//! STG (stage-timestamp) instrumentation for the jank hunt, 2026-10-28.
//!
//! The app's FR hook (rendering notifier) measures render cost and frame
//! gaps; this measures what happens AROUND rendering inside the event
//! loop: Choreographer wake latency, timer callbacks (the app's 8 ms
//! drain tick runs in `update_timers_and_animations`), and event
//! processing. Timestamps are plain atomics — the UI thread only does
//! atomic loads/stores here; the APP formats the log line from its own
//! tick (never log from the UI thread: logd backpressure).

use std::sync::atomic::{AtomicU64, Ordering};
use std::time::Instant;

static T0: std::sync::OnceLock<Instant> = std::sync::OnceLock::new();
pub fn now_us() -> u64 {
    T0.get_or_init(Instant::now).elapsed().as_micros() as u64
}

// Per-iteration stage marks (us since process start); reset at loop top.
pub static S_START: AtomicU64 = AtomicU64::new(0);
pub static S_FIRST_EV: AtomicU64 = AtomicU64::new(0);
pub static S_POLL_END: AtomicU64 = AtomicU64::new(0);
pub static S_RENDER_START: AtomicU64 = AtomicU64::new(0);
pub static S_RENDER_END: AtomicU64 = AtomicU64::new(0);
// Accumulated per-iteration costs.
pub static S_TIMER_US: AtomicU64 = AtomicU64::new(0);
pub static S_EVENT_US: AtomicU64 = AtomicU64::new(0);
pub static S_N_EVENTS: AtomicU64 = AtomicU64::new(0);
// Full do_render duration of the PREVIOUS iteration (the AfterRendering
// hook fires mid-render, so the current iteration's render can't be read
// yet): covers renderer.draw PLUS the wgpu surface tail (flush_and_submit
// gr_context.submit + queue.present — the Mali driver calls).
pub static S_LAST_RENDER_US: AtomicU64 = AtomicU64::new(0);

/// One iteration of the event loop: start, first-event, poll-end,
/// render-start, render-end, timer-us, event-us, n-events.
pub fn snapshot() -> (u64, u64, u64, u64, u64, u64, u64, u64) {
    (
        S_START.load(Ordering::Relaxed),
        S_FIRST_EV.load(Ordering::Relaxed),
        S_POLL_END.load(Ordering::Relaxed),
        S_RENDER_START.load(Ordering::Relaxed),
        S_RENDER_END.load(Ordering::Relaxed),
        S_TIMER_US.load(Ordering::Relaxed),
        S_EVENT_US.load(Ordering::Relaxed),
        S_N_EVENTS.load(Ordering::Relaxed),
    )
}