LLeMbas/src/lembas/main.py

"""Application factory, lifespan and error handling."""

from __future__ import annotations

import logging
from collections.abc import AsyncIterator
from contextlib import asynccontextmanager

from fastapi import FastAPI, Request, status
from fastapi.responses import JSONResponse, Response
from fastapi.staticfiles import StaticFiles
from starlette.exceptions import HTTPException as StarletteHTTPException

from lembas import __version__
from lembas.api import (
    admin,
    admin_models,
    admin_users,
    auth,
    chats,
    folders,
    pages,
    preferences,
)
from lembas.api.deps import RedirectToLogin, is_htmx, login_redirect
from lembas.config import settings
from lembas.db.session import init_db
from lembas.web.templating import STATIC_DIR, render

log = logging.getLogger("lembas")


def configure_logging() -> None:
    logging.basicConfig(
        level=settings.log_level.upper(),
        format="%(asctime)s  %(levelname)-7s %(name)s: %(message)s",
        datefmt="%H:%M:%S",
    )


@asynccontextmanager
async def lifespan(app: FastAPI) -> AsyncIterator[None]:
    configure_logging()
    settings.ensure_dirs()
    init_db()

    if settings.secret_key_is_ephemeral:
        log.warning(
            "No LEMBAS_SECRET_KEY set, so a temporary one was generated. Every "
            "restart will sign all users out and make stored API keys "
            "unreadable. Generate a permanent key with:\n"
            '    python -c "import secrets; print(secrets.token_urlsafe(48))"'
        )

    log.info("LLeMbas %s starting on http://%s:%s", __version__, settings.host, settings.port)
    log.info("data directory: %s", settings.data_dir.resolve())
    yield
    log.info("LLeMbas stopped")


def create_app() -> FastAPI:
    app = FastAPI(
        title="LLeMbas",
        version=__version__,
        lifespan=lifespan,
        # The API is an implementation detail of the UI, not a product surface.
        docs_url="/api/docs" if settings.log_level == "debug" else None,
        redoc_url=None,
    )

    app.mount("/static", StaticFiles(directory=str(STATIC_DIR)), name="static")

    app.include_router(pages.router)
    app.include_router(auth.router)
    app.include_router(preferences.router)
    app.include_router(chats.router)
    app.include_router(folders.router)
    app.include_router(admin.router)
    app.include_router(admin_users.router)
    app.include_router(admin_models.router)

    register_error_handlers(app)
    return app


def register_error_handlers(app: FastAPI) -> None:
    @app.exception_handler(RedirectToLogin)
    async def _not_signed_in(request: Request, exc: RedirectToLogin) -> Response:
        # An htmx request must not swap a login page into a fragment of the
        # chat UI, so tell the browser to navigate instead.
        if is_htmx(request):
            response = Response(status_code=status.HTTP_204_NO_CONTENT)
            response.headers["HX-Redirect"] = "/auth/login"
            return response
        return login_redirect(exc.next_url)

    @app.exception_handler(StarletteHTTPException)
    async def _http_error(request: Request, exc: StarletteHTTPException) -> Response:
        # JSON callers and htmx fragments want the bare status; humans loading a
        # page want a themed page they can navigate away from.
        wants_page = "text/html" in request.headers.get("accept", "") and not is_htmx(request)
        if not wants_page:
            return JSONResponse({"detail": exc.detail}, status_code=exc.status_code)

        return render(
            request,
            "error.html",
            {
                "status_code": exc.status_code,
                "detail": exc.detail,
                "flavour": ERROR_FLAVOUR.get(exc.status_code, ERROR_FLAVOUR[500]),
            },
            status_code=exc.status_code,
        )

    @app.exception_handler(Exception)
    async def _unhandled(request: Request, exc: Exception) -> Response:
        log.exception("unhandled error at %s", request.url.path)
        if is_htmx(request) or "text/html" not in request.headers.get("accept", ""):
            return JSONResponse({"detail": "Internal server error"}, status_code=500)
        return render(
            request,
            "error.html",
            {"status_code": 500, "detail": "Something went wrong.",
             "flavour": ERROR_FLAVOUR[500]},
            status_code=500,
        )


# Flavour lives in error pages, empty states and theme names -- never in the
# functional UI. See CLAUDE.md.
ERROR_FLAVOUR = {
    403: "Speak, friend, and enter. This door is not yours to open.",
    404: "Not all those who wander are lost. This page, however, is.",
    500: "The Road goes ever on, but this stretch of it has washed out.",
}


app = create_app()