"""
core/debug_log.py

Tees stdout/stderr into an in-memory ring buffer + Qt signal so the Debug
window can show everything the app has printed since startup — including
messages from background poll threads (e.g. "[CMLLayer] poll error: ...") —
not just whatever gets printed while the window happens to be open.

install() should be called once, early, before anything prints. The real
streams are still written to, so running from a terminal is unaffected.
"""

from __future__ import annotations

import sys
from collections import deque
from typing import Optional

from PyQt6.QtCore import QObject, pyqtSignal


class _Broadcaster(QObject):
    line_written = pyqtSignal(str)


class _StreamTee:
    def __init__(self, real_stream, lines: deque, broadcaster: _Broadcaster):
        self._real        = real_stream
        self._lines       = lines
        self._broadcaster = broadcaster

    def write(self, text: str) -> None:
        self._real.write(text)
        if text:
            self._lines.append(text)
            self._broadcaster.line_written.emit(text)

    def flush(self) -> None:
        self._real.flush()

    def isatty(self) -> bool:
        return False


_lines:       Optional[deque]       = None
_broadcaster: Optional[_Broadcaster] = None


def install(max_lines: int = 2000) -> None:
    """Redirect sys.stdout/sys.stderr through the tee. Safe to call once."""
    global _lines, _broadcaster
    if _broadcaster is not None:
        return
    _lines       = deque(maxlen=max_lines)
    _broadcaster = _Broadcaster()
    sys.stdout   = _StreamTee(sys.stdout, _lines, _broadcaster)
    sys.stderr   = _StreamTee(sys.stderr, _lines, _broadcaster)


def get_broadcaster() -> Optional[_Broadcaster]:
    return _broadcaster


def get_history() -> str:
    return "".join(_lines) if _lines is not None else ""