rebuild(stage-1): establish isolated application skeleton

next/backend/bootstrap/__init__.py

@@ -0,0 +1 @@
+"""Application composition root."""

next/backend/bootstrap/application.py

@@ -0,0 +1,19 @@
+from fastapi import FastAPI
+
+from backend.bootstrap.settings import Settings
+from backend.http.errors import install_error_handlers
+from backend.http.router import api_router
+
+
+def create_application(settings: Settings | None = None) -> FastAPI:
+    runtime = settings or Settings.from_environment()
+    application = FastAPI(
+        title="小白复盘",
+        version="0.1.0",
+        docs_url="/api/docs" if runtime.debug else None,
+        redoc_url=None,
+    )
+    application.state.settings = runtime
+    install_error_handlers(application)
+    application.include_router(api_router, prefix="/api")
+    return application

next/backend/bootstrap/settings.py

@@ -0,0 +1,22 @@
+from __future__ import annotations
+
+import os
+from dataclasses import dataclass
+from pathlib import Path
+
+
+@dataclass(frozen=True, slots=True)
+class Settings:
+    environment: str
+    debug: bool
+    data_directory: Path
+
+    @classmethod
+    def from_environment(cls) -> Settings:
+        environment = os.getenv("APP_ENV", "development").strip().lower()
+        data_directory = Path(os.getenv("APP_DATA_DIR", "data")).resolve()
+        return cls(
+            environment=environment,
+            debug=environment == "development",
+            data_directory=data_directory,
+        )