feat: add runnable simulator foundation

app/__init__.py

@@ -0,0 +1 @@
+"""Proxmox API simulator application package."""

app/api/__init__.py

@@ -0,0 +1 @@
+"""HTTP adapters."""

app/api/errors.py

@@ -0,0 +1,25 @@
+"""Base external error representation."""
+
+from __future__ import annotations
+
+import logging
+from typing import Any
+
+from fastapi import Request
+from fastapi.responses import JSONResponse
+
+logger = logging.getLogger(__name__)
+
+
+async def unhandled_exception_handler(request: Request, exc: Exception) -> JSONResponse:
+    """Log internal failures and return a stable non-FastAPI error envelope."""
+
+    logger.exception(
+        "unhandled request error",
+        extra={"request_id": getattr(request.state, "request_id", None), "path": request.url.path},
+    )
+    body: dict[str, Any] = {
+        "data": None,
+        "errors": {"internal": "internal server error"},
+    }
+    return JSONResponse(status_code=500, content=body)

app/api/middleware.py

@@ -0,0 +1,42 @@
+"""Request correlation and access logging middleware."""
+
+from __future__ import annotations
+
+import logging
+import time
+import uuid
+from collections.abc import Awaitable, Callable
+
+from fastapi import Request, Response
+from starlette.middleware.base import BaseHTTPMiddleware
+
+logger = logging.getLogger(__name__)
+
+RequestHandler = Callable[[Request], Awaitable[Response]]
+
+
+class RequestContextMiddleware(BaseHTTPMiddleware):
+    """Attach a bounded request ID and log one structured completion event."""
+
+    def __init__(self, app: object, header_name: str) -> None:
+        super().__init__(app)  # type: ignore[arg-type]
+        self._header_name = header_name
+
+    async def dispatch(self, request: Request, call_next: RequestHandler) -> Response:
+        supplied = request.headers.get(self._header_name, "")
+        request_id = supplied if 0 < len(supplied) <= 128 else str(uuid.uuid4())
+        request.state.request_id = request_id
+        started = time.monotonic()
+        response = await call_next(request)
+        response.headers[self._header_name] = request_id
+        logger.info(
+            "request completed",
+            extra={
+                "request_id": request_id,
+                "method": request.method,
+                "path": request.url.path,
+                "status": response.status_code,
+                "duration_ms": round((time.monotonic() - started) * 1000, 3),
+            },
+        )
+        return response

app/config.py

@@ -0,0 +1,39 @@
+"""Typed application configuration."""
+
+from __future__ import annotations
+
+from functools import lru_cache
+
+from pydantic import Field, SecretStr
+from pydantic_settings import BaseSettings, SettingsConfigDict
+
+
+class Settings(BaseSettings):
+    """Runtime settings loaded from environment variables and an optional `.env`."""
+
+    model_config = SettingsConfigDict(
+        env_file=".env",
+        env_file_encoding="utf-8",
+        extra="ignore",
+        frozen=True,
+    )
+
+    app_name: str = "proxmox-api-simulator"
+    app_host: str = "0.0.0.0"  # noqa: S104 - the container must accept external traffic
+    app_port: int = Field(default=8006, ge=1, le=65535)
+    database_url: SecretStr = SecretStr(
+        "postgresql://proxmox:proxmox@localhost:5432/proxmox_simulator"
+    )
+    db_pool_min_size: int = Field(default=1, ge=1, le=100)
+    db_pool_max_size: int = Field(default=10, ge=1, le=100)
+    db_connect_timeout_seconds: float = Field(default=10.0, gt=0, le=60)
+    db_command_timeout_seconds: float = Field(default=30.0, gt=0, le=300)
+    log_level: str = "INFO"
+    request_id_header: str = "X-Request-ID"
+
+
+@lru_cache(maxsize=1)
+def get_settings() -> Settings:
+    """Return the immutable process configuration."""
+
+    return Settings()

app/db/__init__.py

@@ -0,0 +1 @@
+"""PostgreSQL infrastructure."""

app/db/pool.py

@@ -0,0 +1,79 @@
+"""Small typed asyncpg pool boundary."""
+
+from __future__ import annotations
+
+from typing import Protocol, Self, cast
+
+import asyncpg  # type: ignore[import-untyped]
+from asyncpg import Pool
+
+from app.config import Settings
+
+
+class Database(Protocol):
+    """Application-facing database lifecycle and health interface."""
+
+    async def connect(self) -> None: ...
+
+    async def close(self) -> None: ...
+
+    async def is_ready(self) -> bool: ...
+
+
+class AsyncpgDatabase:
+    """Own an asyncpg pool without exposing it as global mutable state."""
+
+    def __init__(self, settings: Settings) -> None:
+        self._settings = settings
+        self._pool: Pool | None = None
+
+    @property
+    def pool(self) -> Pool:
+        """Return the initialized pool to repository factories."""
+
+        if self._pool is None:
+            message = "database pool is not initialized"
+            raise RuntimeError(message)
+        return self._pool
+
+    async def connect(self) -> None:
+        """Create the pool and verify the first connection."""
+
+        if self._pool is not None:
+            return
+        settings = self._settings
+        pool = await asyncpg.create_pool(
+            dsn=settings.database_url.get_secret_value(),
+            min_size=settings.db_pool_min_size,
+            max_size=settings.db_pool_max_size,
+            timeout=settings.db_connect_timeout_seconds,
+            command_timeout=settings.db_command_timeout_seconds,
+        )
+        if pool is None:  # pragma: no cover - asyncpg types allow this for legacy reasons
+            message = "asyncpg did not create a pool"
+            raise RuntimeError(message)
+        self._pool = cast(Pool, pool)
+
+    async def close(self) -> None:
+        """Close all pooled connections; repeated close is safe."""
+
+        pool, self._pool = self._pool, None
+        if pool is not None:
+            await pool.close()
+
+    async def is_ready(self) -> bool:
+        """Check that PostgreSQL accepts a trivial query."""
+
+        if self._pool is None:
+            return False
+        try:
+            return bool(await self._pool.fetchval("SELECT 1") == 1)
+        except asyncpg.PostgresError:
+            return False
+
+    async def __aenter__(self) -> Self:
+        await self.connect()
+        return self
+
+    async def __aexit__(self, exc_type: object, exc: object, traceback: object) -> None:
+        await self.close()

app/dependencies.py

@@ -0,0 +1,14 @@
+"""FastAPI dependency adapters."""
+
+from __future__ import annotations
+
+from fastapi import Request
+
+from app.db.pool import Database
+
+
+def get_database(request: Request) -> Database:
+    """Resolve the lifespan-owned database from application state."""
+
+    database: Database = request.app.state.database
+    return database

app/lifespan.py

@@ -0,0 +1,36 @@
+"""Application resource ownership."""
+
+from __future__ import annotations
+
+from collections.abc import AsyncIterator, Callable
+from contextlib import AbstractAsyncContextManager, asynccontextmanager
+
+from fastapi import FastAPI
+
+from app.config import Settings
+from app.db.pool import AsyncpgDatabase, Database
+
+DatabaseFactory = Callable[[Settings], Database]
+Lifespan = Callable[[FastAPI], AbstractAsyncContextManager[None]]
+
+
+def create_lifespan(settings: Settings, database_factory: DatabaseFactory) -> Lifespan:
+    """Build a lifespan context so tests can inject a database implementation."""
+
+    @asynccontextmanager
+    async def lifespan(app: FastAPI) -> AsyncIterator[None]:
+        database = database_factory(settings)
+        await database.connect()
+        app.state.database = database
+        try:
+            yield
+        finally:
+            await database.close()
+
+    return lifespan
+
+
+def default_database_factory(settings: Settings) -> Database:
+    """Create the production asyncpg adapter."""
+
+    return AsyncpgDatabase(settings)

app/logging.py

@@ -0,0 +1,40 @@
+"""Structured logging configuration with safe JSON output."""
+
+from __future__ import annotations
+
+import json
+import logging
+from datetime import UTC, datetime
+from typing import Any
+
+
+class JsonFormatter(logging.Formatter):
+    """Serialize standard records and selected structured attributes as JSON."""
+
+    _fields = ("request_id", "method", "path", "status", "duration_ms")
+
+    def format(self, record: logging.LogRecord) -> str:
+        payload: dict[str, Any] = {
+            "timestamp": datetime.now(UTC).isoformat(),
+            "level": record.levelname,
+            "logger": record.name,
+            "message": record.getMessage(),
+        }
+        for field in self._fields:
+            value = getattr(record, field, None)
+            if value is not None:
+                payload[field] = value
+        if record.exc_info is not None:
+            payload["exception"] = self.formatException(record.exc_info)
+        return json.dumps(payload, ensure_ascii=False, separators=(",", ":"))
+
+
+def configure_logging(level: str) -> None:
+    """Configure the root logger once for the process."""
+
+    handler = logging.StreamHandler()
+    handler.setFormatter(JsonFormatter())
+    root = logging.getLogger()
+    root.handlers.clear()
+    root.addHandler(handler)
+    root.setLevel(level.upper())

app/main.py

@@ -0,0 +1,34 @@
+"""FastAPI application factory and ASGI entry point."""
+
+from __future__ import annotations
+
+from fastapi import FastAPI
+
+from app.api.errors import unhandled_exception_handler
+from app.api.middleware import RequestContextMiddleware
+from app.config import Settings, get_settings
+from app.lifespan import DatabaseFactory, create_lifespan, default_database_factory
+from app.logging import configure_logging
+from app.observability.health import router as health_router
+
+
+def create_app(
+    settings: Settings | None = None,
+    database_factory: DatabaseFactory = default_database_factory,
+) -> FastAPI:
+    """Create an isolated application instance with explicit resource factories."""
+
+    resolved = settings or get_settings()
+    configure_logging(resolved.log_level)
+    app = FastAPI(
+        title=resolved.app_name,
+        version="0.0.1",
+        lifespan=create_lifespan(resolved, database_factory),
+    )
+    app.add_middleware(RequestContextMiddleware, header_name=resolved.request_id_header)
+    app.add_exception_handler(Exception, unhandled_exception_handler)
+    app.include_router(health_router)
+    return app
+
+
+app = create_app()

app/observability/__init__.py

@@ -0,0 +1 @@
+"""Health, metrics, and tracing adapters."""

app/observability/health.py

@@ -0,0 +1,37 @@
+"""Kubernetes-compatible health endpoints."""
+
+from __future__ import annotations
+
+from typing import Annotated
+
+from fastapi import APIRouter, Depends, Response, status
+from pydantic import BaseModel
+
+from app.db.pool import Database
+from app.dependencies import get_database
+
+router = APIRouter(prefix="/health", tags=["health"])
+
+
+class HealthResponse(BaseModel):
+    status: str
+
+
+@router.get("/live", response_model=HealthResponse)
+async def live() -> HealthResponse:
+    """Report process liveness without checking dependencies."""
+
+    return HealthResponse(status="ok")
+
+
+@router.get("/ready", response_model=HealthResponse)
+async def ready(
+    response: Response,
+    database: Annotated[Database, Depends(get_database)],
+) -> HealthResponse:
+    """Report whether the required database dependency is usable."""
+
+    if await database.is_ready():
+        return HealthResponse(status="ok")
+    response.status_code = status.HTTP_503_SERVICE_UNAVAILABLE
+    return HealthResponse(status="unavailable")