"""In-memory live log bus.

A thread-safe ring buffer that any part of Lyra can publish to and the web
server streams to the browser over SSE. Deliberately process-local and
ephemeral — it's an activity feed, not durable logging.
"""
from __future__ import annotations

import threading
import time
from collections import deque

_LOCK = threading.Lock()
_EVENTS: deque[dict] = deque(maxlen=500)
_SEQ = 0


def log(level: str, msg: str, **fields) -> None:
    """Publish an event. `level` is info/debug/error/system; fields are extras."""
    global _SEQ
    with _LOCK:
        _SEQ += 1
        _EVENTS.append(
            {"seq": _SEQ, "ts": time.time(), "level": level, "msg": msg, "fields": fields}
        )


def since(seq: int) -> list[dict]:
    """All buffered events with seq greater than `seq` (for SSE catch-up/polling)."""
    with _LOCK:
        return [e for e in _EVENTS if e["seq"] > seq]