import argparse
import os
import sys


# parse_args: function definition for ScanSlicer behavior.
def parse_args(argv=None):
    parser = argparse.ArgumentParser(
        prog="scanslicer",
        description="ScanSlicer Qt UI (Wayland/X11)",
    )
    parser.add_argument(
        "path",
        nargs="?",
        help="Optional input directory containing images",
    )
    parser.add_argument(
        "--backend",
        choices=("auto", "wayland", "x11"),
        default="auto",
        help="Display backend selection (default: auto)",
    )
    return parser.parse_args(argv)


# _detect_backend_from_qpa_env: function definition for ScanSlicer behavior.
def _detect_backend_from_qpa_env():
    qpa_value = os.environ.get("QT_QPA_PLATFORM", "").strip().lower()
    if not qpa_value:
        return None

    tokens = [token.strip() for token in qpa_value.split(";") if token.strip()]
    for token in tokens:
        if token == "wayland":
            return "wayland"
        if token in ("xcb", "x11"):
            return "x11"
    return None


# resolve_runtime_backend: function definition for ScanSlicer behavior.
def resolve_runtime_backend(backend):
    if backend in ("wayland", "x11"):
        return backend

    env_backend = _detect_backend_from_qpa_env()
    if env_backend is not None:
        return env_backend

    session_type = os.environ.get("XDG_SESSION_TYPE", "").strip().lower()
    if session_type == "wayland":
        return "wayland"
    if session_type == "x11":
        return "x11"

    runtime_dir = os.environ.get("XDG_RUNTIME_DIR", "").strip()
    wayland_display = os.environ.get("WAYLAND_DISPLAY", "").strip()
    if runtime_dir and wayland_display and os.path.exists(os.path.join(runtime_dir, wayland_display)):
        return "wayland"

    if os.environ.get("DISPLAY", "").strip():
        return "x11"

    # Fall back to Wayland when auto-detection has no clear signal.
    return "wayland"