from time import perf_counter_ns
from .types import IntOrNone


def ns_to_string(ns: int) -> str:
    units = ['ns', 'µs', 'ms', 's']
    unit = 0
    while ns > 1_000:
        ns /= 1_000
        unit += 1
        if unit == len(units) - 1:
            break

    return f"{ns:1.2f}{units[unit]}"


class StopWatch:
    started: IntOrNone = None
    stopped: IntOrNone = None

    def __init__(self, auto_start=True):
        if auto_start:
            self.start()

    def start(self):
        self.started = perf_counter_ns()
        self.stopped = None

    def stop(self) -> int:
        self.stopped = perf_counter_ns()
        return self.elapsed()

    reset = start

    def elapsed(self) -> int:
        if self.stopped is None:
            return perf_counter_ns() - self.started
        else:
            return self.stopped - self.started

    def avg_elapsed(self, divider: int) -> int:
        return self.elapsed() // divider  # in ns precision loosing some rounding error probably will not hurt

    def elapsed_string(self):
        return ns_to_string(self.elapsed())

    def avg_string(self, divider: int) -> str:
        return ns_to_string(self.avg_elapsed(divider))

    def __str__(self):
        return self.avg_string(1)