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//! A module providing the `ErrorCount` metric.

use crate::atomic::AtomicInt;
use crate::clear::Clear;
use crate::metric::{Counter, Metric};
use aspect::{Advice, Enter, OnResult};
use serde::Serialize;

/// A metric counting how many times an expression typed std `Result` as returned an `Err` variant.
///
/// This is a light-weight metric.
///
/// By default, `ErrorCount` uses a lock-free `u64` `Counter`, which makes sense in multithread scenarios. Non-threaded applications can gain performance by using a `std::cell:Cell<u64>` instead.
#[derive(Clone, Default, Debug, Serialize)]
pub struct ErrorCount<C: Counter = AtomicInt<u64>>(C);

impl<C: Counter, T, E> Metric<Result<T, E>> for ErrorCount<C> {}

impl<C: Counter> Enter for ErrorCount<C> {
    type E = ();
    fn enter(&self) {}
}

impl<C: Counter, T, E> OnResult<Result<T, E>> for ErrorCount<C> {
    fn on_result(&self, _: (), r: &Result<T, E>) -> Advice {
        if r.is_err() {
            self.0.incr();
        };
        Advice::Return
    }
}

impl<C: Counter> Clear for ErrorCount<C> {
    fn clear(&self) {
        self.0.clear()
    }
}