"""Read-only helpers for Steam's on-disk state (install/update progress).

Kept in its own leaf module (no intra-package imports) so both
``game_install`` and ``library_hider`` can use it without forming an import
cycle. ``STEAMAPPS_PATH`` lives here as the single source of truth for the
Steam library location.
"""

from __future__ import annotations

import os
from pathlib import Path
import re

STEAMAPPS_PATH = Path("~/.local/share/Steam/steamapps").expanduser()

# The real library path, captured before any test fixture redirects
# STEAMAPPS_PATH, so destructive helpers can refuse to touch it.
_REAL_STEAMAPPS = Path("~/.local/share/Steam/steamapps").expanduser()


def _assert_not_real_steam(path: Path) -> None:
    """Raise if *path* is inside the real Steam directory during tests.

    Defence-in-depth guard: when running under pytest, even if test
    fixtures fail to redirect ``STEAMAPPS_PATH``, destructive
    operations (uninstall, rmtree, unlink) will refuse to touch
    real files. In production runs this is a no-op.
    """
    if "PYTEST_CURRENT_TEST" not in os.environ:
        return  # production run — real Steam paths are expected
    try:
        path.resolve().relative_to(_REAL_STEAMAPPS.resolve())
    except ValueError:
        return  # path is NOT under real Steam — safe to proceed
    if STEAMAPPS_PATH.resolve() == _REAL_STEAMAPPS.resolve():
        msg = (
            f"SAFETY: refusing destructive operation on real Steam path "
            f"{path!s} — STEAMAPPS_PATH was not redirected by test fixtures"
        )
        raise RuntimeError(msg)


def steam_library_ready() -> bool:
    """Return True if Steam has an initialised library directory.

    When ``steamapps`` does not exist Steam has never completed first-run
    setup, so an install cannot succeed by any route: the ``steam://`` handler
    has nowhere to install to, and writing an appmanifest raises
    FileNotFoundError. Callers use this to skip provably-futile work rather
    than retrying it on every enforce pass.
    """
    return STEAMAPPS_PATH.is_dir()


def _manifest_transfer_active(manifest: Path) -> bool:
    """Return True if *manifest* shows unfinished download or staging bytes.

    Args:
        manifest: Path to an ``appmanifest_*.acf`` file.

    Returns:
        True if the app still has bytes left to download or stage to disk.
    """
    try:
        content = manifest.read_text(encoding="utf-8", errors="replace")
    except OSError:
        return False

    def _field(name: str) -> int:
        match = re.search(rf'"{name}"\s+"(\d+)"', content)
        return int(match.group(1)) if match else 0

    # BytesTo* are the totals for the in-flight update; BytesDownloaded/Staged
    # track progress. Progress strictly below the total means the update (or
    # its on-disk commit) is still running.
    return _field("BytesToDownload") > _field("BytesDownloaded") or _field(
        "BytesToStage"
    ) > _field("BytesStaged")


def steam_update_in_progress() -> bool:
    """Return True if any installed Steam app is mid-update.

    Steam records live transfer progress in each ``appmanifest_*.acf``: a game
    is actively updating while it still has bytes left to download or commit to
    disk. Restarting Steam during that window suspends the transfer and can
    leave a partially-written install — corrupting it. The enforcer checks this
    before bouncing Steam so it never interrupts an in-flight update (the
    failure that corrupted Age of Empires II DE into a deterministic launch
    crash).

    Returns:
        True if at least one appmanifest shows an unfinished download/stage.
    """
    try:
        manifests = list(STEAMAPPS_PATH.glob("appmanifest_*.acf"))
    except OSError:
        return False
    return any(_manifest_transfer_active(m) for m in manifests)


def is_game_fully_installed(app_id: int) -> bool:
    """Whether *app_id* is completely installed, not merely queued.

    :func:`_steam_client.is_game_installed` counts any manifest, which is right
    for "has an install been triggered". This is the stricter question a fast
    install needs: a manifest Steam wrote for its own slow download (no
    FullyInstalled bit, or bytes still in flight) is work to take over.

    Args:
        app_id: Steam application ID.

    Returns:
        True if the manifest has StateFlags bit 4 and no transfer in flight.
    """
    manifest = STEAMAPPS_PATH / f"appmanifest_{app_id}.acf"
    try:
        content = manifest.read_text(encoding="utf-8", errors="replace")
    except OSError:
        return False
    match = re.search(r'"StateFlags"\s+"(\d+)"', content)
    flags = int(match.group(1)) if match else 0
    return bool(flags & 4) and not _manifest_transfer_active(manifest)