/**
 * 旧版单画布的自动保存Hook：短延迟备份本地草稿，较长延迟把最新快照交给CanvasSync。
 * 它使用旧快照writer，不是新版冻结请求ledger；本地recovery记录也不是可靠保存文件字节的资源仓库。
 */
"use client";
import { useEffect, useRef, useState } from "react";
import { api } from "@/lib/api";
import { canvasFingerprint, canvasPath, CanvasSync, type CanvasSnapshot, type SyncState } from "@/lib/canvas-sync";
import { decodeCanvas, type CanvasDocument } from "@/lib/canvas";

/** snapshot存在才建立远端writer，无snapshot仍可本地备份；writer在挂载时初始化一次，调用方应按画布重挂载。
 * key区分草稿作用域，paused阻断这里的新备份/入队，不在此取消已交给writer的请求。 */
export function useCanvasPersistence(document: CanvasDocument, workspace: string, board: string, key: string, snapshot: CanvasSnapshot | undefined, paused: boolean) {
  const [sync, setSync] = useState<SyncState>({ status: "saved", version: snapshot?.version || 1 });
  // alive限制writer通知更新已卸载组件；latest和pausedRef让异步回调读取当前文档/暂停值。
  const alive = useRef(false);
  const latest = useRef(document); latest.current = document;
  const pausedRef = useRef(paused); pausedRef.current = paused;
  // 同一挂载复用writer；状态变化时刷新sync并补本地备份，不随每次文档渲染新建同步器。
  const [writer] = useState(() => snapshot ? new CanvasSync(api, canvasPath(workspace, board), snapshot, (next) => {
    if (alive.current) { setSync(next); backup(); }
  }) : null);
  /** 保存规范化document、writer当前版本及内容指纹dirty；回调路径吞掉存储异常，定时effect路径会展示错误。 */
  function backup() {
    if (pausedRef.current) return;
    try {
      const current = latest.current;
      localStorage.setItem(key + ":recovery", JSON.stringify({ document: decodeCanvas(JSON.stringify(current)), baseVersion: writer?.version || 1, dirty: writer ? canvasFingerprint(current) !== writer.saved : false }));
    } catch { /* Storage failure is surfaced by the effect below. */ }
  }
  // 文档变化重置250ms本地/800ms远端计时器，形成防抖；暂停不建立计时器，清理只取消尚未触发的任务。
  useEffect(() => {
    if (paused) return;
    const local = setTimeout(() => {
      try { localStorage.setItem(key + ":recovery", JSON.stringify({ document: decodeCanvas(JSON.stringify(latest.current)), baseVersion: writer?.version || 1, dirty: writer ? canvasFingerprint(latest.current) !== writer.saved : false })); }
      catch { setSync({ status: "error", version: writer?.version || 1, error: "local_backup_failed" }); }
    }, 250);
    const remote = writer ? setTimeout(() => void writer.enqueue(latest.current), 800) : null;
    return () => { clearTimeout(local); if (remote) clearTimeout(remote); };
  }, [document, writer, key, paused]);
  // pagehide与卸载只执行同步本地backup，不保证远端请求在离页前完成；卸载后不再接收writer的UI通知。
  useEffect(() => {
    alive.current = true;
    /** 页面隐藏/离开时尽量保存当前内存文档，暂停状态由backup内部再次检查。 */
    const flush = () => backup();
    window.addEventListener("pagehide", flush);
    return () => { window.removeEventListener("pagehide", flush); backup(); alive.current = false; };
    // Writer and key are stable for this board's mounted editor.
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, [writer, key]);
  // retry先补本地备份再委托writer重试；没有远端writer时返回undefined，不伪造同步成功。
  return { ...sync, retry: () => { backup(); return writer?.retry(); } };
}