libretro/install.py

#!/usr/bin/env python3
"""Universal BIOS installer for retrogaming platforms.

Self-contained script using only Python stdlib. Downloads missing BIOS files
from the retrobios repository and places them in the correct location for
the detected emulator platform.

Usage:
    python install.py
    python install.py --platform retroarch --dest ~/custom/bios
    python install.py --check
    python install.py --list-platforms
"""
from __future__ import annotations

import argparse
import concurrent.futures
import hashlib
import json
import os
import platform
import re
import shutil
import sys
import tempfile
import threading
import urllib.error
import urllib.parse
import urllib.request
import xml.etree.ElementTree as ET
from pathlib import Path, PurePosixPath

# Manifests are read from the same ref the bootstrap verified this installer
# against, so a file list and the code reading it always come from one commit.
# RETROBIOS_REF pins an installation to a tag when reproducibility matters.
DEFAULT_RELEASE_REF = "main"
RELEASE_REF = os.environ.get("RETROBIOS_REF", DEFAULT_RELEASE_REF)
DEFAULT_BASE_URL = (
    "https://raw.githubusercontent.com/Abdess/retrobios/"
    + urllib.parse.quote(RELEASE_REF, safe="")
)


_LOOPBACK_HOSTS = ("localhost", "127.0.0.1", "::1")


def _checked_base_url(value: str) -> str:
    """Refuse a base URL that is neither HTTPS nor loopback.

    This base serves the manifest and the files it declares, so whoever
    controls it controls the expected hashes too and verification stops
    proving anything. install.sh and install.ps1 make the same check on the
    URL they fetch the installer from.

    Plain HTTP to loopback stays allowed: nothing sits between the two ends
    to intercept it, and it is how the installer is exercised end to end.
    """
    parsed = urllib.parse.urlparse(value)
    if parsed.scheme == "https":
        return value
    host = (parsed.hostname or "").lower()
    if parsed.scheme == "http" and host in _LOOPBACK_HOSTS:
        return value
    print(
        f"Error: RETROBIOS_BASE_URL must use HTTPS, got {value!r}",
        file=sys.stderr,
    )
    sys.exit(1)


BASE_URL = _checked_base_url(os.environ.get("RETROBIOS_BASE_URL", DEFAULT_BASE_URL))
MANIFEST_URL = f"{BASE_URL}/install/{{platform}}.json"
TARGETS_URL = f"{BASE_URL}/install/targets/{{platform}}.json"
RAW_FILE_URL = f"{BASE_URL}/{{path}}"
RELEASE_URL = (
    "https://github.com/Abdess/retrobios/releases/download/large-files/{asset}"
)
MAX_RETRIES = 3
MAX_MANIFEST_BYTES = 16 * 1024 * 1024
MAX_TARGETS_BYTES = 4 * 1024 * 1024
MAX_MANIFEST_FILES = 100_000
MAX_DOWNLOAD_SIZE = 1024 * 1024 * 1024
MAX_TOTAL_DOWNLOAD_SIZE = 64 * 1024 * 1024 * 1024
_SHA1_RE = re.compile(r"^[0-9a-fA-F]{40}$")
_SHA256_RE = re.compile(r"^[0-9a-fA-F]{64}$")

# Platforms with a manifest in install/. Manifest URLs are case sensitive,
# so user input is normalized against this list before any fetch.
AVAILABLE_PLATFORMS = (
    "retroarch", "batocera", "recalbox", "retrobat", "emudeck",
    "lakka", "retrodeck", "rocknix", "romm", "bizhawk", "misterfpga",
    "retropie",
)

# Fallback BIOS destination per platform when --platform is forced
# but auto-detection finds nothing on the machine.
DEFAULT_DESTS = {
    "batocera": Path("/userdata/bios"),
    "recalbox": Path("/recalbox/share/bios"),
    "lakka": Path("/storage/system"),
    "retrodeck": Path.home() / "retrodeck",
    "emudeck": Path.home() / "Emulation" / "bios",
    "rocknix": Path("/storage/roms/bios"),
    "misterfpga": Path("/media/fat/games"),
    "retropie": Path.home() / "RetroPie" / "BIOS",
    "romm": Path("/romm/library/bios"),
}


def _os_default_dests(os_type: str) -> dict[str, Path]:
    """Where a platform keeps its BIOS on this OS, when it is not detected.

    The same folders the platform's detection looks for: a platform named on
    the command line but not found must not land in ~/bios, which none of
    them reads.
    """
    home = Path.home()
    if os_type == "windows":
        profile = Path(os.environ.get("USERPROFILE", str(home)))
        appdata = Path(os.environ.get("APPDATA", str(home / "AppData" / "Roaming")))
        return {
            "retroarch": appdata / "RetroArch" / "system",
            # RetroBat's installer defaults to C:\RetroBat (installer.iss).
            "retrobat": Path("C:/RetroBat/bios"),
            "bizhawk": profile / "BizHawk" / "Firmware",
        }
    if os_type == "darwin":
        return {
            "retroarch": home / "Library" / "Application Support" / "RetroArch" / "system",
        }
    return {
        "retroarch": home / ".config" / "retroarch" / "system",
        "bizhawk": home / ".config" / "BizHawk" / "Firmware",
    }

# Set when the run is interrupted, so queued downloads end instead of draining
# the pool: every future is submitted before the first one completes.
_stop = threading.Event()

class _Interrupted(Exception):
    """Raised inside a worker once the run has been stopped."""


# The three RetroArch packages published for Android, newest ABI first.
ANDROID_RETROARCH_PACKAGES = (
    "com.retroarch.aarch64",
    "com.retroarch",
    "com.retroarch.ra32",
)


def _is_android() -> bool:
    """Android reports itself as Linux, so the runtime is named instead.

    Termux inherits the two variables the Android runtime exports, and
    /system/build.prop covers a shell that was started without them.
    """
    if os.environ.get("ANDROID_ROOT") and os.environ.get("ANDROID_DATA"):
        return True
    return Path("/system/build.prop").exists()


def detect_os() -> str:
    """Return normalized OS identifier.

    RETROBIOS_OS names the platform outright (linux, wsl, windows, darwin,
    android), for a run that has to behave like another host: the PowerShell
    wrapper tests drive a Windows layout on a Linux runner.
    """
    forced = os.environ.get("RETROBIOS_OS", "").strip().lower()
    if forced in ("linux", "wsl", "windows", "darwin", "android"):
        return forced
    system = platform.system().lower()
    if system == "linux":
        if _is_android():
            return "android"
        proc_version = Path("/proc/version")
        if proc_version.exists():
            try:
                content = proc_version.read_text(encoding="utf-8", errors="replace")
                if "microsoft" in content.lower():
                    return "wsl"
            except OSError:
                pass
        return "linux"
    if system == "darwin":
        return "darwin"
    if system == "windows":
        return "windows"
    return system


def _parse_os_release() -> dict[str, str]:
    """Parse /etc/os-release KEY=value format."""
    result: dict[str, str] = {}
    path = Path("/etc/os-release")
    if not path.exists():
        return result
    try:
        for line in path.read_text(encoding="utf-8", errors="replace").splitlines():
            line = line.strip()
            if "=" not in line or line.startswith("#"):
                continue
            key, _, value = line.partition("=")
            value = value.strip('"').strip("'")
            result[key] = value
    except OSError:
        pass
    return result


def _expand_retroarch_path(value: str, app_dir: Path) -> Path:
    """Expand the notations RetroArch writes into its config values.

    fill_pathname_expand_special (libretro-common/file/file_path.c) maps a
    leading '~' to the home directory and a leading ':' to the application
    directory, dropping the two leading characters in both cases.
    """
    if value[:1] == "~":
        return Path(str(Path.home())) / value[2:]
    if value[:1] == ":":
        return app_dir / value[2:]
    return Path(os.path.expandvars(os.path.expanduser(value)))


def _parse_retroarch_system_dir(
    cfg_path: Path, app_dir: Path | None = None
) -> Path | None:
    """Parse system_directory from retroarch.cfg.

    app_dir is RetroArch's application directory, used to expand ':' values.
    It defaults to the directory holding the config, which is where a portable
    install keeps both.
    """
    if not cfg_path.exists():
        return None
    app_dir = app_dir or cfg_path.parent
    try:
        for line in cfg_path.read_text(encoding="utf-8", errors="replace").splitlines():
            line = line.strip()
            if line.startswith("system_directory"):
                _, _, value = line.partition("=")
                value = value.strip().strip('"').strip("'")
                if not value or value == "default":
                    return app_dir / "system"
                return _expand_retroarch_path(value, app_dir)
    except OSError:
        pass
    return None


def _shell_unquote(value: str) -> str:
    """Resolve a shell right-hand side into its effective string value.

    Handles concatenated quoted/unquoted segments the way bash does
    (e.g. "/run/media/deck/EmuSD"/Emulation), expands variables in
    double-quoted and unquoted segments, and stops at unquoted
    whitespace or a comment.
    """
    parts: list[str] = []
    i = 0
    n = len(value)
    while i < n:
        c = value[i]
        if c == '"':
            end = value.find('"', i + 1)
            if end == -1:
                parts.append(os.path.expandvars(value[i + 1:]))
                break
            parts.append(os.path.expandvars(value[i + 1:end]))
            i = end + 1
        elif c == "'":
            end = value.find("'", i + 1)
            if end == -1:
                parts.append(value[i + 1:])
                break
            parts.append(value[i + 1:end])
            i = end + 1
        elif c.isspace() or c == "#":
            break
        else:
            end = i
            while end < n and value[end] not in "\"'#" and not value[end].isspace():
                end += 1
            parts.append(os.path.expandvars(value[i:end]))
            i = end
    return os.path.expanduser("".join(parts))


def _parse_bash_var(path: Path, key: str) -> str | None:
    """Extract the effective value of key= from a bash/shell file."""
    if not path.exists():
        return None
    try:
        for line in path.read_text(encoding="utf-8", errors="replace").splitlines():
            line = line.strip()
            if line.startswith(f"{key}="):
                _, _, value = line.partition("=")
                return _shell_unquote(value)
    except OSError:
        pass
    return None


def _parse_json_path(path: Path, *keys: str) -> str | None:
    """Extract a nested string value from a JSON file."""
    if not path.exists():
        return None
    try:
        data = json.loads(path.read_text(encoding="utf-8", errors="replace"))
        for key in keys:
            data = data[key]
        return data if isinstance(data, str) and data else None
    except (OSError, json.JSONDecodeError, KeyError, TypeError):
        return None


def _parse_ps1_var(path: Path, key: str) -> str | None:
    """Extract value of $key= or key= from a PowerShell file."""
    if not path.exists():
        return None
    normalized = key.lstrip("$")
    try:
        for line in path.read_text(encoding="utf-8", errors="replace").splitlines():
            line = line.strip()
            check = line.lstrip("$")
            if check.startswith(f"{normalized}="):
                _, _, value = check.partition("=")
                return value.strip('"').strip("'")
    except OSError:
        pass
    return None


def _detect_embedded() -> list[tuple[str, Path]]:
    """Check for embedded Linux retrogaming OSes."""
    found: list[tuple[str, Path]] = []
    os_release = _parse_os_release()
    os_id = os_release.get("ID", "").lower()

    if os_id == "rocknix":
        found.append(("rocknix", Path("/storage/roms/bios")))
        return found

    # MiSTer keeps the SD card at /media/fat with the main binary at its root
    # (Main_MiSTer file_io.cpp:1150-1156), and cores read from games/
    # (file_io.h:168)
    if Path("/media/fat/MiSTer").exists():
        found.append(("misterfpga", Path("/media/fat/games")))
        return found

    if Path("/etc/knulli-release").exists():
        found.append(("batocera", Path("/userdata/bios")))
        return found

    if os_id == "lakka":
        found.append(("lakka", Path("/storage/system")))
        return found

    if Path("/etc/batocera-version").exists():
        found.append(("batocera", Path("/userdata/bios")))
        return found

    if (
        Path("/recalbox/recalbox.version").exists()
        or Path("/usr/bin/recalbox-settings").exists()
    ):
        found.append(("recalbox", Path("/recalbox/share/bios")))
        return found

    if Path("/opt/muos").exists() or Path("/mnt/mmc/MUOS/").exists():
        found.append(("retroarch", Path("/mnt/mmc/MUOS/bios")))
        return found

    if Path("/home/ark").exists() and Path("/opt/system").exists():
        found.append(("retroarch", Path("/roms/bios")))
        return found

    if Path("/mnt/vendor/bin/dmenu.bin").exists():
        found.append(("retroarch", Path("/mnt/mmc/bios")))
        return found

    return found


def _android_storage_root() -> Path:
    """Shared storage root, the parent RetroArch builds its defaults from."""
    value = os.environ.get("EXTERNAL_STORAGE", "").strip()
    return Path(value) if value else Path("/storage/emulated/0")


def _detect_android() -> list[tuple[str, Path]]:
    """Find the RetroArch system directory on Android.

    The config is read from the app external files directory first, then from
    the internal one (platform_unix.c:1327-1395). A system_directory left at
    default resolves against <shared storage>/RetroArch, which is also where
    the directory sits when no config has been written yet
    (platform_unix.c:2836-2851).
    """
    found: list[tuple[str, Path]] = []
    storage = _android_storage_root()
    default_root = storage / "RetroArch"

    for package in ANDROID_RETROARCH_PACKAGES:
        for cfg in (
            storage / "Android" / "data" / package / "files" / "retroarch.cfg",
            Path("/data/data") / package / "files" / "retroarch.cfg",
        ):
            system_dir = _parse_retroarch_system_dir(cfg, default_root)
            if system_dir:
                found.append(("retroarch", system_dir))
                return found

    if default_root.exists():
        found.append(("retroarch", default_root / "system"))
    return found


def _lnk_target(lnk_path: Path, exe_name: str) -> Path | None:
    """Read the target path of a Windows shortcut.

    Shortcuts embed the target as a plain local path; scanning for it avoids
    parsing the whole .lnk structure for the one field that matters here.
    """
    try:
        if lnk_path.stat().st_size > 64 * 1024:
            return None
        blob = lnk_path.read_bytes()
    except OSError:
        return None
    pattern = re.compile(
        rb"[A-Za-z]:\\[ -~]{0,260}?" + re.escape(exe_name.encode()), re.IGNORECASE
    )
    match = pattern.search(blob)
    if not match:
        return None
    return Path(match.group().decode("ascii", "replace").replace("\\", "/"))


def launchbox_root(os_type: str) -> Path | None:
    """Locate the LaunchBox installation directory.

    LaunchBox installs wherever the user points its installer and writes no
    uninstall registry key, so the Start menu shortcut is the only record of
    that choice. Everything else falls back to the default location.
    """
    if os_type not in ("windows", "wsl"):
        return None
    candidates: list[Path] = []
    appdata = os.environ.get("APPDATA", "")
    if appdata:
        lnk = (
            Path(appdata)
            / "Microsoft"
            / "Windows"
            / "Start Menu"
            / "Programs"
            / "LaunchBox"
            / "LaunchBox.lnk"
        )
        if lnk.exists():
            target = _lnk_target(lnk, "LaunchBox.exe")
            if target:
                # The shortcut points at Core/LaunchBox.exe
                candidates.append(target.parent.parent)
                candidates.append(target.parent)
    userprofile = os.environ.get("USERPROFILE", "")
    if userprofile:
        candidates.append(Path(userprofile) / "LaunchBox")
    for root in candidates:
        if (root / "Data" / "Emulators.xml").exists():
            return root
    return None


def launchbox_emulators(emulators_xml: Path) -> dict[str, Path]:
    """Map each emulator LaunchBox knows about to its installation directory.

    LaunchBox stores its emulator list in Data/Emulators.xml; ApplicationPath
    is either absolute or relative to the LaunchBox root directory. Keys are
    the lowercase executable names.
    """
    found: dict[str, Path] = {}
    if not emulators_xml.exists():
        return found
    try:
        if emulators_xml.stat().st_size > 10 * 1024 * 1024:
            return found
        raw = emulators_xml.read_text(encoding="utf-8", errors="replace")
        # ElementTree expands internal entities; LaunchBox writes no doctype
        if "<!DOCTYPE" in raw.upper():
            return found
        tree = ET.ElementTree(ET.fromstring(raw))
    except (ET.ParseError, OSError):
        return found
    lb_root = emulators_xml.parent.parent
    for emu in tree.getroot().iter("Emulator"):
        app_path = (emu.findtext("ApplicationPath") or "").replace("\\", "/")
        if not app_path:
            continue
        exe = Path(app_path)
        if not exe.is_absolute():
            exe = lb_root / exe
        if exe.parent.is_dir():
            found.setdefault(exe.name.lower(), exe.parent)
    return found


def _launchbox_retroarch_system_dir(emulators_xml: Path) -> Path | None:
    """Resolve the system dir of a RetroArch referenced by LaunchBox.

    Mirrors the plugin's UpdateSystemPath: read system_directory from the
    retroarch.cfg sitting next to the executable, else assume system/.
    """
    emu_dir = launchbox_emulators(emulators_xml).get("retroarch.exe")
    if emu_dir is None:
        return None
    system_dir = _parse_retroarch_system_dir(emu_dir / "retroarch.cfg", emu_dir)
    return system_dir or emu_dir / "system"


def _pcsx2_bios_dir(emu_dir: Path) -> Path:
    """Resolve the BIOS folder of a PCSX2 installed under LaunchBox.

    EmuFolders (pcsx2/Pcsx2Config.cpp) enters portable mode when portable.ini
    or portable.txt sits next to the executable, and then takes the data root
    from the contents of portable.txt, relative to the executable. Otherwise
    the data root is Documents/PCSX2. Bios defaults to "bios" below it and the
    Bios key of PCSX2.ini overrides that.
    """
    documents = Path(os.environ.get("USERPROFILE", str(Path.home()))) / "Documents"
    portable_txt = emu_dir / "portable.txt"
    portable = (emu_dir / "portable.ini").exists() or portable_txt.exists()
    if portable:
        subpath = ""
        try:
            subpath = portable_txt.read_text(
                encoding="utf-8", errors="replace"
            ).strip()
        except OSError:
            pass
        data_root = emu_dir / subpath if subpath else emu_dir
    else:
        data_root = documents / "PCSX2"
    ini = data_root / "inis" / "PCSX2.ini"
    try:
        for line in ini.read_text(encoding="utf-8", errors="replace").splitlines():
            if line.startswith("Bios = "):
                value = line[len("Bios = "):].strip()
                candidate = Path(value)
                return candidate if candidate.is_absolute() else data_root / value
    except OSError:
        pass
    return data_root / "bios"


def _xemu_bios_dir(emu_dir: Path) -> Path:
    """Resolve the BIOS folder of a xemu managed by LaunchBox.

    Follows the plugin: xemu.toml next to the executable else the roaming
    copy, with bootrom_path and flashrom_path naming a file whose directory
    holds the images. Both default to bios/ under the executable.
    """
    appdata = os.environ.get("APPDATA", "")
    toml = emu_dir / "xemu.toml"
    if not toml.exists() and appdata:
        toml = Path(appdata) / "xemu" / "xemu" / "xemu.toml"
    if toml.exists():
        try:
            for line in toml.read_text(encoding="utf-8", errors="replace").splitlines():
                if line.startswith(("bootrom_path", "flashrom_path")):
                    parts = line.split("'")
                    if len(parts) > 1 and Path(parts[1]).exists():
                        return Path(parts[1]).parent
        except OSError:
            pass
    return emu_dir / "bios"


def launchbox_bios_dirs(root: Path) -> dict[str, Path]:
    """Map emulator ids to the BIOS directory LaunchBox expects for them.

    Only emulators whose destination LaunchBox itself computes are listed;
    the rest keep the default locations declared in the manifest.
    """
    emulators = launchbox_emulators(root / "Data" / "Emulators.xml")
    dirs: dict[str, Path] = {}
    emu_dir = emulators.get("pcsx2.exe")
    if emu_dir:
        dirs["pcsx2"] = _pcsx2_bios_dir(emu_dir)
    emu_dir = emulators.get("xemu.exe")
    if emu_dir:
        dirs["xemu"] = _xemu_bios_dir(emu_dir)
    emu_dir = emulators.get("dolphin.exe")
    if emu_dir and (emu_dir / "portable.txt").exists():
        # portable.txt beside the executable moves the user directory to
        # User (SetUserDirectory in Source/Core/UICommon/UICommon.cpp,
        # PORTABLE_USER_DIR in Source/Core/Common/CommonPaths.h)
        dirs["dolphin"] = emu_dir / "User"
    return dirs


def detect_frontends(os_type: str, home: Path | None = None) -> list[str]:
    """Detect frontends that reference emulators without owning a BIOS dir.

    ES-DE resolves its application data directory to $ESDE_APPDATA_DIR or
    <home>/ES-DE (es-core FileSystemUtil.cpp getAppDataDirectory).
    """
    home = home or Path.home()
    frontends: list[str] = []
    esde_env = os.environ.get("ESDE_APPDATA_DIR", "")
    if (esde_env and Path(esde_env).is_dir()) or (home / "ES-DE").is_dir():
        frontends.append("esde")
    if launchbox_root(os_type) is not None:
        frontends.append("launchbox")
    return frontends


def detect_platforms(os_type: str) -> list[tuple[str, Path]]:
    """Detect installed emulator platforms and their BIOS directories."""
    found: list[tuple[str, Path]] = []

    if os_type == "android":
        found.extend(_detect_android())

    if os_type in ("linux", "wsl"):
        found.extend(_detect_embedded())

        # EmuDeck (Linux/SteamOS)
        home = Path.home()
        emudeck_settings = home / ".config" / "EmuDeck" / "settings.sh"
        if emudeck_settings.exists():
            emu_path = _parse_bash_var(emudeck_settings, "emulationPath")
            if emu_path:
                bios_dir = Path(emu_path) / "bios"
                found.append(("emudeck", bios_dir))

        # RetroDECK: retrodeck.json since the cfg-to-json migration, which
        # renames the old retrodeck.cfg to retrodeck.bak (global.sh:149-153)
        retrodeck_conf_dir = home / ".var" / "app" / "net.retrodeck.retrodeck" / "config" / "retrodeck"
        retrodeck_json = retrodeck_conf_dir / "retrodeck.json"
        retrodeck_cfg = retrodeck_conf_dir / "retrodeck.cfg"
        if retrodeck_json.exists():
            rd_home = _parse_json_path(retrodeck_json, "paths", "rd_home_path")
            found.append(("retrodeck", Path(rd_home) if rd_home else home / "retrodeck"))
        elif retrodeck_cfg.exists():
            rd_home = _parse_bash_var(retrodeck_cfg, "rdhome")
            found.append(("retrodeck", Path(rd_home) if rd_home else home / "retrodeck"))

        # RetroArch Flatpak
        flatpak_cfg = home / ".var" / "app" / "org.libretro.RetroArch" / "config" / "retroarch" / "retroarch.cfg"
        ra_dir = _parse_retroarch_system_dir(flatpak_cfg)
        if ra_dir:
            found.append(("retroarch", ra_dir))

        # RetroArch Snap
        snap_cfg = home / "snap" / "retroarch" / "current" / ".config" / "retroarch" / "retroarch.cfg"
        ra_dir = _parse_retroarch_system_dir(snap_cfg)
        if ra_dir:
            found.append(("retroarch", ra_dir))

        # RetroArch native
        native_cfg = home / ".config" / "retroarch" / "retroarch.cfg"
        ra_dir = _parse_retroarch_system_dir(native_cfg)
        if ra_dir:
            found.append(("retroarch", ra_dir))

    if os_type == "darwin":
        home = Path.home()
        mac_cfg = home / "Library" / "Application Support" / "RetroArch" / "retroarch.cfg"
        ra_dir = _parse_retroarch_system_dir(mac_cfg)
        if ra_dir:
            found.append(("retroarch", ra_dir))

    if os_type in ("windows", "wsl"):
        # EmuDeck Windows
        home = Path.home()
        emudeck_ps1 = Path(os.environ.get("APPDATA", "")) / "EmuDeck" / "settings.ps1"
        if emudeck_ps1.exists():
            emu_path = _parse_ps1_var(emudeck_ps1, "$emulationPath")
            if emu_path:
                found.append(("emudeck", Path(emu_path) / "bios"))

        # RetroArch Windows
        appdata = os.environ.get("APPDATA", "")
        if appdata:
            win_cfg = Path(appdata) / "RetroArch" / "retroarch.cfg"
            ra_dir = _parse_retroarch_system_dir(win_cfg)
            if ra_dir:
                found.append(("retroarch", ra_dir))

        # RetroArch from Steam: a portable install under the default library
        for var in ("ProgramFiles(x86)", "ProgramFiles"):
            program_files = os.environ.get(var, "")
            if not program_files:
                continue
            steam_cfg = (
                Path(program_files) / "Steam" / "steamapps" / "common"
                / "RetroArch" / "retroarch.cfg"
            )
            ra_dir = _parse_retroarch_system_dir(steam_cfg)
            if ra_dir and not any(name == "retroarch" for name, _ in found):
                found.append(("retroarch", ra_dir))
                break

        # Portable RetroArch referenced by LaunchBox
        lb_root = launchbox_root(os_type)
        if lb_root and not any(name == "retroarch" for name, _ in found):
            system_dir = _launchbox_retroarch_system_dir(
                lb_root / "Data" / "Emulators.xml"
            )
            if system_dir:
                found.append(("retroarch", system_dir))

    return found


def normalize_platform(name: str) -> str:
    """Return the canonical platform id for user-supplied input."""
    plat = name.strip().lower()
    if plat not in AVAILABLE_PLATFORMS:
        print(f"Unknown platform '{name}'. Available platforms:", file=sys.stderr)
        for p in AVAILABLE_PLATFORMS:
            print(f"  {p}", file=sys.stderr)
        sys.exit(1)
    return plat


def _read_limited_json(response, limit: int, label: str) -> object:
    """Read a bounded UTF-8 JSON response."""
    raw_length = response.headers.get("Content-Length") if response.headers else None
    if raw_length:
        try:
            if int(raw_length) > limit:
                raise ValueError(f"{label} exceeds {limit} bytes")
        except ValueError as exc:
            if "exceeds" in str(exc):
                raise
    payload = response.read(limit + 1)
    if len(payload) > limit:
        raise ValueError(f"{label} exceeds {limit} bytes")
    try:
        return json.loads(payload.decode("utf-8"))
    except (UnicodeDecodeError, json.JSONDecodeError) as exc:
        raise ValueError(f"invalid {label}: {exc}") from exc


def _safe_relative_path(value: object, field: str) -> PurePosixPath:
    """Validate a manifest-controlled relative POSIX path."""
    if not isinstance(value, str) or not value or len(value) > 1024:
        raise ValueError(f"invalid {field}")
    if (
        "\\" in value
        or "\x00" in value
        or "//" in value
        or value.endswith("/")
        or re.match(r"^[A-Za-z]:", value)
    ):
        raise ValueError(f"unsafe {field}: {value!r}")
    path = PurePosixPath(value)
    if path.is_absolute() or any(part in ("", ".", "..") for part in path.parts):
        raise ValueError(f"unsafe {field}: {value!r}")
    return path


def _within(candidate: Path, root: Path) -> bool:
    """Whether *candidate* stays under *root* once both are resolved."""
    try:
        (root / candidate.name).resolve().relative_to(root)
    except (OSError, ValueError):
        return False
    return True


def _safe_target_dir(value: object, field: str) -> str:
    """Validate a manifest-controlled standalone-copy directory.

    These name emulator install directories, so unlike a BIOS destination they
    are legitimately absolute and outside the BIOS tree. What they must never
    do is climb: a '..' anywhere turns "copy next to the emulator" into "write
    wherever the manifest likes".
    """
    if not isinstance(value, str) or not value or len(value) > 2048:
        raise ValueError(f"invalid {field}")
    if "\x00" in value:
        raise ValueError(f"unsafe {field}: {value!r}")
    parts = re.split(r"[\\/]", value)
    if any(part == ".." for part in parts):
        raise ValueError(f"unsafe {field}: {value!r}")
    return value


def _destination_path(root: Path, value: object) -> Path:
    """Place a manifest destination below *root*.

    The manifest cannot climb: _safe_relative_path refuses absolute paths,
    drive letters and '..'. Symbolic links met under the root are the
    user's own layout and are followed. EmuDeck links bios/shadps4/sys_modules
    into shadPS4's data directory, and the file has to land where the
    emulator reads it.
    """
    relative = _safe_relative_path(value, "dest")
    return root.resolve() / Path(*relative.parts)


def _validate_manifest(data: object, plat: str) -> dict:
    """Validate the untrusted install-manifest boundary using stdlib only."""
    if not isinstance(data, dict):
        raise ValueError("manifest root must be an object")
    if data.get("manifest_version") not in (1, 2):
        raise ValueError("unsupported manifest_version")
    if data.get("platform") != plat:
        raise ValueError("manifest platform does not match request")
    files = data.get("files")
    if not isinstance(files, list) or len(files) > MAX_MANIFEST_FILES:
        raise ValueError("invalid manifest files list")

    seen_destinations: set[str] = set()
    total_size = 0
    for index, entry in enumerate(files):
        if not isinstance(entry, dict):
            raise ValueError(f"files[{index}] must be an object")
        dest = str(_safe_relative_path(entry.get("dest"), f"files[{index}].dest"))
        if dest in seen_destinations:
            raise ValueError(f"duplicate manifest destination: {dest}")
        seen_destinations.add(dest)

        size = entry.get("size")
        if isinstance(size, bool) or not isinstance(size, int) or not (0 <= size <= MAX_DOWNLOAD_SIZE):
            raise ValueError(f"invalid size for {dest}")
        total_size += size
        if total_size > MAX_TOTAL_DOWNLOAD_SIZE:
            raise ValueError("manifest total size exceeds safety limit")

        sha1 = entry.get("sha1", "")
        sha256 = entry.get("sha256", "")
        if sha1 and (not isinstance(sha1, str) or not _SHA1_RE.fullmatch(sha1)):
            raise ValueError(f"invalid SHA1 for {dest}")
        if sha256 and (
            not isinstance(sha256, str) or not _SHA256_RE.fullmatch(sha256)
        ):
            raise ValueError(f"invalid SHA256 for {dest}")
        if not sha1 and not sha256:
            raise ValueError(f"missing content hash for {dest}")

        release_asset = entry.get("release_asset")
        repo_path = entry.get("repo_path")
        if release_asset:
            asset = _safe_relative_path(release_asset, f"files[{index}].release_asset")
            if len(asset.parts) != 1:
                raise ValueError(f"release asset must be a basename: {release_asset}")
        elif repo_path:
            source = _safe_relative_path(repo_path, f"files[{index}].repo_path")
            if source.parts[0] != "bios":
                raise ValueError(f"repo_path outside bios/: {repo_path}")
        else:
            raise ValueError(f"no download source for {dest}")

        cores = entry.get("cores")
        if cores is not None and (
            not isinstance(cores, list) or not all(isinstance(core, str) for core in cores)
        ):
            raise ValueError(f"invalid cores list for {dest}")

    declared_total_files = data.get("total_files")
    if declared_total_files is not None and declared_total_files != len(files):
        raise ValueError("manifest total_files does not match files list")
    declared_total_size = data.get("total_size")
    if declared_total_size is not None and declared_total_size != total_size:
        raise ValueError("manifest total_size does not match file sizes")

    omitted = data.get("omitted_files", [])
    if not isinstance(omitted, list) or len(omitted) > MAX_MANIFEST_FILES:
        raise ValueError("invalid omitted_files list")
    seen_omitted: set[str] = set()
    allowed_omission_reasons = {
        "hash_mismatch", "not_found", "external", "user_provided"
    }
    for index, entry in enumerate(omitted):
        if not isinstance(entry, dict):
            raise ValueError(f"omitted_files[{index}] must be an object")
        dest = str(
            _safe_relative_path(
                entry.get("dest"), f"omitted_files[{index}].dest"
            )
        )
        if dest in seen_destinations or dest in seen_omitted:
            raise ValueError(f"duplicate or conflicting omitted destination: {dest}")
        seen_omitted.add(dest)
        if not isinstance(entry.get("name"), str) or not entry["name"]:
            raise ValueError(f"invalid omitted file name for {dest}")
        if not isinstance(entry.get("system", ""), str):
            raise ValueError(f"invalid omitted system for {dest}")
        if not isinstance(entry.get("required"), bool):
            raise ValueError(f"invalid omitted required flag for {dest}")
        if entry.get("reason") not in allowed_omission_reasons:
            raise ValueError(f"invalid omission reason for {dest}")
        cores = entry.get("cores")
        if cores is not None and (
            not isinstance(cores, list)
            or not all(isinstance(core, str) for core in cores)
        ):
            raise ValueError(f"invalid omitted cores list for {dest}")
    declared_total_omitted = data.get("total_omitted")
    if (
        declared_total_omitted is not None
        and declared_total_omitted != len(omitted)
    ):
        raise ValueError("manifest total_omitted does not match omitted_files")

    copies = data.get("standalone_copies", [])
    if not isinstance(copies, list) or len(copies) > 10_000:
        raise ValueError("invalid standalone_copies")
    for index, entry in enumerate(copies):
        if not isinstance(entry, dict):
            raise ValueError(f"standalone_copies[{index}] must be an object")
        if "file" in entry:
            _safe_relative_path(
                entry["file"], f"standalone_copies[{index}].file"
            )
        if "pattern" in entry:
            pattern = entry["pattern"]
            if (
                not isinstance(pattern, str)
                or not pattern
                or len(pattern) > 256
                or "/" in pattern
                or "\\" in pattern
                or ".." in pattern
            ):
                raise ValueError(f"invalid standalone copy pattern: {pattern!r}")
        targets = entry.get("targets", {})
        if targets and not isinstance(targets, dict):
            raise ValueError(f"invalid standalone copy targets at index {index}")
        for values in (targets or {}).values():
            if not isinstance(values, list) or len(values) > 100:
                raise ValueError(f"invalid standalone copy targets at index {index}")
            for value in values:
                _safe_target_dir(value, f"standalone_copies[{index}].targets")
    return data


def _validate_targets(data: object) -> dict[str, dict]:
    """Validate and normalize legacy list-valued target manifests.

    A null core list means the target publishes no core inventory. That is a
    known target with no filter, not a broken manifest: rejecting it would
    discard every other target on the platform.
    """
    if not isinstance(data, dict) or len(data) > 10_000:
        raise ValueError("invalid targets manifest")
    normalized: dict[str, dict] = {}
    for target, value in data.items():
        if not isinstance(target, str) or not target or len(target) > 128:
            raise ValueError("invalid target name")
        if isinstance(value, dict):
            cores = value.get("cores")
        else:
            cores = value
        if cores is None:
            normalized[target] = {"cores": None}
            continue
        if not isinstance(cores, list) or len(cores) > 10_000 or not all(
            isinstance(core, str) and 0 < len(core) <= 256 for core in cores
        ):
            raise ValueError(f"invalid core list for target {target}")
        normalized[target] = {"cores": cores}
    return normalized


def fetch_manifest(plat: str) -> dict:
    """Download platform manifest JSON."""
    url = MANIFEST_URL.format(platform=plat)
    try:
        with urllib.request.urlopen(url, timeout=30) as resp:
            return _validate_manifest(
                _read_limited_json(resp, MAX_MANIFEST_BYTES, "manifest"), plat
            )
    except (urllib.error.URLError, urllib.error.HTTPError, OSError, ValueError) as exc:
        print(f"  Failed to fetch manifest for {plat}: {exc}", file=sys.stderr)
        sys.exit(1)


def fetch_targets(plat: str) -> "dict | None":
    """Download the target core list.

    Empty on 404, where the platform publishes no targets. None when the list
    could not be read: a timeout says nothing about the platform, and
    answering "no targets" for it sent users to the full pack.
    """
    url = TARGETS_URL.format(platform=plat)
    try:
        with urllib.request.urlopen(url, timeout=30) as resp:
            return _validate_targets(
                _read_limited_json(resp, MAX_TARGETS_BYTES, "targets manifest")
            )
    except urllib.error.HTTPError as exc:
        if exc.code == 404:
            return {}
        print(f"  Error: failed to fetch targets for {plat}: {exc}", file=sys.stderr)
        return None
    except (urllib.error.URLError, OSError, ValueError) as exc:
        print(f"  Error: failed to fetch targets for {plat}: {exc}", file=sys.stderr)
        return None


def _filter_by_target(
    files: list[dict], target_cores: list[str]
) -> list[dict]:
    """Keep files where cores is None or overlaps with target_cores."""
    result: list[dict] = []
    target_set = set(target_cores)
    for f in files:
        cores = f.get("cores")
        if cores is None or any(c in target_set for c in cores):
            result.append(f)
    return result


def _digest_file(path: Path, algorithms: tuple[str, ...]) -> dict[str, str]:
    """Compute several digests of a file in a single read.

    Checking a 3 GB collection against both a SHA-1 and a SHA-256 used to walk
    every file twice, single threaded. Hashing is cheap next to the I/O, so
    the read is what has to happen once.
    """
    hashers = {name: hashlib.new(name) for name in algorithms}
    with open(path, "rb") as fh:
        for chunk in iter(lambda: fh.read(1024 * 1024), b""):
            for hasher in hashers.values():
                hasher.update(chunk)
    return {name: hasher.hexdigest() for name, hasher in hashers.items()}


def _sha1_file(path: Path) -> str:
    """Compute SHA1 of a file."""
    return _digest_file(path, ("sha1",))["sha1"]


def _sha256_file(path: Path) -> str:
    """Compute SHA256 of a file."""
    return _digest_file(path, ("sha256",))["sha256"]


def _classify_local(entry: dict, dest: Path) -> str:
    """Return 'up_to_date' or 'mismatched' for a file already on disk."""
    expected = {
        name: entry.get(name, "").lower()
        for name in ("sha256", "sha1")
        if entry.get(name)
    }
    if not expected:
        return "up_to_date"
    actual = _digest_file(dest, tuple(expected))
    if all(actual[name] == value for name, value in expected.items()):
        return "up_to_date"
    return "mismatched"


def check_local(
    files: list[dict], bios_path: Path, jobs: int = 8
) -> tuple[list[dict], list[dict], list[dict]]:
    """Check which files exist locally and have correct hashes.

    Returns (to_download, up_to_date, mismatched).
    """
    to_download: list[dict] = []
    present: list[tuple[dict, Path]] = []

    for f in files:
        dest = _destination_path(bios_path, f["dest"])
        if dest.exists():
            present.append((f, dest))
        else:
            to_download.append(f)

    up_to_date: list[dict] = []
    mismatched: list[dict] = []
    if present:
        with concurrent.futures.ThreadPoolExecutor(max_workers=jobs) as pool:
            verdicts = pool.map(
                lambda item: (item[0], _classify_local(item[0], item[1])), present
            )
            for entry, verdict in verdicts:
                if verdict == "up_to_date":
                    up_to_date.append(entry)
                else:
                    mismatched.append(entry)

    return to_download, up_to_date, mismatched


def _download_one(
    f: dict, bios_path: Path, verbose: bool = False
) -> tuple[str, bool]:
    """Download a single file. Returns (dest, success)."""
    if _stop.is_set():
        return str(f.get("dest", "?")), False
    try:
        dest = _destination_path(bios_path, f["dest"])
    except ValueError:
        return str(f.get("dest", "?")), False
    dest.parent.mkdir(parents=True, exist_ok=True)

    if f.get("release_asset"):
        url = RELEASE_URL.format(asset=urllib.parse.quote(f["release_asset"], safe=""))
    else:
        url = RAW_FILE_URL.format(path=urllib.parse.quote(f["repo_path"], safe="/"))

    for attempt in range(1, MAX_RETRIES + 1):
        tmp_path: Path | None = None
        try:
            with urllib.request.urlopen(url, timeout=60) as resp:
                expected_size = f["size"]
                raw_length = resp.headers.get("Content-Length") if resp.headers else None
                if raw_length and int(raw_length) != expected_size:
                    raise ValueError(
                        f"Content-Length {raw_length} != expected {expected_size}"
                    )
                with tempfile.NamedTemporaryFile(
                    mode="wb",
                    dir=dest.parent,
                    prefix=f".{dest.name}.",
                    suffix=".part",
                    delete=False,
                ) as out:
                    tmp_path = Path(out.name)
                    downloaded = 0
                    while True:
                        if _stop.is_set():
                            raise _Interrupted()
                        chunk = resp.read(1024 * 1024)
                        if not chunk:
                            break
                        downloaded += len(chunk)
                        if downloaded > expected_size or downloaded > MAX_DOWNLOAD_SIZE:
                            raise ValueError("download exceeded declared size")
                        out.write(chunk)
                if downloaded != expected_size:
                    raise ValueError(
                        f"downloaded {downloaded} bytes; expected {expected_size}"
                    )

            expected_sha256 = f.get("sha256", "")
            expected_sha1 = f.get("sha1", "")
            if expected_sha256 and _sha256_file(tmp_path) != expected_sha256.lower():
                if verbose:
                    print(f"    SHA256 mismatch on attempt {attempt}", file=sys.stderr)
                tmp_path.unlink(missing_ok=True)
                continue
            if expected_sha1:
                actual = _sha1_file(tmp_path)
                if actual != expected_sha1.lower():
                    if verbose:
                        print(f"    SHA1 mismatch on attempt {attempt}", file=sys.stderr)
                    tmp_path.unlink(missing_ok=True)
                    continue

            os.replace(tmp_path, dest)
            return f["dest"], True

        except _Interrupted:
            # Stopped mid-transfer: drop the scratch file rather than leaving
            # it beside the destination, and do not retry.
            if tmp_path is not None:
                tmp_path.unlink(missing_ok=True)
            return f["dest"], False

        except (
            urllib.error.URLError,
            urllib.error.HTTPError,
            OSError,
            ValueError,
        ) as exc:
            if verbose:
                print(f"    Attempt {attempt} failed: {exc}", file=sys.stderr)
            if tmp_path is not None:
                tmp_path.unlink(missing_ok=True)

    return f["dest"], False


def _locations(paths: list[Path]) -> str:
    """Where the run wrote, naming every destination when it served several."""
    return ", ".join(str(p) for p in paths) if paths else "nowhere"


def _plural(count: int, word: str) -> str:
    """Count and noun, so a run of one file does not read as machine output."""
    return f"{count} {word}" if count == 1 else f"{count} {word}s"


def _report_outcome(
    paths: list[Path],
    downloaded: int,
    up_to_date: int,
    errors: int,
    omitted: int,
    interrupted: bool,
) -> None:
    """Close the run on what happened, and leave with a status that says so.

    A run that installed nothing used to end on the word Done and a zero exit,
    which reads as success to a person and to a script alike.
    """
    if interrupted:
        print(f"\nStopped. {_plural(downloaded, 'file')} installed.")
        print("Run the same command again to carry on from here. Nothing is lost.")
        sys.exit(130)

    if errors and not downloaded:
        print(f"\nNothing was installed. {_plural(errors, 'file')} failed.")
        print(f"Location that was being written to: {_locations(paths)}")
        print("Run the same command again once that is resolved. "
              "Files already installed are kept.")
        sys.exit(2)

    if errors:
        print(f"\nFinished with errors. {_plural(downloaded, 'file')} installed, "
              f"{_plural(errors, 'file')} failed.")
        print(f"Location: {_locations(paths)}")
        print("Run the same command again to retry only those.")
        sys.exit(1)

    print(f"\nDone. {_plural(downloaded, 'file')} installed, "
          f"{_plural(up_to_date, 'file')} already up to date.")
    print(f"Location: {_locations(paths)}")
    if omitted:
        print(f"{_plural(omitted, 'file')} are not in the collection yet "
              "and were skipped.")
    print("To check this later, run the same command with --check.")


def _check_free_space(bios_path: Path, needed: int) -> None:
    """Stop before writing when the volume cannot hold the download.

    Reported against the nearest existing ancestor, since the destination
    itself may have just been created on a volume that is already full.
    """
    probe = bios_path
    while not probe.exists() and probe != probe.parent:
        probe = probe.parent
    try:
        free = shutil.disk_usage(probe).free
    except OSError:
        return
    if free >= needed:
        return
    print(f"\nNot enough space on the drive holding {bios_path}.", file=sys.stderr)
    print(f"  Needed: {format_size(needed)}. Free: {format_size(free)}.",
          file=sys.stderr)
    print(f"  Free up {format_size(needed - free)}, or use --dest to install "
          "to another drive.", file=sys.stderr)
    sys.exit(1)


def download_files(
    files: list[dict], bios_path: Path, jobs: int = 8, verbose: bool = False
) -> tuple[list[str], bool]:
    """Download files in parallel.

    Returns the destinations that failed and whether the run was interrupted.
    Every future is submitted up front, so a bare KeyboardInterrupt would let
    the pool drain the queue in full: the stop flag is what makes Ctrl+C end
    the run rather than only stop the reporting.
    """
    failed: list[str] = []
    total = len(files)
    interrupted = False
    _stop.clear()

    with concurrent.futures.ThreadPoolExecutor(max_workers=jobs) as pool:
        future_map = {
            pool.submit(_download_one, f, bios_path, verbose): f
            for f in files
        }
        done_count = 0
        try:
            for future in concurrent.futures.as_completed(future_map):
                done_count += 1
                dest, success = future.result()
                status = "ok" if success else "FAILED"
                print(f"  [{done_count}/{total}] {dest} {status}")
                if not success:
                    failed.append(dest)
        except KeyboardInterrupt:
            interrupted = True
            _stop.set()
            print("\n  Stopping. Files already installed are kept.")

    return failed, interrupted


def do_standalone_copies(
    manifest: dict, bios_path: Path, os_type: str,
    extra_dirs: dict[str, Path] | None = None,
) -> tuple[int, int, int]:
    """Copy BIOS files to standalone emulator directories.

    Supports:
    - file: single file copy
    - pattern: glob match (e.g. "scph*.bin")
    - note: informational message when detect path exists
    - WSL fallback to linux targets

    extra_dirs maps the emulator id of an entry to a root that replaces the
    default per-OS locations, for setups such as LaunchBox that keep their
    emulators outside them. The layout below the root is the same.

    Returns (copied, skipped, failed): skipped is a target directory that
    does not exist, failed a copy the system refused (permission, disk
    full, read-only mount), which used to be counted as "dir not found".
    """
    from fnmatch import fnmatch

    copies = manifest.get("standalone_copies", [])
    if not copies:
        return 0, 0, 0

    copied = 0
    skipped = 0
    failed = 0

    for entry in copies:
        # Note entries: print message if emulator detected
        if "note" in entry:
            detect_paths = entry.get("detect", {}).get(os_type, [])
            if not detect_paths and os_type == "wsl":
                detect_paths = entry.get("detect", {}).get("linux", [])
            for dp in detect_paths:
                expanded = Path(os.path.expandvars(os.path.expanduser(dp)))
                if expanded.is_dir():
                    print(f"  {entry['note']}")
                    break
            continue

        # Resolve source files
        if "pattern" in entry:
            sources = [
                f for f in bios_path.rglob("*")
                if fnmatch(f.name, entry["pattern"]) and f.is_file()
            ]
        else:
            src = bios_path / entry["file"]
            sources = [src] if src.exists() else []

        if not sources:
            continue

        # Resolve target directories with WSL fallback
        targets = entry.get("targets", {}).get(os_type, [])
        if not targets and os_type == "wsl":
            targets = entry.get("targets", {}).get("linux", [])

        target_dirs = [
            Path(os.path.expandvars(os.path.expanduser(t))) for t in targets
        ]
        extra_root = (extra_dirs or {}).get(entry.get("emulator", ""))
        if extra_root is not None:
            subdir = PurePosixPath(entry.get("file", "")).parent
            extra = extra_root if str(subdir) == "." else extra_root / subdir
            if extra not in target_dirs:
                target_dirs.append(extra)

        for target_dir in target_dirs:
            if not target_dir.is_dir():
                skipped += len(sources)
                continue
            resolved_dir = target_dir.resolve()
            for src in sources:
                dest = target_dir / src.name
                # A symlink already sitting at the destination would redirect
                # the write outside the directory the user opted into, and a
                # crafted source name would climb out of it.
                if dest.is_symlink() or not _within(dest, resolved_dir):
                    skipped += 1
                    continue
                try:
                    shutil.copy2(src, dest)
                    copied += 1
                except OSError as exc:
                    print(f"  ERROR: {dest}: {exc.strerror or exc}")
                    failed += 1

    return copied, skipped, failed


def format_size(n: int) -> str:
    """Human-readable file size."""
    if n < 1024:
        return f"{n} B"
    if n < 1024 * 1024:
        return f"{n / 1024:.1f} KB"
    if n < 1024 * 1024 * 1024:
        return f"{n / (1024 * 1024):.1f} MB"
    return f"{n / (1024 * 1024 * 1024):.1f} GB"


def _prompt_manual_platform(os_type: str) -> list[tuple[str, Path]]:
    """Ask for a platform and a BIOS directory when nothing was detected."""
    print("\nChoose the platform to install for:")
    for i, name in enumerate(AVAILABLE_PLATFORMS, 1):
        print(f"  {i}) {name}")
    print("  q) quit")
    print()
    plat = ""
    while not plat:
        try:
            choice = input("> ").strip().lower()
        except (EOFError, KeyboardInterrupt):
            print()
            sys.exit(0)
        if choice == "q":
            sys.exit(0)
        if choice.isdigit() and 1 <= int(choice) <= len(AVAILABLE_PLATFORMS):
            plat = AVAILABLE_PLATFORMS[int(choice) - 1]
        elif choice in AVAILABLE_PLATFORMS:
            plat = choice
    default_dest = _default_dest(os_type, plat)
    try:
        raw = input(f"BIOS directory [{default_dest}]: ").strip()
    except (EOFError, KeyboardInterrupt):
        print()
        sys.exit(0)
    dest = Path(raw).expanduser() if raw else default_dest
    if os_type == "windows" and raw:
        dest = Path(os.path.expandvars(raw))
    return [(plat, dest)]


def _default_dest(os_type: str, platform_name: str) -> Path:
    """Fall back path for a platform named on the command line but not found.

    A home directory is meaningless for RetroArch on Android, where Termux
    owns the home and the frontend reads from shared storage.
    """
    if os_type == "android" and platform_name == "retroarch":
        return _android_storage_root() / "RetroArch" / "system"
    return _os_default_dests(os_type).get(
        platform_name, DEFAULT_DESTS.get(platform_name, Path.home() / "bios")
    )


def _manual_usage_hint(os_type: str) -> list[str]:
    """How to name the platform and directory when nothing is detected."""
    if os_type == "windows":
        return [
            "  Use --platform and --dest to specify manually, for example:",
            "    & ([ScriptBlock]::Create((iwr -useb "
            "https://raw.githubusercontent.com/Abdess/retrobios/main/install.ps1))) "
            "--platform retroarch --dest 'C:\\RetroArch\\system'",
        ]
    if os_type == "android":
        return [
            "  Use --platform and --dest to specify manually, for example:",
            "    python3 install.py --platform retroarch "
            "--dest /storage/emulated/0/RetroArch/system",
        ]
    return [
        "  Use --platform and --dest to specify manually, for example:",
        "    python3 install.py --platform retroarch --dest ~/.config/retroarch/system",
    ]


def _prompt_platform_choice(
    platforms: list[tuple[str, Path]],
) -> list[tuple[str, Path]]:
    """Prompt user to choose among detected platforms."""
    print("\nInstall for:")
    for i, (name, path) in enumerate(platforms, 1):
        print(f"  {i}) {name.capitalize()} ({path})")
    if len(platforms) > 1:
        print(f"  {len(platforms) + 1}) All")
    print()

    while True:
        try:
            choice = input("> ").strip()
        except (EOFError, KeyboardInterrupt):
            print()
            sys.exit(0)
        if not choice:
            continue
        try:
            idx = int(choice)
        except ValueError:
            continue
        if 1 <= idx <= len(platforms):
            return [platforms[idx - 1]]
        if idx == len(platforms) + 1 and len(platforms) > 1:
            return platforms


def main() -> None:
    """Entry point."""
    parser = argparse.ArgumentParser(
        description="Download missing BIOS files for retrogaming emulators.",
    )
    parser.add_argument(
        "--platform",
        help="target platform (retroarch, batocera, emudeck, ...)",
    )
    parser.add_argument(
        "--dest",
        type=Path,
        help="override BIOS destination directory",
    )
    parser.add_argument(
        "--target",
        help="hardware target for core filtering (switch, rpi4, ...)",
    )
    parser.add_argument(
        "--check",
        action="store_true",
        help="check existing files without downloading",
    )
    parser.add_argument(
        "--list-platforms",
        action="store_true",
        help="list detected platforms and exit",
    )
    parser.add_argument(
        "--list-targets",
        action="store_true",
        help="list available targets for a platform and exit",
    )
    parser.add_argument(
        "--jobs", "-j",
        type=int,
        default=8,
        help="parallel download threads (default: 8)",
    )
    parser.add_argument(
        "--verbose", "-v",
        action="store_true",
        help="verbose output",
    )
    parser.add_argument(
        "--standalone-copies",
        action="store_true",
        help="opt in to copies into detected standalone-emulator directories",
    )

    args = parser.parse_args()
    if not 1 <= args.jobs <= 32:
        parser.error("--jobs must be between 1 and 32")
    print("RetroBIOS\n")

    os_type = detect_os()

    # Early exit for listing
    if args.list_platforms:
        print("Available platforms:")
        for p in AVAILABLE_PLATFORMS:
            print(f"  {p}")
        detected = detect_platforms(os_type)
        if detected:
            print("\nDetected on this system:")
            for name, path in detected:
                print(f"  {name}: {path}")
        return

    # Platform detection or override
    if args.platform:
        args.platform = normalize_platform(args.platform)
    if args.platform and args.dest:
        platforms = [(args.platform, args.dest)]
    elif args.platform:
        print("Detecting platform...")
        detected = detect_platforms(os_type)
        matched = [(n, p) for n, p in detected if n == args.platform]
        if matched:
            platforms = matched
        else:
            default_dest = _default_dest(os_type, args.platform)
            print(
                f"  Platform '{args.platform}' not detected, "
                f"using default path: {default_dest}"
            )
            platforms = [(args.platform, default_dest)]
    elif args.dest:
        print(f"  Using destination: {args.dest}")
        platforms = [("retroarch", args.dest)]
    else:
        print("Detecting platform...")
        frontends = detect_frontends(os_type)
        if "esde" in frontends:
            print("  Found ES-DE (BIOS files go to each emulator, not to ES-DE itself)")
        if "launchbox" in frontends:
            print("  Found LaunchBox")
        platforms = detect_platforms(os_type)
        if not platforms:
            print("  No supported platform detected.")
            if not sys.stdin.isatty() or args.list_targets:
                for line in _manual_usage_hint(os_type):
                    print(line)
                sys.exit(1)
            platforms = _prompt_manual_platform(os_type)
        for name, path in platforms:
            print(f"  Found {name.capitalize()} at {path}")

    if len(platforms) > 1 and not args.list_targets and sys.stdin.isatty():
        platforms = _prompt_platform_choice(platforms)

    total_downloaded = 0
    total_up_to_date = 0
    total_errors = 0
    total_omitted = 0
    total_interrupted = False
    installed_paths: list[Path] = []

    for plat_name, bios_path in platforms:
        if bios_path not in installed_paths:
            installed_paths.append(bios_path)
        print(f"\nFetching file index for {plat_name}...")
        manifest = fetch_manifest(plat_name)
        files = manifest.get("files", [])
        omitted_files = manifest.get("omitted_files", [])

        if args.list_targets:
            targets = fetch_targets(plat_name)
            if targets is None:
                sys.exit(1)
            if not targets:
                print(f"  No targets available for {plat_name}")
            else:
                for t in sorted(targets.keys()):
                    cores = targets[t].get("cores")
                    label = "no core list" if cores is None else f"{len(cores)} cores"
                    print(f"  {t} ({label})")
            continue

        # Target filtering
        if args.target:
            targets = fetch_targets(plat_name)
            if targets is None:
                sys.exit(1)
            target_info = targets.get(args.target)
            if target_info is None:
                # Carrying on would install every file, which is the opposite
                # of what a filter was asked for: a 4 GB download instead of
                # the subset the target needs. Refuse rather than ignore.
                print(
                    f"Error: unknown target '{args.target}' for {plat_name}.",
                    file=sys.stderr,
                )
                if targets:
                    print(
                        f"  available: {', '.join(sorted(targets))}", file=sys.stderr
                    )
                else:
                    print(
                        f"  {plat_name} publishes no target list", file=sys.stderr
                    )
                sys.exit(1)
            elif target_info.get("cores") is None:
                print(
                    f"  Target '{args.target}' publishes no core list; "
                    "installing every file"
                )
            else:
                target_cores = target_info["cores"]
                before = len(files)
                files = _filter_by_target(files, target_cores)
                omitted_files = _filter_by_target(omitted_files, target_cores)
                print(f"  Filtered {before} -> {len(files)} files for target {args.target}")

        total_size = sum(f.get("size", 0) for f in files)
        print(f"  {len(files)} files ({format_size(total_size)})")
        if omitted_files:
            required_omitted = sum(
                1 for entry in omitted_files if entry.get("required", True)
            )
            reasons: dict[str, int] = {}
            for entry in omitted_files:
                reason = entry.get("reason", "unknown")
                reasons[reason] = reasons.get(reason, 0) + 1
            reason_summary = ", ".join(
                f"{reason.replace('_', ' ')}: {count}"
                for reason, count in sorted(reasons.items())
            )
            print(
                f"  Safety notice: {len(omitted_files)} unavailable or unsafe "
                f"entries omitted ({required_omitted} required; {reason_summary})."
            )
            total_omitted += len(omitted_files)

        print("\nChecking existing files...")
        to_download, up_to_date, mismatched = check_local(
            files, bios_path, jobs=args.jobs
        )
        present = len(up_to_date) + len(mismatched)
        print(
            f"  {present}/{len(files)} present "
            f"({len(up_to_date)} verified, {len(mismatched)} wrong hash)"
        )

        # Mismatched files need re-download
        to_download.extend(mismatched)

        if args.check:
            if to_download:
                print(f"\n  {len(to_download)} files need downloading.")
            else:
                print("\n  All files up to date.")
            continue

        if to_download:
            dl_size = sum(f.get("size", 0) for f in to_download)
            print(f"\nDownloading {len(to_download)} files ({format_size(dl_size)})...")
            print("  Press Ctrl+C to stop. Running the same command again "
                  "carries on from here.")
            try:
                bios_path.mkdir(parents=True, exist_ok=True)
            except OSError as exc:
                print(f"\nCannot create {bios_path}.", file=sys.stderr)
                print(f"  {exc.strerror}.", file=sys.stderr)
                print("  On Batocera, Recalbox and ROCKNIX the BIOS folder "
                      "belongs to root: run the same command with sudo.",
                      file=sys.stderr)
                sys.exit(1)
            _check_free_space(bios_path, dl_size)
            failed, interrupted = download_files(
                to_download, bios_path, jobs=args.jobs, verbose=args.verbose
            )
            total_downloaded += len(to_download) - len(failed)
            total_errors += len(failed)
            if interrupted:
                total_interrupted = True
                break
        else:
            print("\n  All files up to date.")

        total_up_to_date += len(up_to_date)

        # Standalone copies
        if (
            manifest.get("standalone_copies")
            and not args.check
            and args.standalone_copies
        ):
            print("\nStandalone emulators:")
            lb_root = launchbox_root(os_type)
            extra_dirs = launchbox_bios_dirs(lb_root) if lb_root else None
            copied, skipped, copy_failed = do_standalone_copies(
                manifest, bios_path, os_type, extra_dirs
            )
            if copied or skipped or copy_failed:
                print(
                    f"  {copied} copied, {skipped} skipped (dir not found), "
                    f"{copy_failed} failed"
                )
            total_errors += copy_failed
        elif manifest.get("standalone_copies") and not args.check:
            print(
                "\nStandalone copies skipped "
                "(use --standalone-copies to opt in)."
            )

    if not args.check and not args.list_targets:
        _report_outcome(
            installed_paths,
            total_downloaded,
            total_up_to_date,
            total_errors,
            total_omitted,
            total_interrupted,
        )


if __name__ == "__main__":
    main()