"""Progress UI for instance-sync operations.

Two implementations sharing the ``Progress`` protocol:

  - :class:`HeadlessProgress` — no window; prints to stdout/stderr. Used when
    ``--no-gui`` is set OR when Qt isn't available (the only graphical path
    is Qt; there is no tkinter fallback).
  - :class:`QtProgressWindow` (in :mod:`cloud_sync.ui_qt`) — Qt modal window
    with the Prism-dark Steam-style layout.

The factory :func:`make_progress` picks Qt → Headless. Qt requires
PySide6 or PyQt6 to be importable. Install via
``pip install 'cloud-sync[qt]'`` or directly
``pip install PySide6``.
"""

from __future__ import annotations

import sys
from typing import Callable, Protocol


class Progress(Protocol):
    """Interface for status + cancellation reporting during a sync run."""

    def set_status(self, msg: str) -> None: ...
    def is_cancelled(self) -> bool: ...
    def run_with(self, worker: Callable[[], int], title: str) -> int: ...


class HeadlessProgress:
    """No-op progress. Status messages go to stdout, errors to stderr."""

    def set_status(self, msg: str) -> None:
        print(f"instance-sync: {msg}", flush=True)

    def is_cancelled(self) -> bool:
        return False

    def run_with(self, worker: Callable[[], int], title: str) -> int:
        self.set_status(title)
        return worker()


def make_progress(headless: bool) -> Progress:
    """Return the best Progress impl for the runtime + flags.

    Order:
      1. Qt window (PySide6 or PyQt6) — preferred when available.
      2. HeadlessProgress — fallback when ``--no-gui`` is set or Qt is
         missing. Logs to stdout/stderr.
    """
    if headless:
        return HeadlessProgress()
    try:
        from .ui_qt import QtProgressWindow
        return QtProgressWindow()
    except ImportError:
        print(
            "instance-sync: Qt (PySide6/PyQt6) not installed; "
            "running headless. Install with: pip install PySide6",
            file=sys.stderr,
        )
        return HeadlessProgress()
    except Exception as e:  # noqa: BLE001
        print(
            f"instance-sync: Qt init failed ({e}); falling back to headless",
            file=sys.stderr,
        )
        return HeadlessProgress()