import { useEffect, useRef, useState } from "react";

function fmt(ms: number): string {
  const total = Math.max(0, Math.floor(ms / 1000));
  return `${Math.floor(total / 60)}m ${total % 60}s`;
}

/**
 * Processing-time indicator: accumulates ONLY the time the harness/model is
 * actively working (`running`), pausing while a gate waits on the reviewer and
 * freezing when the session ends. The parent keys this component on the session id,
 * so it remounts (and restarts at zero) per session. In-memory: a page reload
 * restarts the count.
 */
export function ElapsedTimer({ running }: { running: boolean }) {
  const [accumMs, setAccumMs] = useState(0);
  const runStartRef = useRef<number | null>(null);
  const [, tick] = useState(0);

  useEffect(() => {
    if (!running) return;
    runStartRef.current = Date.now();
    const t = setInterval(() => tick((n) => n + 1), 1000);
    return () => {
      // Fold the just-finished run into the accumulator (setState re-renders so the
      // frozen total shows), then stop ticking.
      if (runStartRef.current != null) {
        const started = runStartRef.current;
        runStartRef.current = null;
        setAccumMs((ms) => ms + (Date.now() - started));
      }
      clearInterval(t);
    };
  }, [running]);

  const live = running && runStartRef.current != null ? Date.now() - runStartRef.current : 0;
  return (
    <span
      className="shrink-0 font-mono tabular-nums text-xs text-muted-foreground"
      aria-label="Processing time"
      title="Processing time (excludes time spent waiting on the reviewer)"
    >
      {fmt(accumMs + live)}
    </span>
  );
}