"""Aurora Core FastAPI application factory.

Stateless by design (section 1): nothing here holds request-scoped state in
process memory, so any number of API replicas can run behind Traefik.
"""

from __future__ import annotations

import time
import uuid
from collections.abc import Awaitable, Callable
from contextlib import asynccontextmanager
from pathlib import Path

from fastapi import FastAPI, Request, Response
from fastapi.exceptions import RequestValidationError
from fastapi.middleware.cors import CORSMiddleware
from fastapi.responses import JSONResponse
from fastapi.staticfiles import StaticFiles
from prometheus_client import CONTENT_TYPE_LATEST, Counter, Histogram, generate_latest
from starlette.exceptions import HTTPException as StarletteHTTPException

from app.api.v1 import (
    admin,
    collections,
    companies,
    episodes,
    health,
    movies,
    people,
    search,
    seasons,
    series,
)
from app.core.config import get_settings
from app.core.database import dispose_engine
from app.core.logging import configure_logging, get_logger, request_id_ctx
from app.core.queue import close_arq_pool
from app.core.redis import close_redis

settings = get_settings()

REQUEST_COUNT = Counter(
    "aurora_http_requests_total", "HTTP requests", ["method", "path", "status"]
)
REQUEST_LATENCY = Histogram(
    "aurora_http_request_duration_seconds", "HTTP request latency", ["method", "path"]
)

MAX_REQUEST_BODY_BYTES = 2 * 1024 * 1024  # 2 MiB


@asynccontextmanager
async def lifespan(app: FastAPI):
    configure_logging()
    logger = get_logger(__name__)
    logger.info("aurora_core_starting", env=settings.AURORA_ENV)
    yield
    logger.info("aurora_core_stopping")
    await dispose_engine()
    await close_redis()
    await close_arq_pool()


app = FastAPI(
    title="Aurora Core",
    description="Aurora Dragon Studio's media metadata, discovery, and intelligence backend.",
    version="0.1.0",
    docs_url=settings.docs_url,
    redoc_url=None,
    openapi_url=settings.openapi_url,
    lifespan=lifespan,
)

app.add_middleware(
    CORSMiddleware,
    allow_origins=settings.cors_origins_list,
    allow_credentials=True,
    allow_methods=["GET", "POST"],
    allow_headers=["*"],
)

# Serves what app/services/artwork/ downloads (section 10: self-hosted
# artwork). The directory must exist before StaticFiles will mount — the
# worker creates subdirectories as it writes files, but the root itself
# needs to be there even before the first download.
Path(settings.MEDIA_ROOT).mkdir(parents=True, exist_ok=True)
app.mount(
    settings.MEDIA_URL_PREFIX,
    StaticFiles(directory=settings.MEDIA_ROOT),
    name="media",
)


@app.middleware("http")
async def request_context_middleware(
    request: Request, call_next: Callable[[Request], Awaitable[Response]]
) -> Response:
    request_id = request.headers.get("X-Request-ID", str(uuid.uuid4()))
    token = request_id_ctx.set(request_id)
    start = time.perf_counter()
    try:
        response = await call_next(request)
    finally:
        request_id_ctx.reset(token)

    duration = time.perf_counter() - start
    route = request.scope.get("route")
    path_template = route.path if route else request.url.path
    REQUEST_COUNT.labels(request.method, path_template, "n/a").inc()
    REQUEST_LATENCY.labels(request.method, path_template).observe(duration)

    response.headers["X-Request-ID"] = request_id
    response.headers["X-Content-Type-Options"] = "nosniff"
    response.headers["X-Frame-Options"] = "DENY"
    response.headers["Referrer-Policy"] = "no-referrer"
    return response


@app.middleware("http")
async def request_size_limit_middleware(
    request: Request, call_next: Callable[[Request], Awaitable[Response]]
) -> Response:
    content_length = request.headers.get("content-length")
    if content_length and int(content_length) > MAX_REQUEST_BODY_BYTES:
        return JSONResponse(
            status_code=413,
            content={"error": {"code": "payload_too_large", "message": "Request body too large."}},
        )
    return await call_next(request)


@app.exception_handler(StarletteHTTPException)
async def http_exception_handler(request: Request, exc: StarletteHTTPException) -> JSONResponse:
    detail = exc.detail
    if isinstance(detail, dict) and "code" in detail:
        error = detail
    else:
        error = {"code": "http_error", "message": str(detail)}
    return JSONResponse(status_code=exc.status_code, content={"error": error})


@app.exception_handler(RequestValidationError)
async def validation_exception_handler(
    request: Request, exc: RequestValidationError
) -> JSONResponse:
    return JSONResponse(
        status_code=422,
        content={
            "error": {
                "code": "validation_error",
                "message": "Request validation failed.",
                "details": exc.errors(),
            }
        },
    )


@app.get("/metrics", include_in_schema=False)
async def metrics() -> Response:
    return Response(generate_latest(), media_type=CONTENT_TYPE_LATEST)


# Unversioned liveness/readiness for infra probes (Docker/Traefik healthchecks).
app.include_router(health.router)

API_V1_PREFIX = "/api/v1"
app.include_router(health.router, prefix=API_V1_PREFIX)
app.include_router(search.router, prefix=API_V1_PREFIX)
app.include_router(movies.router, prefix=API_V1_PREFIX)
app.include_router(series.router, prefix=API_V1_PREFIX)
app.include_router(seasons.router, prefix=API_V1_PREFIX)
app.include_router(episodes.router, prefix=API_V1_PREFIX)
app.include_router(people.router, prefix=API_V1_PREFIX)
app.include_router(collections.router, prefix=API_V1_PREFIX)
app.include_router(companies.router, prefix=API_V1_PREFIX)
app.include_router(admin.router, prefix=API_V1_PREFIX)