"""Speed acquisition and measured hold time; never infers motion from a command."""
from .protocol import SPEED_LIMITS


class SpeedHold:
    def __init__(self, erpm, duration, started):
        self.erpm, self.duration, self.started = erpm, duration, started
        self.previous = started
        self.tachometer = None
        self.motion_at = None
        self.stable_at = None
        self.hold_started = None
        self.lost_at = None
        self.rotation_s = 0.0
        self.phase = "accelerating"
        self.previous_good = False

    def update(self, now, value):
        delta = now - self.previous
        self.previous = now
        if self.tachometer is not None and value["tachometer"] != self.tachometer:
            self.motion_at = now
        self.tachometer = value["tachometer"]
        good = (abs(value["erpm"] - self.erpm) <= self.erpm * SPEED_LIMITS["speed_tolerance"]
                and self.motion_at is not None and now - self.motion_at <= 0.25)
        error = None
        if self.hold_started is None:
            if good:
                if self.stable_at is None: self.stable_at = now
                if now - self.stable_at >= SPEED_LIMITS["settle_s"]:
                    self.hold_started = now
                    self.phase = "holding"
            else:
                self.stable_at = None
            if self.hold_started is None and now - self.started >= SPEED_LIMITS["startup_timeout_s"]:
                error = "Мотор не вышел на заданную скорость за 15 секунд. Отсчёт вращения не начался."
        else:
            if good:
                # Both endpoints must be observed in band. Do not count a gap,
                # USB delay, stationary tachometer or an unobserved last interval.
                if self.previous_good and delta <= 0.25: self.rotation_s += delta
                self.lost_at = None
            else:
                if self.lost_at is None: self.lost_at = now
                if now - self.lost_at >= SPEED_LIMITS["lost_speed_timeout_s"]:
                    error = "Мотор перестал удерживать заданную скорость. Проверка завершена досрочно."
        self.previous_good = good
        if now - self.started > SPEED_LIMITS["startup_timeout_s"] + self.duration + 5:
            error = "Истёк общий срок проверки; заданное время вращения не набрано."
        done = self.rotation_s >= self.duration
        setpoint = min(self.erpm, max(1, (now - self.started) * SPEED_LIMITS["ramp_erpm_per_s"]))
        return setpoint, done, error