"""Application-level shared aiohttp.ClientSession.

All outgoing HTTP requests in the server package should use the shared
session returned by ``get_http_session()`` instead of creating
per-request ``aiohttp.ClientSession`` instances.  This keeps a single
TCP connection pool alive for the lifetime of the process, avoiding
the overhead of pool creation/teardown on every request.

Call ``close_http_session()`` once during application shutdown.
"""

from __future__ import annotations

import asyncio

import aiohttp

_DEFAULT_TIMEOUT = aiohttp.ClientTimeout(total=30, connect=10)

_session: aiohttp.ClientSession | None = None
_lock = asyncio.Lock()


async def get_http_session() -> aiohttp.ClientSession:
    """Get or create the shared HTTP session.

    Concurrent first-callers are serialized through ``_lock`` so we never
    leak a second ClientSession / connector pair. Once established, hot
    callers skip the lock via the fast-path check.
    """
    global _session
    if _session is not None and not _session.closed:
        return _session
    async with _lock:
        if _session is None or _session.closed:
            _session = aiohttp.ClientSession(timeout=_DEFAULT_TIMEOUT)
    return _session


async def close_http_session() -> None:
    """Close the shared HTTP session (call on app shutdown)."""
    global _session
    async with _lock:
        if _session is not None and not _session.closed:
            await _session.close()
        _session = None