

- Add entities (Post, BaseEntity) with business logic

- Add value objects (Title, Content, Slug) with validation

- Add repository interfaces (PostRepository)

- Add domain exceptions

Application Layer:

- Add use cases (CreatePost, GetPost, UpdatePost, DeletePost, ListPosts, PublishPost)

- Add DTOs for data transfer

- Add TransactionManager interface

Infrastructure Layer:

- Add SQLAlchemy models and async database connection

- Add SQLAlchemyPostRepository implementation

- Add Dishka DI container with providers

- Add error handlers and middleware

Presentation Layer:

- Add FastAPI routes with Dishka integration

- Add Pydantic schemas

- Add dependency injection using FromDishka[T]

Other Changes:

- Remove old flat structure (api/, common/, core/, modules/)

- Add hatchling build system for package scripts

- Add blog CLI command

- Update AGENTS.md with new architecture docs

- All 48 tests passing, mypy clean, ruff clean

tests/unit/domain/test_entities.py

@@ -0,0 +1,128 @@
+"""Tests for domain entities."""
+
+from uuid import UUID
+
+from app.domain.entities import Post
+from app.domain.value_objects import Content, Title
+
+
+class TestPost:
+    def test_post_creation(self) -> None:
+        """Test creating a post."""
+        post = Post.create(
+            title_str="Test Title",
+            content_str="This is test content that is long enough",
+            author_id="user-123",
+            tags=["test", "python"],
+        )
+
+        assert isinstance(post.id, UUID)
+        assert post.title.value == "Test Title"
+        assert post.content.value == "This is test content that is long enough"
+        assert post.slug.value == "test-title"
+        assert post.author_id == "user-123"
+        assert post.published is False
+        assert post.tags == ["test", "python"]
+
+    def test_post_publish(self) -> None:
+        """Test publishing a post."""
+        post = Post.create(
+            title_str="Test Title",
+            content_str="This is test content that is long enough",
+            author_id="user-123",
+        )
+
+        assert post.published is False
+        post.publish()
+        assert post.published is True
+
+    def test_post_unpublish(self) -> None:
+        """Test unpublishing a post."""
+        post = Post.create(
+            title_str="Test Title",
+            content_str="This is test content that is long enough",
+            author_id="user-123",
+        )
+
+        post.publish()
+        assert post.published is True
+        post.unpublish()
+        assert post.published is False
+
+    def test_post_update_title(self) -> None:
+        """Test updating post title."""
+        post = Post.create(
+            title_str="Original Title",
+            content_str="This is test content that is long enough",
+            author_id="user-123",
+        )
+
+        old_updated_at = post.updated_at
+        post.update_title(Title("New Title"))
+
+        assert post.title.value == "New Title"
+        assert post.slug.value == "new-title"
+        assert post.updated_at > old_updated_at
+
+    def test_post_update_content(self) -> None:
+        """Test updating post content."""
+        post = Post.create(
+            title_str="Test Title",
+            content_str="This is test content that is long enough",
+            author_id="user-123",
+        )
+
+        old_updated_at = post.updated_at
+        post.update_content(Content("Updated content that is also long enough"))
+
+        assert post.content.value == "Updated content that is also long enough"
+        assert post.updated_at > old_updated_at
+
+    def test_post_add_tag(self) -> None:
+        """Test adding a tag."""
+        post = Post.create(
+            title_str="Test Title",
+            content_str="This is test content that is long enough",
+            author_id="user-123",
+        )
+
+        post.add_tag("python")
+        assert "python" in post.tags
+
+        # Adding same tag twice should not duplicate
+        post.add_tag("python")
+        assert post.tags.count("python") == 1
+
+    def test_post_remove_tag(self) -> None:
+        """Test removing a tag."""
+        post = Post.create(
+            title_str="Test Title",
+            content_str="This is test content that is long enough",
+            author_id="user-123",
+            tags=["python", "fastapi"],
+        )
+
+        post.remove_tag("python")
+        assert "python" not in post.tags
+        assert "fastapi" in post.tags
+
+    def test_post_to_dict(self) -> None:
+        """Test converting post to dict."""
+        post = Post.create(
+            title_str="Test Title",
+            content_str="This is test content that is long enough",
+            author_id="user-123",
+            tags=["test"],
+        )
+
+        data = post.to_dict()
+
+        assert data["title"] == "Test Title"
+        assert data["content"] == "This is test content that is long enough"
+        assert data["slug"] == "test-title"
+        assert data["author_id"] == "user-123"
+        assert data["published"] is False
+        assert data["tags"] == ["test"]
+        assert "id" in data
+        assert "created_at" in data
+        assert "updated_at" in data

tests/unit/domain/test_exceptions.py

@@ -0,0 +1,48 @@
+"""Tests for domain exceptions."""
+
+from app.domain.exceptions import (
+    AlreadyExistsException,
+    DomainException,
+    ForbiddenException,
+    NotFoundException,
+    UnauthorizedException,
+    ValidationException,
+)
+
+
+class TestDomainExceptions:
+    def test_base_exception(self) -> None:
+        """Test base domain exception."""
+        exc = DomainException("Something went wrong")
+        assert exc.message == "Something went wrong"
+        assert str(exc) == "Something went wrong"
+
+    def test_validation_exception(self) -> None:
+        """Test validation exception."""
+        exc = ValidationException("Invalid input")
+        assert isinstance(exc, DomainException)
+        assert exc.message == "Invalid input"
+
+    def test_not_found_exception(self) -> None:
+        """Test not found exception."""
+        exc = NotFoundException("Resource not found")
+        assert isinstance(exc, DomainException)
+        assert exc.message == "Resource not found"
+
+    def test_already_exists_exception(self) -> None:
+        """Test already exists exception."""
+        exc = AlreadyExistsException("Already exists")
+        assert isinstance(exc, DomainException)
+        assert exc.message == "Already exists"
+
+    def test_unauthorized_exception(self) -> None:
+        """Test unauthorized exception."""
+        exc = UnauthorizedException("Unauthorized")
+        assert isinstance(exc, DomainException)
+        assert exc.message == "Unauthorized"
+
+    def test_forbidden_exception(self) -> None:
+        """Test forbidden exception."""
+        exc = ForbiddenException("Forbidden")
+        assert isinstance(exc, DomainException)
+        assert exc.message == "Forbidden"

tests/unit/domain/test_value_objects.py

@@ -0,0 +1,93 @@
+"""Tests for domain value objects."""
+
+import pytest
+
+from app.domain.value_objects import Content, Slug, Title
+
+
+class TestTitle:
+    def test_valid_title(self) -> None:
+        """Test creating a valid title."""
+        title = Title("Valid Title")
+        assert title.value == "Valid Title"
+
+    def test_title_too_short(self) -> None:
+        """Test title that is too short."""
+        with pytest.raises(ValueError, match="at least"):
+            Title("ab")
+
+    def test_title_too_long(self) -> None:
+        """Test title that is too long."""
+        with pytest.raises(ValueError, match="at most"):
+            Title("a" * 201)
+
+    def test_title_empty(self) -> None:
+        """Test empty title."""
+        with pytest.raises(ValueError, match="empty"):
+            Title("   ")
+
+    def test_title_not_string(self) -> None:
+        """Test non-string title."""
+        with pytest.raises(ValueError, match="string"):
+            Title(123)  # type: ignore[arg-type]
+
+
+class TestContent:
+    def test_valid_content(self) -> None:
+        """Test creating valid content."""
+        content = Content("This is valid content with enough characters")
+        assert content.value == "This is valid content with enough characters"
+
+    def test_content_too_short(self) -> None:
+        """Test content that is too short."""
+        with pytest.raises(ValueError, match="at least"):
+            Content("short")
+
+    def test_content_too_long(self) -> None:
+        """Test content that is too long."""
+        with pytest.raises(ValueError, match="at most"):
+            Content("a" * 50001)
+
+    def test_content_empty(self) -> None:
+        """Test empty content."""
+        with pytest.raises(ValueError, match="empty"):
+            Content("   ")
+
+
+class TestSlug:
+    def test_valid_slug(self) -> None:
+        """Test creating a valid slug."""
+        slug = Slug("valid-slug")
+        assert slug.value == "valid-slug"
+
+    def test_slug_from_title(self) -> None:
+        """Test generating slug from title."""
+        slug = Slug.from_title("Hello World Post")
+        assert slug.value == "hello-world-post"
+
+    def test_slug_from_title_with_special_chars(self) -> None:
+        """Test generating slug from title with special characters."""
+        slug = Slug.from_title("Hello, World! Post @#$%")
+        assert slug.value == "hello-world-post"
+
+    def test_slug_from_title_only_special_chars(self) -> None:
+        """Test generating slug from title with only special characters."""
+        slug = Slug.from_title("!@#$%")
+        assert slug.value == "post"
+
+    def test_slug_invalid_chars(self) -> None:
+        """Test slug with invalid characters."""
+        with pytest.raises(ValueError, match="lowercase"):
+            Slug("Invalid_Slug")
+
+    def test_slug_uppercase(self) -> None:
+        """Test slug with uppercase letters."""
+        with pytest.raises(ValueError, match="lowercase"):
+            Slug("Uppercase-Slug")
+
+    def test_slug_equality(self) -> None:
+        """Test slug value equality."""
+        slug1 = Slug("test-slug")
+        slug2 = Slug("test-slug")
+        assert slug1 == slug2
+        assert hash(slug1) == hash(slug2)