"""PostGenerator FastAPI application.

IMPORTANT: root_path is intentionally NOT set in the FastAPI() constructor.
It is passed only via Uvicorn's --root-path flag at runtime to avoid the
double-path bug (Pitfall #4).
"""

from contextlib import asynccontextmanager
from pathlib import Path

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

from backend.config import CAMPAIGNS_PATH, CONFIG_PATH, OUTPUTS_PATH, PROMPTS_PATH


# ---------------------------------------------------------------------------
# SPA static files with catch-all fallback
# ---------------------------------------------------------------------------

class SPAStaticFiles(StaticFiles):
    """Serve a React SPA: return index.html for any 404 so the client-side
    router handles unknown paths instead of returning a 404 from the server."""

    async def get_response(self, path: str, scope):
        try:
            return await super().get_response(path, scope)
        except Exception:
            # Fall back to index.html for client-side routing
            return await super().get_response("index.html", scope)


# ---------------------------------------------------------------------------
# Startup / shutdown lifecycle
# ---------------------------------------------------------------------------

@asynccontextmanager
async def lifespan(app: FastAPI):
    """Create required data directories on startup if they do not exist."""
    for directory in (PROMPTS_PATH, OUTPUTS_PATH, CAMPAIGNS_PATH, CONFIG_PATH):
        directory.mkdir(parents=True, exist_ok=True)
    yield
    # Nothing to clean up on shutdown


# ---------------------------------------------------------------------------
# Application
# ---------------------------------------------------------------------------

# CRITICAL: Do NOT pass root_path here — use Uvicorn --root-path instead.
app = FastAPI(
    title="PostGenerator",
    description="Instagram carousel post generator powered by Claude",
    version="0.1.0",
    lifespan=lifespan,
    # root_path is intentionally absent — set via Uvicorn --root-path at runtime
)


# ---------------------------------------------------------------------------
# API routes (must be registered BEFORE the SPA catch-all mount)
# ---------------------------------------------------------------------------

@app.get("/api/health")
async def health() -> dict:
    """Health check endpoint."""
    return {"status": "ok"}


# ---------------------------------------------------------------------------
# SPA catch-all mount (MUST be last — catches everything not matched above)
# ---------------------------------------------------------------------------

_STATIC_DIR = Path(__file__).parent.parent / "static"

if _STATIC_DIR.exists():
    app.mount("/", SPAStaticFiles(directory=str(_STATIC_DIR), html=True), name="spa")