backend/app/main.py

from collections.abc import AsyncIterator
from contextlib import asynccontextmanager
from pathlib import Path

from fastapi import FastAPI
from fastapi.responses import FileResponse
from fastapi.staticfiles import StaticFiles

from app.api.routes import create_router
from app.core.config import get_settings
from app.db.database import create_session_factory, init_db
from app.db.repository import Repository


def _configure_pipeline_api(app: FastAPI) -> None:
    if getattr(app.state, "pipeline_api_configured", False):
        return
    settings = get_settings()
    settings.data_dir.mkdir(parents=True, exist_ok=True)
    engine, session_factory = create_session_factory(settings.database_url)
    init_db(engine)
    repo = Repository(session_factory)
    app.include_router(create_router(repo))
    _prioritize_api_routes(app)
    app.state.pipeline_api_configured = True


def _prioritize_api_routes(app: FastAPI) -> None:
    app.router.routes.sort(
        key=lambda route: 0 if getattr(route, "path", "").startswith("/api") else 1
    )


def _configure_frontend(app: FastAPI) -> None:
    settings = get_settings()
    frontend_dir = settings.frontend_dir
    if frontend_dir is None:
        return

    index_html = frontend_dir / "index.html"
    assets_dir = frontend_dir / "assets"
    if assets_dir.exists():
        app.mount("/assets", StaticFiles(directory=assets_dir), name="assets")
    if not index_html.exists():
        return

    @app.get("/")
    def frontend_index() -> FileResponse:
        return FileResponse(index_html)

    @app.get("/{path:path}", include_in_schema=False)
    def frontend_fallback(path: str) -> FileResponse:
        candidate = _safe_frontend_file(frontend_dir, path)
        if candidate is not None and candidate.exists() and candidate.is_file():
            return FileResponse(candidate)
        return FileResponse(index_html)


def _safe_frontend_file(frontend_dir: Path, path: str) -> Path | None:
    if not path or path.startswith("api/"):
        return None
    root = frontend_dir.resolve()
    candidate = (root / path).resolve()
    if root == candidate or root in candidate.parents:
        return candidate
    return None


@asynccontextmanager
async def lifespan(app: FastAPI) -> AsyncIterator[None]:
    _configure_pipeline_api(app)
    yield


def create_app(*, initialize: bool = True) -> FastAPI:
    app = FastAPI(
        title="Fast Follow Structure Generator",
        lifespan=None if initialize else lifespan,
    )

    @app.get("/health")
    def health() -> dict[str, str]:
        return {"status": "ok"}

    if initialize:
        _configure_pipeline_api(app)
    _configure_frontend(app)
    return app


app = create_app(initialize=False)