//! Opt-in phase timings (`OXY_TIMINGS=1`): each named phase prints its
//! duration to stderr, for measuring where a command spends its time
//! without a profiler.

use std::sync::OnceLock;
use std::time::Instant;

fn enabled() -> bool {
    static ON: OnceLock<bool> = OnceLock::new();
    *ON.get_or_init(|| std::env::var_os("OXY_TIMINGS").is_some_and(|v| !v.is_empty() && v != "0"))
}

/// Report a duration measured by hand (several intervals summed), if timings are on.
pub fn record(name: &str, d: std::time::Duration) {
    if enabled() {
        eprintln!("timing {:<28} {:>9.2} ms", name, d.as_secs_f64() * 1000.0);
    }
}

/// Prints `timing <name> <ms>` when dropped, if timings are on.
pub struct Phase {
    name: &'static str,
    started: Option<Instant>,
}

/// Start timing a phase; the guard reports when it goes out of scope.
pub fn phase(name: &'static str) -> Phase {
    Phase {
        name,
        started: enabled().then(Instant::now),
    }
}

impl Drop for Phase {
    fn drop(&mut self) {
        if let Some(t) = self.started {
            eprintln!(
                "timing {:<28} {:>9.2} ms",
                self.name,
                t.elapsed().as_secs_f64() * 1000.0
            );
        }
    }
}