"""
app.py — LibBee v3.5
FastAPI entry point: CORS, middleware, lifespan, router mounting.

Changes over v3.1:
- Maintenance mode middleware now reads from JsonRuntimeStore (admin-editable)
  instead of settings.maintenance_mode (env var, static at startup).
- CORS origins updated: added ku-library.github.io.
- Section headers added throughout.
"""

# ── Imports ────────────────────────────────────────────────────────────────────

import asyncio
import logging
import time
from contextlib import asynccontextmanager

from fastapi import FastAPI, Request
from fastapi.middleware.cors import CORSMiddleware
from fastapi.responses import JSONResponse

try:
    from cachetools import TTLCache
    _ttl_cache_available = True
except ImportError:
    _ttl_cache_available = False

from src.config import get_settings, LIBBEE_VERSION
from src.services.cache_service import CacheService
from src.services.metrics_service import MetricsService
from src.services.rag_service import RAGService

logging.basicConfig(level=logging.INFO)
logger = logging.getLogger(__name__)


# ── Service Instances ──────────────────────────────────────────────────────────

rag_service     = RAGService()
cache_service   = CacheService()
metrics_service = MetricsService(get_settings().metrics_path)


# ── Rate-limit Request Log ─────────────────────────────────────────────────────
# TTLCache auto-evicts entries older than ttl seconds.
# Falls back to a plain deque-based dict if cachetools is not installed.

if _ttl_cache_available:
    _request_log      = TTLCache(maxsize=10_000, ttl=120)
    _request_log_lock = asyncio.Lock()
else:
    from collections import defaultdict, deque
    _request_log      = defaultdict(deque)   # type: ignore[assignment]
    _request_log_lock = asyncio.Lock()


# ── Public Accessors ───────────────────────────────────────────────────────────
# Routers import these instead of importing module-level globals directly,
# which avoids circular-import issues at import time.

def get_rag_service() -> RAGService:
    return rag_service


def get_metrics_service() -> MetricsService:
    return metrics_service


# ── Background Tasks ───────────────────────────────────────────────────────────

async def _metrics_flush_loop(interval: int = 30) -> None:
    """Flush in-memory metric counters to disk every `interval` seconds."""
    while True:
        await asyncio.sleep(interval)
        try:
            await metrics_service.flush()
        except Exception as exc:
            logger.warning("Metrics flush error: %s", exc)


# ── Lifespan ───────────────────────────────────────────────────────────────────

@asynccontextmanager
async def lifespan(app: FastAPI):
    from src.services.staff_service import build_staff_index

    settings = get_settings()

    # Build staff index
    try:
        build_staff_index()
        logger.info("Staff index built")
    except Exception as exc:
        logger.error("Staff index build failed: %s", exc)

    # Initialise RAG service
    if settings.openai_api_key:
        try:
            await rag_service.initialize(openai_api_key=settings.openai_api_key)
            logger.info("RAG service ready — chunks: %d", len(rag_service.bm25_corpus))
        except Exception as exc:
            logger.error("RAG initialization failed: %s", exc, exc_info=True)
    else:
        logger.warning("OPENAI_API_KEY not set — RAG disabled")

    # Start background metrics flush
    flush_task = asyncio.create_task(_metrics_flush_loop(interval=30))
    logger.info("LibBee startup complete")

    yield

    # Graceful shutdown — flush remaining metrics
    flush_task.cancel()
    try:
        await asyncio.wait_for(metrics_service.flush(), timeout=5.0)
    except Exception:
        pass
    logger.info("LibBee shutting down")


# ── FastAPI App ────────────────────────────────────────────────────────────────

app = FastAPI(
    title="LibBee - KU Library AI",
    description="Khalifa University Library AI Assistant",
    version=LIBBEE_VERSION,
    lifespan=lifespan,
)


# ── CORS Middleware ────────────────────────────────────────────────────────────

app.add_middleware(
    CORSMiddleware,
    allow_origins=[
        "https://nikeshn.github.io",
        "https://ku-library.github.io",       # added v3.5
        "http://localhost:8080",
        "http://localhost:3000",
        "http://127.0.0.1:5500",
    ],
    allow_credentials=True,
    allow_methods=["GET", "POST", "PUT", "DELETE", "OPTIONS"],
    allow_headers=["*"],
    max_age=86400,
)


# ── Operational Guardrails Middleware ──────────────────────────────────────────

@app.middleware("http")
async def security_headers(request: Request, call_next):
    """
    Add security headers to every response.
    X-Content-Type-Options — prevents MIME sniffing
    X-Frame-Options        — prevents clickjacking
    Referrer-Policy        — limits referrer leakage
    X-XSS-Protection       — legacy XSS filter (belt-and-braces)
    Permissions-Policy     — disables unused browser features
    """
    response = await call_next(request)
    response.headers["X-Content-Type-Options"]  = "nosniff"
    response.headers["X-Frame-Options"]          = "SAMEORIGIN"
    response.headers["Referrer-Policy"]          = "strict-origin-when-cross-origin"
    response.headers["X-XSS-Protection"]         = "1; mode=block"
    response.headers["Permissions-Policy"]       = (
        "geolocation=(), microphone=(), camera=(), payment=()"
    )
    return response


@app.middleware("http")
async def operational_guardrails(request: Request, call_next):
    settings = get_settings()

    # ── Maintenance mode ───────────────────────────────────────────────────────
    # FIX v3.5: read from JsonRuntimeStore (admin-editable) rather than
    # settings.maintenance_mode (env var, static at startup). This means
    # toggling maintenance via the admin dashboard actually takes effect.
    _maintenance_on = False
    try:
        from src.services.runtime_store import JsonRuntimeStore
        _store = JsonRuntimeStore(settings.config_path, default={"maintenance_mode": False})
        _maintenance_on = bool(_store.load().get("maintenance_mode", False))
    except Exception:
        # If store is unreadable fall back to env-var setting
        _maintenance_on = settings.maintenance_mode

    _exempt_paths = {"/", "/config", "/admin", "/admin/login", "/admin/auth"}
    if _maintenance_on and request.url.path not in _exempt_paths:
        return JSONResponse(
            status_code=503,
            content={"detail": "LibBee is in maintenance mode. Please try again shortly."},
        )

    # ── Rate limiting ──────────────────────────────────────────────────────────
    client_ip = request.client.host if request.client else "unknown"
    now = time.time()

    async with _request_log_lock:
        if _ttl_cache_available:
            timestamps = _request_log.get(client_ip, [])
            timestamps = [t for t in timestamps if now - t < 60]
            if len(timestamps) >= settings.rate_limit_per_minute:
                metrics_service.incr_bucket("errors", "rate_limit")
                return JSONResponse(
                    status_code=429,
                    content={"detail": "Too many requests. Please slow down and try again."},
                )
            timestamps.append(now)
            _request_log[client_ip] = timestamps
        else:
            from collections import deque
            bucket = _request_log[client_ip]  # type: ignore[index]
            while bucket and now - bucket[0] > 60:
                bucket.popleft()
            if len(bucket) >= settings.rate_limit_per_minute:
                metrics_service.incr_bucket("errors", "rate_limit")
                return JSONResponse(
                    status_code=429,
                    content={"detail": "Too many requests. Please slow down and try again."},
                )
            bucket.append(now)

    # ── Request execution ──────────────────────────────────────────────────────
    try:
        response = await call_next(request)
        return response
    except Exception as exc:
        logger.exception("Unhandled application error: %s", exc)
        metrics_service.incr_bucket("errors", "unhandled_exception")
        return JSONResponse(status_code=500, content={"detail": "Unexpected server error."})


# ── Router Mounting ────────────────────────────────────────────────────────────

from src.api import admin, agent, feedback, search  # noqa: E402

app.include_router(agent.router,    prefix="/agent",    tags=["Agent"])
app.include_router(search.router,   prefix="/search",   tags=["Search"])
app.include_router(admin.router,    prefix="/admin",    tags=["Admin"])
app.include_router(feedback.router, prefix="/feedback", tags=["Feedback"])


# ── Health & Public Endpoints ──────────────────────────────────────────────────

@app.get("/favicon.ico", include_in_schema=False)
async def favicon():
    """
    Return 204 No Content for favicon requests.
    Prevents 404 errors in browser console — the backend has no favicon,
    the frontend (GitHub Pages) serves its own at assets/libbee-mascot.png.
    """
    from fastapi.responses import Response
    return Response(status_code=204)


@app.get("/")
def health_check():
    settings = get_settings()
    return {
        "status": "ok",
        "version": LIBBEE_VERSION,
        "service": "LibBee KU Library AI",
        "rag_ready": rag_service.is_ready(),
        "maintenance_mode": settings.maintenance_mode,
        "endpoints": ["/agent", "/search", "/admin", "/feedback"],
    }


@app.get("/config")
def public_config():
    """Legacy public config endpoint — frontend uses /admin/public-config instead."""
    settings = get_settings()
    return {
        "welcome_message": "Hi! I'm LibBee, the Khalifa University Library AI Assistant.",
        "max_results": settings.max_results,
        "maintenance_mode": settings.maintenance_mode,
    }


@app.get("/year")
def get_year():
    from datetime import datetime
    now = datetime.utcnow()
    return {"year": now.year, "month": now.month, "date": now.strftime("%Y-%m-%d")}