import glob

from app.sample import Sample

_PS = "/sys/class/power_supply"


def _read(path: str) -> str | None:
    """Read a sysfs file, returning its stripped contents.

    Args:
        path: path under /sys.

    Returns:
        The file contents, or None if it cannot be read.
    """
    try:
        with open(path) as f:
            return f.read().strip()
    except OSError:
        return None


def _supplies() -> list[tuple[str, str]]:
    """List power supplies found under /sys/class/power_supply.

    Returns:
        (type, path) pairs sorted by path, where type is the sysfs type
        ("battery", "mains", "usb", ...) of each supply.
    """
    out: list[tuple[str, str]] = []
    for p in sorted(glob.glob(f"{_PS}/*")):
        t = _read(f"{p}/type")
        if t:
            out.append((t.lower(), p))
    return out


def fill(s: Sample) -> None:
    """Fill the battery / ac_online fields of a Sample from sysfs.

    psutil's battery API is unreliable here (power_plugged can be None),
    so /sys/class/power_supply/* is read directly: the first present
    battery provides capacity and status, and ac_online becomes True when
    any mains — or, failing that, USB — supply reports online. Fields stay
    at their Sample defaults on a desktop without these nodes.

    Args:
        s: sample to fill.
    """
    try:
        supplies = _supplies()
        for t, p in supplies:
            if t == "battery" and _read(f"{p}/present") == "1":
                cap = _read(f"{p}/capacity")
                if cap is not None:
                    try:
                        s.battery = int(cap)
                    except ValueError:
                        pass
                    s.battery_status = _read(f"{p}/status")
                break
        for t, p in supplies:
            if t == "mains" and _read(f"{p}/online") == "1":
                s.ac_online = True
                break
        if s.ac_online is None:
            for t, p in supplies:
                if t == "usb" and _read(f"{p}/online") == "1":
                    s.ac_online = True
                    break
    except OSError:
        pass