"""
Run log.

Python buffers stdout when it is not a terminal, so a background run that hung
produced a zero-byte log and there was no way to see how far it had got — the
only evidence left was a screenshot. Every run now tees to
`Logs\\run_<timestamp>.log`, flushed per line, so a stuck or killed run still
leaves a readable trail.
"""

import sys
from datetime import datetime

from .. import settings as cfg


class _Tee:
    def __init__(self, stream, handle):
        self._stream = stream
        self._handle = handle

    def write(self, text):
        try:
            self._stream.write(text)
            self._stream.flush()
        except Exception:
            pass
        try:
            self._handle.write(text)
            self._handle.flush()      # a killed run must still have its log
        except Exception:
            pass
        return len(text)

    def flush(self):
        for target in (self._stream, self._handle):
            try:
                target.flush()
            except Exception:
                pass

    def isatty(self):
        return getattr(self._stream, "isatty", lambda: False)()


def _force_utf8_console() -> None:
    """
    Make the console accept the characters this bot actually prints.

    Windows hands Python a cp1252 console, which cannot encode an em dash or an
    arrow — and nearly every log line here has one. The tee below swallows the
    resulting UnicodeEncodeError so a run never dies of it, which is right but
    means those lines were being **silently dropped from the console** while
    landing correctly in the log file. Watching a run and reading its log
    afterwards showed different things, which is a nasty way to debug.

    `errors="replace"` as well as the encoding: a console that still cannot
    represent a character should print a box, not raise.
    """
    for stream in (sys.__stdout__, sys.__stderr__):
        try:
            stream.reconfigure(encoding="utf-8", errors="replace")
        except Exception:
            pass                     # not a real console, or too old to care

def start() -> "object":
    """Begin teeing stdout/stderr. Returns the log path."""
    _force_utf8_console()
    cfg.LOGS.mkdir(parents=True, exist_ok=True)
    path = cfg.LOGS / f"run_{datetime.now():%Y%m%d_%H%M%S}.log"
    handle = open(path, "a", encoding="utf-8", buffering=1)
    handle.write(f"\n{'=' * 70}\n{datetime.now():%Y-%m-%d %H:%M:%S} — run start\n"
                 f"{'=' * 70}\n")
    sys.stdout = _Tee(sys.__stdout__, handle)
    sys.stderr = _Tee(sys.__stderr__, handle)
    return path