import { useEffect, useRef } from "react";
import { createLocalStats, type StatsStore } from "./readingStats";

const TICK = 30; // 秒：可见期间心跳粒度

/** Reader 页挂一次：可见期间每 30s 落一笔，隐藏/卸载即 flush。 */
export function useReadingSession(store: StatsStore = createLocalStats()) {
  const acc = useRef(0);
  const last = useRef(0);
  useEffect(() => {
    last.current = Date.now(); // 渲染期不取时钟，effect 内初始化起算点
    const flush = () => {
      const now = Date.now();
      if (document.visibilityState === "visible") acc.current += (now - last.current) / 1000;
      last.current = now;
      if (acc.current >= 1) {
        store.record(acc.current);
        acc.current = 0;
      }
    };
    const t = setInterval(flush, TICK * 1000);
    const onVis = () => flush();
    document.addEventListener("visibilitychange", onVis);
    globalThis.addEventListener?.("pagehide", onVis);
    return () => {
      clearInterval(t);
      document.removeEventListener("visibilitychange", onVis);
      globalThis.removeEventListener?.("pagehide", onVis);
      flush();
    };
  }, [store]);
}