/**
 * Draft Save Worker
 *
 * 在 Web Worker 中执行草稿序列化和指纹计算，避免阻塞主线程。
 * 主线程通过 postMessage 传入 canvas 快照，Worker 返回序列化后的 payload。
 *
 * 放置在 public/ 下以从同源加载，避免 assetPrefix (CDN) 导致的跨域 Worker 加载失败。
 */

let lastFingerprint = "";

/** Canonical source: src/views/canvas/workers/draftSaveUtils.ts — keep in sync */
function djb2(str) {
  let hash = 5381;
  for (let i = 0; i < str.length; i++) {
    hash = ((hash << 5) + hash + str.charCodeAt(i)) | 0;
  }
  return hash >>> 0;
}

/**
 * 计算草稿指纹：O(n log n) 排序保证一致性
 */
function computeFingerprint(nodes, edges, viewport) {
  const nodeFingerprints = nodes
    .map(
      (n) =>
        `${n.id}:${n.position?.x ?? 0},${n.position?.y ?? 0}:${typeof n.data === "object" ? djb2(JSON.stringify(n.data)) : 0}`,
    )
    .sort()
    .join("|");
  const edgeFingerprints = edges
    .map((e) => `${e.id}:${e.source}-${e.target}`)
    .sort()
    .join("|");
  const vp = `V${Math.round(viewport.position.x)},${Math.round(viewport.position.y)},${viewport.zoom.toFixed(2)}`;
  return `N${nodes.length}E${edges.length}:${vp}:${nodeFingerprints}::${edgeFingerprints}`;
}

/**
 * 清理 blob:/data: URL，避免序列化无效引用
 */
function sanitizeDraftJson(draftJson) {
  try {
    const data = JSON.parse(draftJson);
    return JSON.stringify(data, (_key, value) => {
      if (
        typeof value === "string" &&
        (value.startsWith("blob:") || value.startsWith("data:"))
      ) {
        return "";
      }
      return value;
    });
  } catch {
    return draftJson;
  }
}

self.onmessage = (e) => {
  try {
    const { nodes, edges, viewport, projectUuid, syncVersion } = e.data;

    const fingerprint = computeFingerprint(nodes, edges, viewport);
    if (fingerprint === lastFingerprint) {
      self.postMessage({ type: "result", fingerprint, payload: null });
      return;
    }

    lastFingerprint = fingerprint;

    const draftData = {
      nodes,
      edges,
      savedAt: Date.now(),
      version: syncVersion,
    };
    const draftJson = sanitizeDraftJson(JSON.stringify(draftData));

    self.postMessage({
      type: "result",
      fingerprint,
      payload: {
        projectUuid,
        draftJson,
        viewportX: viewport.position.x.toString(),
        viewportY: viewport.position.y.toString(),
        viewportZoom: viewport.zoom.toString(),
      },
    });
  } catch (err) {
    self.postMessage({
      type: "error",
      message: err instanceof Error ? err.message : String(err),
    });
  }
};