import glob

import psutil

from app.sample import Sample

_temp_path: str | None = None
_temp_checked = False


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 _find_temp_path() -> str | None:
    """Find the sysfs file reporting CPU temperature, in millidegrees.

    Prefers hwmon sensors named k10temp (AMD), coretemp (Intel), or
    cpu_thermal (ARM), taking the first temp*_input of the first matching
    hwmon; falls back to the acpitz thermal zone. The result is cached by
    temp() for the process lifetime.

    Returns:
        The sysfs file to read, or None if no suitable sensor exists.
    """
    for hwmon in sorted(glob.glob("/sys/class/hwmon/hwmon*")):
        name = (_read(f"{hwmon}/name") or "").lower()
        if name in ("k10temp", "coretemp", "cpu_thermal"):
            for t in sorted(glob.glob(f"{hwmon}/temp*_input")):
                return t
            return None
    for zone in sorted(glob.glob("/sys/class/thermal/thermal_zone*")):
        if (_read(f"{zone}/type") or "").lower() == "acpitz":
            return f"{zone}/temp"
    return None


def temp() -> float | None:
    """Read the CPU temperature in degrees Celsius.

    The sensor path is resolved once via _find_temp_path. Sysfs reports
    millidegrees; the value is converted and rounded to 0.1 °C.

    Returns:
        Temperature in °C, or None if no sensor or unreadable value.
    """
    global _temp_path, _temp_checked
    if not _temp_checked:
        _temp_checked = True
        _temp_path = _find_temp_path()
    if _temp_path is None:
        return None
    v = _read(_temp_path)
    if not v:
        return None
    try:
        n = float(v)
    except ValueError:
        return None
    return round(n / 1000.0, 1)


def prime() -> None:
    """Prime psutil's CPU percent counter so the next call has a real delta.

    psutil.cpu_percent(None) returns 0.0 on its first call; sampler_loop
    invokes this before the first sample for that reason.
    """
    _ = psutil.cpu_percent(None)


def core_count() -> int:
    """Number of logical CPU cores (at least 1)."""
    return psutil.cpu_count(logical=True) or 1


def fill(s: Sample) -> None:
    """Fill the cpu, cpu_temp, and load-average fields of a Sample.

    Args:
        s: sample to fill.
    """
    s.cpu = psutil.cpu_percent(None)
    s.cpu_temp = temp()
    l1, l5, l15 = psutil.getloadavg()
    s.load1 = l1
    s.load5 = l5
    s.load15 = l15