import time

class SystemClock:
    def __init__(self):
        self._update_time_ns = time.monotonic_ns()
        self._time = (0, 0, 0, 0)
        self._previous_timestamp = 0
        self._previous_utc_h = 0

    def update(self):
        self._update_time()
        current_timestamp = self.utc_timestamp
        if self._previous_utc_h == 23 and self.utc_time[0] == 0:
            current_timestamp += 86400
        delta = current_timestamp - self._previous_timestamp
        self._previous_timestamp = current_timestamp
        self._previous_utc_h = self.utc_time[0]
        return delta

    def _update_time(self):
        current_time = time.monotonic_ns()
        time_diff = current_time - self._update_time_ns
        self._update_time_ns = current_time
        s, ns = divmod(self._time[3]+time_diff, 1e9)
        m, s = divmod(self._time[2]+s, 60)
        h, m = divmod(self._time[1]+m, 60)
        _, h = divmod(self._time[0]+h, 24)
        self._time = (h, m, s, ns)

    def update_from_pps_clock(self, pps_time, pps_ref_monotonic):
        self._time = pps_time[:]
        self._update_time_ns = pps_ref_monotonic
        self._update_time()
        self._previous_timestamp = self.utc_timestamp

    @property
    def utc_time(self):
        self._update_time()
        return self._time

    @property
    def utc_timestamp(self):
        return self._time[0] * 3600 + self._time[1] * 60 + self._time[2] + (self._time[3] / 1_000_000_000)

    @property
    def update_time_ns(self):
        return self._update_time_ns