from __future__ import annotations

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

from fastapi import FastAPI
from starlette.concurrency import run_in_threadpool
from starlette.middleware.trustedhost import TrustedHostMiddleware

from .ddns_dns import DnsConfigurationError, DnsProviderError, DnsReconciliationError, delete_dns_records, publish_dns
from .ddns_models import DdnsSettings, UpdateResult
from .ddns_service import DdnsService
from .ddns_store import DdnsStore
from .routers import admin, api, assets, management, public, updates
from .web.security_headers import RequestBodyLimitMiddleware, install_security_middleware

__all__ = [
    "DdnsSettings",
    "DdnsStore",
    "DnsConfigurationError",
    "DnsProviderError",
    "DnsReconciliationError",
    "UpdateResult",
    "delete_dns_records",
    "make_app",
    "publish_dns",
]


OPENAPI_TAGS = [
    {
        "name": "hostnames",
        "description": "Create KarlDNS hostnames or hostnames under verified domains.",
    },
    {
        "name": "domains",
        "description": "Issue and verify DNS TXT challenges for custom domains.",
    },
    {
        "name": "updates",
        "description": "Router-facing IP update endpoints for FRITZ!Box and compatible clients.",
    },
    {
        "name": "management",
        "description": "API management through private dashboard links. Dashboard passwords protect only the web dashboard, not these API routes.",
    },
]

CLEANUP_TASK_NAME = "cleanup"
RATE_LIMIT_FLUSH_INTERVAL_SECONDS = 10
LOGGER = logging.getLogger(__name__)


def make_app(settings: DdnsSettings | None = None) -> FastAPI:
    settings = settings or DdnsSettings.from_env()
    settings.validate_launch_ready()

    store = DdnsStore(settings.database_path)
    store.ensure_scheduled_task(CLEANUP_TASK_NAME, settings.cleanup_interval_seconds)
    store.optimize()
    service = DdnsService(settings, store)

    @asynccontextmanager
    async def lifespan(_: FastAPI) -> AsyncIterator[None]:
        cleanup_task = asyncio.create_task(_scheduler_loop(store, settings))
        rate_limit_task = asyncio.create_task(_rate_limit_flush_loop(store))
        try:
            yield
        finally:
            cleanup_task.cancel()
            rate_limit_task.cancel()
            with contextlib.suppress(asyncio.CancelledError):
                await cleanup_task
            with contextlib.suppress(asyncio.CancelledError):
                await rate_limit_task
            await run_in_threadpool(store.flush_rate_limits)
            await run_in_threadpool(store.close_connections)

    app = FastAPI(
        title="KarlDNS",
        summary="A small self-hosted DynDNS provider for FRITZ!Box routers.",
        description=(
            "Generate cryptographically random DynDNS endpoints, verify custom domains with DNS TXT "
            "records, and publish A/AAAA records through Cloudflare or RFC 2136."
        ),
        version="0.1.0",
        docs_url="/docs",
        redoc_url="/redoc",
        openapi_tags=OPENAPI_TAGS,
        lifespan=lifespan,
    )
    app.add_middleware(TrustedHostMiddleware, allowed_hosts=settings.effective_trusted_hosts)
    app.add_middleware(RequestBodyLimitMiddleware, max_body_bytes=settings.max_request_body_bytes)
    app.state.settings = settings
    app.state.store = store
    app.state.service = service
    install_security_middleware(app, settings, store)
    app.include_router(api.router)
    app.include_router(assets.router)
    app.include_router(public.router)
    app.include_router(management.router)
    app.include_router(admin.make_router(settings.admin_path))
    app.include_router(updates.router)
    return app


async def _scheduler_loop(store: DdnsStore, settings: DdnsSettings) -> None:
    poll_seconds = min(settings.cleanup_interval_seconds, 60)
    while True:
        await _run_cleanup_if_due(store, settings)
        await asyncio.sleep(poll_seconds)


async def _rate_limit_flush_loop(store: DdnsStore) -> None:
    while True:
        await asyncio.sleep(RATE_LIMIT_FLUSH_INTERVAL_SECONDS)
        await run_in_threadpool(store.flush_rate_limits)
        await run_in_threadpool(store.prune_rate_limit_storage)
        await run_in_threadpool(store.checkpoint_wal)


async def _run_cleanup_if_due(store: DdnsStore, settings: DdnsSettings) -> None:
    lease_owner = f"{os.getpid()}:{id(store)}"
    lease_seconds = max(60, settings.cleanup_interval_seconds)
    acquired = await run_in_threadpool(
        store.acquire_due_task,
        CLEANUP_TASK_NAME,
        lease_owner,
        lease_seconds,
    )
    if not acquired:
        return
    try:
        await run_in_threadpool(
            store.cleanup,
            settings.cleanup_challenge_hours,
            settings.cleanup_unused_account_hours,
            settings.cleanup_event_history_hours,
        )
    except Exception as exc:
        LOGGER.exception("Scheduled cleanup failed")
        await run_in_threadpool(store.increment_metric, "cleanup_errors_total")
        await run_in_threadpool(
            store.complete_scheduled_task,
            CLEANUP_TASK_NAME,
            settings.cleanup_interval_seconds,
            False,
            f"{type(exc).__name__}: {exc}",
        )
        return
    await run_in_threadpool(
        store.complete_scheduled_task,
        CLEANUP_TASK_NAME,
        settings.cleanup_interval_seconds,
        True,
        "",
    )
    await run_in_threadpool(store.increment_metric, "cleanup_success_total")
    await run_in_threadpool(store.optimize)