"""Command construction for the managed game window."""

from __future__ import annotations

import os
from pathlib import Path
import shutil
import sys
from typing import Mapping, Sequence

from .settings import Settings


MIN_GAME_CANVAS_DIMENSION = 320
MAX_GAME_CANVAS_DIMENSION = 16384
MAX_GAME_CONFIG_BYTES = 1024 * 1024


class GameboxConfigurationError(ValueError):
	"""Raised when stable outer scaling cannot use the game configuration."""


def find_gamescope(
	environment: Mapping[str, str] | None = None,
) -> str | None:
	"""Find Gamescope using the environment inherited by the game launch."""

	env = os.environ if environment is None else environment
	return shutil.which("gamescope", path=env.get("PATH"))


def read_game_canvas_size(game_config: Path) -> tuple[int, int]:
	"""Read the exact fixed render size advertised in ``game.ini``."""

	try:
		content = game_config.read_bytes()
	except OSError as exc:
		raise GameboxConfigurationError(
			f"could not read game window configuration {game_config}: {exc}"
		) from exc
	if len(content) > MAX_GAME_CONFIG_BYTES:
		raise GameboxConfigurationError(
			f"game window configuration is unexpectedly large: {game_config}"
		)
	if b"\x00" in content:
		raise GameboxConfigurationError(
			f"game window configuration uses an unsupported encoding: {game_config}"
		)
	try:
		text = content.decode("utf-8-sig")
	except UnicodeDecodeError as utf8_error:
		try:
			text = content.decode("cp1252")
		except UnicodeDecodeError:
			raise GameboxConfigurationError(
				f"game window configuration uses an unsupported encoding: {game_config}"
			) from utf8_error

	values: dict[str, int] = {}
	section: str | None = None
	for line_number, line in enumerate(text.splitlines(), start=1):
		stripped = line.strip()
		if stripped.startswith("[") and stripped.endswith("]"):
			section = stripped[1:-1].strip().casefold()
			continue
		if section != "screen" or not stripped or stripped.startswith((";", "#")):
			continue
		left, separator, right = line.partition("=")
		if not separator:
			continue
		key = left.strip().casefold()
		if key not in {"width", "height"}:
			continue
		if key in values:
			raise GameboxConfigurationError(
				f"duplicate [Screen] {key.title()} in {game_config}"
			)
		try:
			value = int(right.strip(), 10)
		except ValueError as exc:
			raise GameboxConfigurationError(
				f"invalid [Screen] {key.title()} on line {line_number} of {game_config}"
			) from exc
		if value < MIN_GAME_CANVAS_DIMENSION or value > MAX_GAME_CANVAS_DIMENSION:
			raise GameboxConfigurationError(
				f"[Screen] {key.title()} must be between "
				f"{MIN_GAME_CANVAS_DIMENSION} and {MAX_GAME_CANVAS_DIMENSION}"
			)
		values[key] = value
	if set(values) != {"width", "height"}:
		raise GameboxConfigurationError(
			f"game window configuration has no complete [Screen] Width/Height pair: "
			f"{game_config}"
		)
	return values["width"], values["height"]


def build_gamebox_command(
	game_command: Sequence[str],
	settings: Settings,
	*,
	game_size: tuple[int, int] | None = None,
	gamescope_path: str | None = None,
) -> list[str]:
	if not game_command:
		raise ValueError("game command cannot be empty")
	use_gamescope = (
		settings.allow_window_resizing
		and gamescope_path is not None
		and game_size is not None
	)
	command = [
		sys.executable,
		"-m",
		"ptlinux.gamebox_runtime",
		"--window-title",
		"PristonTale EU",
	]
	if settings.borderless:
		command.append("--borderless")
	if use_gamescope:
		command.append("--gamescope-scaling")
	if settings.suppress_unresponsive_warnings:
		command.append("--suppress-wm-ping")
	command.extend(("--", *[str(value) for value in game_command]))
	if not use_gamescope:
		return command

	assert gamescope_path is not None
	assert game_size is not None
	width, height = game_size
	if not (
		MIN_GAME_CANVAS_DIMENSION <= width <= MAX_GAME_CANVAS_DIMENSION
		and MIN_GAME_CANVAS_DIMENSION <= height <= MAX_GAME_CANVAS_DIMENSION
	):
		raise ValueError("game size is outside the supported Gamescope range")
	gamescope_command = [
		sys.executable,
		"-m",
		"ptlinux.gamescope_runtime",
		"--width",
		str(width),
		"--height",
		str(height),
		"--",
		gamescope_path,
		"-w",
		str(width),
		"-h",
		str(height),
		"-W",
		str(width),
		"-H",
		str(height),
		# Gamescope recalculates ``fit`` from each committed game buffer, so an
		# in-game resolution change keeps its own aspect ratio without cropping.
		"-S",
		"fit",
		"-F",
		"linear",
	]
	if settings.borderless:
		gamescope_command.append("--borderless")
	gamescope_command.extend(("--", *command))
	return gamescope_command