"""Identify the host OS without losing the launcher's execution runtime."""

from __future__ import annotations

from dataclasses import dataclass
from pathlib import Path
import re


EXECUTION_OS_RELEASE = Path("/etc/os-release")
CONTAINER_HOST_OS_RELEASE = Path("/run/host/os-release")
STEAM_RUNTIME_OS_ID = "steamrt"


@dataclass(frozen=True)
class SystemIdentity:
	"""OS releases visible to the launcher process and its container host."""

	execution_release: dict[str, str]
	host_release: dict[str, str] | None

	@property
	def operating_system_release(self) -> dict[str, str]:
		return self.host_release or self.execution_release

	@property
	def running_inside_steam_runtime(self) -> bool:
		return (
			self.execution_release.get("ID", "").strip().casefold()
			== STEAM_RUNTIME_OS_ID
		)


def detect_system_identity(
	*,
	execution_os_release: Path = EXECUTION_OS_RELEASE,
	host_os_release: Path = CONTAINER_HOST_OS_RELEASE,
) -> SystemIdentity:
	"""Read the runtime OS and the standard container-host identity, if present."""

	execution = read_os_release(execution_os_release)
	host: dict[str, str] | None = None
	if execution.get("ID", "").strip().casefold() == STEAM_RUNTIME_OS_ID:
		candidate = read_os_release(host_os_release)
		candidate_id = candidate.get("ID", "").strip().casefold()
		if candidate_id and candidate_id != STEAM_RUNTIME_OS_ID:
			host = candidate
	return SystemIdentity(execution_release=execution, host_release=host)


def detect_distribution_id() -> str:
	"""Return the host distribution ID when a container exposes it."""

	release = detect_system_identity().operating_system_release
	return release.get("ID", "").strip().casefold()


def is_running_inside_steam_runtime() -> bool:
	"""Return whether the launcher process itself is inside Steam Runtime."""

	return detect_system_identity().running_inside_steam_runtime


def read_os_release(path: Path) -> dict[str, str]:
	"""Read bounded freedesktop os-release fields without invoking host tools."""

	try:
		lines = path.read_text(encoding="utf-8", errors="replace").splitlines()
	except OSError:
		return {}
	result: dict[str, str] = {}
	for line in lines:
		if not line or line.startswith("#") or "=" not in line:
			continue
		key, raw = line.split("=", 1)
		if not re.fullmatch(r"[A-Z][A-Z0-9_]*", key):
			continue
		value = raw.strip()
		if len(value) >= 2 and value[0] == value[-1] and value[0] in {"'", '"'}:
			value = value[1:-1]
		value = value.replace(r"\n", " ").replace(r"\"", '"').replace(r"\\", "\\")
		result[key] = value[:255]
	return result