ic-metrics 0.8.1

Allocation-free, dependency-free measurement arithmetic
Documentation 
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use crate::MeasurementAggregate;

use super::{MeasurementMeanError, MeasurementSummary};

#[test]
fn summary_mean_preserves_recording_and_saturation_contracts() {
    let mut summary = MeasurementSummary::EMPTY;
    assert_eq!(summary.mean(), Ok(None));
    summary.record(0);
    assert_eq!(summary.mean(), Ok(Some(0)));
    summary.record(9);
    assert_eq!(summary.mean(), Ok(Some(4)));
    summary.record(u64::MAX - 9);
    assert_eq!(summary.total(), u128::from(u64::MAX));
    assert_eq!(summary.mean(), Ok(Some(u128::from(u64::MAX) / 3)));
    assert!(!summary.aggregate().total_saturated());
    summary.record(1);
    assert_eq!(summary.mean(), Ok(Some((u128::from(u64::MAX) + 1) / 4)));
    assert!(!summary.aggregate().total_saturated());
    assert_eq!(summary.latest(), Some(1));
    let mut saturated_count = MeasurementSummary {
        aggregate: maximum_zero_count(),
        latest: 0,
    };
    assert_eq!(saturated_count.mean(), Ok(Some(0)));
    saturated_count.record(9);
    assert_eq!(
        saturated_count.mean(),
        Err(MeasurementMeanError::SaturatedSamples)
    );
}

#[test]
fn summary_means_are_available_in_constant_evaluation() {
    const PROJECTIONS: (Option<u128>, Option<u128>) = {
        let mut summary = MeasurementSummary::EMPTY;
        summary.record(9);
        summary.record(0);
        let Ok(mean) = summary.mean() else {
            panic!("exact mean")
        };
        let Ok(scaled) = summary.scaled_mean(10) else {
            panic!("exact scaled mean")
        };
        (mean, scaled)
    };
    assert_eq!(PROJECTIONS, (Some(4), Some(45)));
    let mut summary = MeasurementSummary::EMPTY;
    assert_eq!(summary.scaled_mean(10), Ok(None));
    summary.record(0);
    assert_eq!(summary.scaled_mean(10), Ok(Some(0)));
    summary = MeasurementSummary::from_parts(maximum_zero_count(), Some(0)).unwrap();
    assert_eq!(summary.scaled_mean(u64::MAX), Ok(Some(0)));
    summary.record(0);
    assert_eq!(
        summary.scaled_mean(0),
        Err(MeasurementMeanError::SaturatedSamples)
    );
}

#[test]
fn empty_and_measured_zero_are_distinct() {
    let mut summary = MeasurementSummary::EMPTY;
    assert_eq!(summary, MeasurementSummary::default());
    assert_eq!(summary.samples(), 0);
    assert_eq!(summary.total(), 0);
    assert_eq!(summary.latest(), None);
    assert_eq!(summary.maximum(), None);

    summary.record(0);
    assert_eq!(summary.samples(), 1);
    assert_eq!(summary.total(), 0);
    assert_eq!(summary.latest(), Some(0));
    assert_eq!(summary.maximum(), Some(0));
}

#[test]
fn latest_and_maximum_follow_individual_observations() {
    let mut summary = MeasurementSummary::EMPTY;
    for value in [7, 12, 3, 0] {
        summary.record(value);
    }
    assert_eq!(summary.samples(), 4);
    assert_eq!(summary.total(), 22);
    assert_eq!(summary.latest(), Some(0));
    assert_eq!(summary.maximum(), Some(12));
}

#[test]
fn total_saturation_preserves_count_latest_and_maximum() {
    let mut aggregate = MeasurementAggregate::EMPTY;
    for _ in 0..64 {
        aggregate.merge(aggregate);
        aggregate.record(u64::MAX);
    }
    aggregate.record(u64::MAX);
    aggregate.record(u64::MAX);
    let mut summary = MeasurementSummary {
        aggregate,
        latest: u64::MAX,
    };
    assert_eq!(summary.total(), u128::MAX);
    assert!(!summary.aggregate().total_saturated());
    summary.record(1);
    summary.record(2);
    assert_eq!(summary.samples(), u64::MAX);
    assert_eq!(summary.total(), u128::MAX);
    assert!(summary.aggregate().samples_saturated());
    assert!(summary.aggregate().total_saturated());
    assert_eq!(summary.latest(), Some(2));
    assert_eq!(summary.maximum(), Some(u64::MAX));
}

#[test]
fn count_saturation_does_not_freeze_other_observations() {
    let mut summary = MeasurementSummary {
        aggregate: maximum_zero_count(),
        latest: 0,
    };
    summary.record(4);
    assert_eq!(summary.samples(), u64::MAX);
    assert_eq!(summary.total(), 4);
    assert_eq!(summary.latest(), Some(4));
    assert_eq!(summary.maximum(), Some(4));
}

#[test]
fn recording_is_available_in_constant_evaluation() {
    const SUMMARY: MeasurementSummary = {
        let mut summary = MeasurementSummary::EMPTY;
        summary.record(9);
        summary.record(2);
        summary
    };
    assert_eq!(SUMMARY.samples(), 2);
    assert_eq!(SUMMARY.total(), 11);
    assert_eq!(SUMMARY.latest(), Some(2));
    assert_eq!(SUMMARY.maximum(), Some(9));
}

// Repeated disjoint zero-sample batches construct an exact cap without a fake
// production path or an impractically large recording loop.
fn maximum_zero_count() -> MeasurementAggregate {
    let mut aggregate = MeasurementAggregate::EMPTY;
    for _ in 0..64 {
        aggregate.merge(aggregate);
        aggregate.record(0);
    }
    aggregate
}