feat: add FastAPI, Entity base class, and health check endpoint

.agent/current-plan.md

@@ -1,27 +1,18 @@
-# Plan: UserId Value Object
+# Plan: Add FastAPI to the Project
 
-## Status: COMPLETED
+## Goal
+Add FastAPI as the web framework with a minimal health check endpoint.
 
-## Objective
-Create a UserId value object in the marketplace domain with an immutable UUID value.
+## Changes
 
-## Decisions Made
-- **Location**: `domain/marketplace/user_id.py`
-- **Class style**: `@dataclass(frozen=True)` for immutability
-- **Tests**: Yes
+### 1. Dependencies
+- Add `fastapi` and `uvicorn[standard]` to `pyproject.toml` under `[project.dependencies]`
+- Install dependencies into the virtual environment
 
-## Value Object Structure
-```python
-@dataclass(frozen=True)
-class UserId:
-    value: UUID
-```
+### 2. Application Entry Point
+- Create `main.py` with a FastAPI app instance
+- Add a health check endpoint (`GET /`) that returns `{"status": "ok"}`
 
-## Files Created
-- `domain/marketplace/user_id.py`
-- `tests/test_user_id.py`
-
-## Test Results
-- `test_user_id_creation` - PASSED
-- `test_user_id_is_immutable` - PASSED
-- `test_user_id_equality` - PASSED
+## Verification
+- `pytest tests/` — all tests pass
+- `uvicorn main:app --reload` — server starts and health endpoint responds

.gitignore

@@ -1,4 +1,4 @@
-env/
+.venv/
 __pycache__/
 *.pyc
 .pytest_cache/

domain/framework/entity.py

@@ -0,0 +1,18 @@
+from abc import ABC
+from dataclasses import replace
+from typing import Self
+
+from domain.marketplace.domain_event import DomainEvent
+
+
+class Entity(ABC):
+    _events: tuple[DomainEvent, ...] = ()
+
+    def raise_event(self, event: DomainEvent) -> Self:
+        return replace(self, _events=(*self._events, event))
+
+    def get_changes(self) -> tuple[DomainEvent, ...]:
+        return self._events
+
+    def clear_changes(self) -> Self:
+        return replace(self, _events=())

main.py

@@ -0,0 +1,8 @@
+from fastapi import FastAPI
+
+app = FastAPI()
+
+
+@app.get("/")
+def health_check():
+    return {"status": "ok"}

pyproject.toml

@@ -6,6 +6,10 @@ build-backend = "setuptools.backends._legacy:_Backend"
 name = "python-fun"
 version = "0.1.0"
 requires-python = ">=3.12"
+dependencies = [
+    "fastapi>=0.115.0",
+    "uvicorn[standard]>=0.30.0",
+]
 
 [tool.pytest.ini_options]
 pythonpath = ["."]

tests/test_entity.py

@@ -0,0 +1,79 @@
+from dataclasses import dataclass
+from uuid import uuid4
+
+from domain.framework.entity import Entity
+from domain.marketplace.domain_event import (
+    ClassifiedAdCreated,
+    ClassifiedAdSentForReview,
+    DomainEvent,
+)
+
+
+@dataclass(frozen=True)
+class TestEntity(Entity):
+    __test__ = False
+    _events: tuple[DomainEvent, ...] = ()
+
+
+def test_entity_creation():
+    entity = TestEntity()
+    assert entity.get_changes() == ()
+
+
+def test_raise_event_returns_new_instance_with_event():
+    entity = TestEntity()
+    event = ClassifiedAdCreated(id=uuid4(), owner_id=uuid4())
+
+    new_entity = entity.raise_event(event)
+
+    assert new_entity.get_changes() == (event,)
+
+
+def test_raise_event_does_not_mutate_original():
+    entity = TestEntity()
+    event = ClassifiedAdCreated(id=uuid4(), owner_id=uuid4())
+
+    entity.raise_event(event)
+
+    assert entity.get_changes() == ()
+
+
+def test_multiple_events_accumulate():
+    entity = TestEntity()
+    event1 = ClassifiedAdCreated(id=uuid4(), owner_id=uuid4())
+    event2 = ClassifiedAdSentForReview(id=uuid4())
+
+    entity = entity.raise_event(event1)
+    entity = entity.raise_event(event2)
+
+    assert entity.get_changes() == (event1, event2)
+
+
+def test_clear_changes_returns_instance_with_empty_events():
+    entity = TestEntity()
+    event = ClassifiedAdCreated(id=uuid4(), owner_id=uuid4())
+    entity = entity.raise_event(event)
+
+    cleared = entity.clear_changes()
+
+    assert cleared.get_changes() == ()
+
+
+def test_clear_changes_does_not_mutate_original():
+    entity = TestEntity()
+    event = ClassifiedAdCreated(id=uuid4(), owner_id=uuid4())
+    entity = entity.raise_event(event)
+
+    entity.clear_changes()
+
+    assert entity.get_changes() == (event,)
+
+
+def test_get_changes_returns_tuple():
+    entity = TestEntity()
+    event = ClassifiedAdCreated(id=uuid4(), owner_id=uuid4())
+    entity = entity.raise_event(event)
+
+    changes = entity.get_changes()
+
+    assert isinstance(changes, tuple)