cloudiful-rate-limiter 0.1.0

Reusable async resource throttling with local and Valkey-backed backends.
Documentation 
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use crate::error::InvalidPolicyError;
use std::time::Duration;

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum RateLimitPolicy {
    MinInterval { interval: Duration },
    PerMinute { rpm: u32 },
}

impl RateLimitPolicy {
    pub fn min_interval(interval: Duration) -> Result<Self, InvalidPolicyError> {
        Self::MinInterval { interval }.validated()
    }

    pub fn per_minute(rpm: u32) -> Result<Self, InvalidPolicyError> {
        Self::PerMinute { rpm }.validated()
    }

    pub fn interval(&self) -> Result<Duration, InvalidPolicyError> {
        match self {
            Self::MinInterval { interval } => {
                if interval.is_zero() {
                    return Err(InvalidPolicyError::zero_interval());
                }
                Ok(*interval)
            }
            Self::PerMinute { rpm } => {
                if *rpm == 0 {
                    return Err(InvalidPolicyError::zero_rpm());
                }
                let nanos_per_minute: u128 = Duration::from_secs(60).as_nanos();
                let interval_nanos = nanos_per_minute / u128::from(*rpm);
                if interval_nanos == 0 {
                    return Err(InvalidPolicyError::interval_out_of_range());
                }
                let interval_nanos = u64::try_from(interval_nanos)
                    .map_err(|_| InvalidPolicyError::interval_out_of_range())?;
                Ok(Duration::from_nanos(interval_nanos))
            }
        }
    }

    pub fn validated(self) -> Result<Self, InvalidPolicyError> {
        self.interval()?;
        Ok(self)
    }
}

#[cfg(test)]
mod tests {
    use super::RateLimitPolicy;
    use crate::InvalidPolicyKind;
    use std::time::Duration;

    #[test]
    fn per_minute_converts_to_even_interval() {
        let interval = RateLimitPolicy::per_minute(120)
            .unwrap()
            .interval()
            .unwrap();
        assert_eq!(interval, Duration::from_millis(500));
    }

    #[test]
    fn zero_rpm_is_invalid() {
        let error = RateLimitPolicy::per_minute(0).unwrap_err();
        assert_eq!(error.kind(), InvalidPolicyKind::ZeroRatePerMinute);
    }

    #[test]
    fn zero_interval_is_invalid() {
        let error = RateLimitPolicy::min_interval(Duration::ZERO).unwrap_err();
        assert_eq!(error.kind(), InvalidPolicyKind::ZeroInterval);
    }
}