// file: crates/ksp-logging-lib/tests/overhead.rs
// version: 2

//! Diagnostic gross-overhead probe for the reload layer used by KSP Logging.

use tracing_subscriber::layer::SubscriberExt; // rust-rules: trait-import

const ITERATIONS: u64 = 200_000;
const TEST_TARGET: &str = "ksp-logging-lib";

fn emit_probe_events() {
    for sequence in 0..ITERATIONS {
        tracing::trace!(target: TEST_TARGET, sequence, "reload overhead probe");
    }
}

fn trace_filter() -> tracing_subscriber::filter::Targets {
    return tracing_subscriber::filter::Targets::new()
        .with_default(tracing_subscriber::filter::LevelFilter::OFF)
        .with_target(TEST_TARGET, tracing_subscriber::filter::LevelFilter::TRACE);
}

#[test]
#[ignore = "diagnostic timing probe; run explicitly with --ignored --nocapture"]
fn reload_layer_overhead_remains_within_a_gross_regression_guardrail() {
    let baseline_subscriber = tracing_subscriber::registry().with(trace_filter());
    let baseline_start = std::time::Instant::now();
    tracing::subscriber::with_default(baseline_subscriber, || {
        emit_probe_events();
        return;
    });
    let baseline_elapsed = baseline_start.elapsed();
    let (reload_layer, _reload_handle) = tracing_subscriber::reload::Layer::new(trace_filter());
    let reload_subscriber = tracing_subscriber::registry().with(reload_layer);
    let reload_start = std::time::Instant::now();
    tracing::subscriber::with_default(reload_subscriber, || {
        emit_probe_events();
        return;
    });
    let reload_elapsed = reload_start.elapsed();
    let gross_ceiling = baseline_elapsed.saturating_mul(100).saturating_add(std::time::Duration::from_millis(100));
    println!("KSP reload overhead probe: baseline={baseline_elapsed:?}, reload={reload_elapsed:?}, iterations={ITERATIONS}");
    assert!(
        reload_elapsed <= gross_ceiling,
        "reload layer exceeded the gross regression guardrail: baseline={baseline_elapsed:?}, reload={reload_elapsed:?}"
    );
}