"""Application startup helpers.

This module contains shared startup logic extracted from ``app.main`` so that
initialisation is easier to reason about and unit test. The lifespan handler
in ``app.main`` delegates resource creation and task registration here.
"""

from __future__ import annotations

import os
from contextlib import suppress
from pathlib import Path
from typing import TYPE_CHECKING

import aiohttp
import structlog
from apscheduler.schedulers.asyncio import AsyncIOScheduler  # type: ignore[import-untyped]

from app.db import init_db, open_db
from app.services import setup_service
from app.services.geo_cache import GeoCache
from app.tasks import blocklist_import, geo_cache_flush, geo_re_resolve, health_check, history_sync
from app.utils.async_utils import run_blocking
from app.utils.jail_config import ensure_jail_configs
from app.utils.runtime_state import set_runtime_settings
from app.utils.setup_state import set_setup_complete_cache

if TYPE_CHECKING:
    from fastapi import FastAPI

    from app.config import Settings

log: structlog.stdlib.BoundLogger = structlog.get_logger()


def _check_single_worker_mode() -> None:
    """Verify that the application is running with a single worker.

    APScheduler's AsyncIOScheduler is bound to a single asyncio event loop
    and cannot be safely shared across multiple worker processes. If each
    worker starts its own scheduler instance, all background jobs execute N
    times (where N is the number of workers), resulting in duplicate blocklist
    imports, duplicate ban operations, duplicate history writes, and SQLite
    lock contention.

    This function detects multi-worker configurations and raises a clear
    RuntimeError with instructions.

    Raises:
        RuntimeError: If the app would run with multiple workers.
    """
    # Check for explicit worker count env var (convention used in deployment)
    workers_env = os.environ.get("BANGUI_WORKERS")
    if workers_env is not None:
        try:
            worker_count = int(workers_env)
            if worker_count > 1:
                raise RuntimeError(
                    "BanGUI background scheduler cannot run with multiple workers.\n"
                    f"BANGUI_WORKERS is set to {worker_count}. Set it to 1 or remove it.\n"
                    "See Architekture.md § Deployment Constraints for details."
                )
        except ValueError as e:
            raise RuntimeError(
                f"BANGUI_WORKERS environment variable must be an integer, got: {workers_env}"
            ) from e


async def _ensure_database_schema(database_path: str) -> None:
    """Create the configured runtime database if it does not already exist."""
    db = await open_db(database_path)
    try:
        await init_db(db)
    finally:
        await db.close()


def _create_http_session(settings: Settings) -> aiohttp.ClientSession:
    """Build a shared aiohttp session with reasonable global limits and timeouts."""
    timeout = aiohttp.ClientTimeout(
        total=settings.http_request_timeout_seconds,
        connect=settings.http_connect_timeout_seconds,
        sock_read=settings.http_request_timeout_seconds,
    )
    connector = aiohttp.TCPConnector(
        limit=settings.http_max_connections,
        limit_per_host=settings.http_max_connections,
        keepalive_timeout=settings.http_keepalive_timeout_seconds,
        enable_cleanup_closed=True,
    )
    return aiohttp.ClientSession(timeout=timeout, connector=connector)


async def startup_shared_resources(
    app: FastAPI,
    settings: Settings,
) -> tuple[aiohttp.ClientSession, AsyncIOScheduler]:
    """Create shared resources needed during the application lifespan.

    Args:
        app: The FastAPI application instance.
        settings: Resolved application settings.

    Returns:
        A tuple of ``(http_session, scheduler)``.
    """
    _check_single_worker_mode()

    db_path: Path = Path(settings.database_path)
    await run_blocking(db_path.parent.mkdir, parents=True, exist_ok=True)

    log.debug("database_directory_ensured", directory=str(db_path.parent))

    original_db_path = db_path.resolve()
    startup_db = await open_db(settings.database_path)
    try:
        await init_db(startup_db)
        setup_complete = await setup_service.is_setup_complete(startup_db)
        set_setup_complete_cache(app, setup_complete)
        log.debug("setup_completion_cached", completed=setup_complete)

        if setup_complete:
            runtime_database_path = await setup_service.get_runtime_database_path(startup_db)
            if runtime_database_path:
                if Path(runtime_database_path).resolve() != original_db_path:
                    await _ensure_database_schema(runtime_database_path)

                runtime_db = await open_db(runtime_database_path)
                try:
                    persisted_runtime_settings = (
                        await setup_service.get_persisted_runtime_settings(runtime_db)
                    )
                finally:
                    await runtime_db.close()

                if persisted_runtime_settings:
                    updated_settings = settings.model_copy(update=persisted_runtime_settings)
                    set_runtime_settings(app, updated_settings)
                    settings = updated_settings
                    log.info(
                        "runtime_settings_overridden_from_setup",
                        overrides=persisted_runtime_settings,
                    )

        # Create and initialize the GeoCache instance
        geo_cache = GeoCache()
        if Path(settings.database_path).resolve() != original_db_path:
            runtime_db = await open_db(settings.database_path)
            try:
                await geo_cache.load_cache_from_db(runtime_db)
                unresolved_count = await geo_cache.count_unresolved(runtime_db)
            finally:
                await runtime_db.close()
        else:
            await geo_cache.load_cache_from_db(startup_db)
            unresolved_count = await geo_cache.count_unresolved(startup_db)
    finally:
        await startup_db.close()

    await run_blocking(ensure_jail_configs, Path(settings.fail2ban_config_dir) / "jail.d")

    if unresolved_count > 0:
        log.warning("geo_cache_unresolved_ips", unresolved=unresolved_count)

    http_session: aiohttp.ClientSession = _create_http_session(settings)
    geo_cache.init_geoip(settings.geoip_db_path)
    app.state.geo_cache = geo_cache

    scheduler: AsyncIOScheduler | None = None
    try:
        scheduler = AsyncIOScheduler(timezone="UTC")
        scheduler.start()

        health_check.register(app)
        await blocklist_import.register(app)
        geo_cache_flush.register(app)
        geo_re_resolve.register(app)
        history_sync.register(app)

        return http_session, scheduler
    except Exception:
        with suppress(Exception):
            await http_session.close()
        if scheduler is not None:
            with suppress(Exception):
                scheduler.shutdown(wait=False)
        raise