//! A seam metered on this process's own energy count, as one span around the
//! whole pass, against an oracle that shares no code with the meter.
//!
//! Three interceptors each burn a different amount of their thread's CPU time
//! in one `before_model` pass. Each step is sealed with its share of the
//! pass's reading by thread CPU time (`ModelBased`), the shares sum to the
//! chain's figure, and that figure is the process's own energy over the pass:
//! no more than an oracle's window around it, and most of it. The oracle takes
//! its thread off its core its own way before each read (sleeps until the
//! process's context-switch count moves), then reads `ri_energy_nj` into a raw
//! buffer at the SDK's offset.

#![cfg(target_os = "macos")]

use ed25519_dalek::SigningKey;
use jcp_energy::Meter;
use jcp_intercept::{verify, Chain, Interceptor, ModelRequest, Step};
use jcp_schema::Provenance;
use std::time::Duration;

/// Burn `cpu` of this thread's own CPU time.
fn burn(cpu: Duration) {
    let start = jcp_energy::thread_cpu_time().expect("the thread clock");
    let mut x = 1u64;
    while jcp_energy::thread_cpu_time().expect("the thread clock") - start < cpu {
        for _ in 0..10_000 {
            x = std::hint::black_box(x.wrapping_mul(6_364_136_223_846_793_005).wrapping_add(1));
        }
    }
}

struct Burner {
    name: &'static str,
    cpu: Duration,
}

impl Interceptor for Burner {
    fn name(&self) -> &str {
        self.name
    }
    fn before_model(&mut self, _req: &mut ModelRequest) -> Step {
        burn(self.cpu);
        Step::Continue
    }
}

/// This process's `ri_energy_nj` (`proc_pid_rusage`, `RUSAGE_INFO_V6`, the
/// u64 at byte 336), after this thread has left its core: sleep 1, 2, 4, 8 ms
/// until the process's context-switch count (`pti_csw` would do; the rusage
/// `ri_user_time` is not enough) has moved. `ru_nvcsw + ru_nivcsw` of this
/// process is read with `getrusage`.
fn oracle_nj() -> u64 {
    fn switches() -> i64 {
        // SAFETY: `ru` is a valid, writable `rusage`.
        let mut ru: libc::rusage = unsafe { std::mem::zeroed() };
        assert_eq!(unsafe { libc::getrusage(libc::RUSAGE_SELF, &mut ru) }, 0);
        ru.ru_nvcsw + ru.ru_nivcsw
    }
    let before = switches();
    for ms in [1, 2, 4, 8] {
        std::thread::sleep(Duration::from_millis(ms));
        if switches() > before {
            break;
        }
    }
    let mut buf = [0u64; 58];
    // SAFETY: `buf` is 464 writable bytes, the size of `rusage_info_v6`.
    let rc = unsafe { libc::proc_pid_rusage(libc::getpid(), 6, buf.as_mut_ptr() as *mut libc::rusage_info_t) };
    assert_eq!(rc, 0, "proc_pid_rusage");
    buf[336 / 8]
}

#[test]
fn a_pass_is_one_reading_divided_among_its_steps_by_cpu_time() {
    let meter = Meter::detect();
    assert_eq!(meter.provenance(), Provenance::HwShunt, "this host's meter does not read a counter: {:?}", meter.rung());
    let steward = SigningKey::from_bytes(&[7u8; 32]);
    let mut misses = 0;
    for round in 0..10 {
        let mut c = Chain::new(steward.clone(), "did:jcp:test-intercept-pass")
            .with_meter(Meter::detect())
            .with(Box::new(Burner { name: "one", cpu: Duration::from_millis(2) }))
            .with(Box::new(Burner { name: "two", cpu: Duration::from_millis(4) }))
            .with(Box::new(Burner { name: "four", cpu: Duration::from_millis(8) }));
        let before = oracle_nj();
        assert!(c.before_model(&mut ModelRequest::default()).proceeds());
        let oracle = oracle_nj() - before;

        let recs: Vec<_> =
            c.receipts().iter().map(|e| verify(e, c.steward(), &c.steward_pubkey()).expect("a sealed step verifies")).collect();
        assert_eq!(recs.iter().map(|r| r.interceptor.as_str()).collect::<Vec<_>>(), ["one", "two", "four"]);
        let figures: Vec<u64> = recs.iter().map(|r| r.energy_uj).collect();
        let sum: u64 = figures.iter().sum();
        eprintln!(
            "intercept pass: round {round}: steps {figures:?} µJ ({:?}), sum {sum} µJ, chain {} µJ, oracle window {:.0} µJ",
            recs.iter().map(|r| r.provenance.as_str()).collect::<Vec<_>>(),
            c.energy_uj(),
            oracle as f64 / 1e3
        );
        assert_eq!(sum, c.energy_uj(), "the steps' shares are not the chain's figure");
        if recs.iter().any(|r| r.provenance != "ModelBased") {
            // A pass whose ends could not be read is the estimate, divided as one.
            assert!(recs.iter().all(|r| r.provenance == "Estimator"), "{recs:?}");
            misses += 1;
            continue;
        }
        // The shares follow the steps' own CPU time: 2 : 4 : 8 ms.
        assert!(figures[0] < figures[1] && figures[1] < figures[2], "{figures:?}");
        // The pass is the process's own energy over it: within the oracle's
        // window, and most of it.
        assert!(sum * 1_000 <= oracle + 1_000, "the pass ({sum} µJ) exceeds the oracle's window ({oracle} nJ)");
        assert!(sum * 1_000 * 3 >= oracle * 2, "the pass ({sum} µJ) is under two thirds of the oracle's window ({oracle} nJ)");
    }
    assert!(misses <= 1, "{misses} of 10 passes could not be read");
}