Function migrateBookRemoteState

packages/core/src/sync/sync-files.ts:831–964

* Bring the remote state for one book up to the current layout: * - If a folder exists under a stale name (title changed) → rename folder contents. * - If only legacy `/file/{id}.ext` / `/cover/{id}.ext` exist → move them into the per-book folder. * - Otherwise inspect the existing folder t

(
  backend: ISyncBackend,
  info: BookInfo,
  listings: RemoteListings,
)

 * Returns whether file/cover are now present at their *new* canonical paths.
 */
async function migrateBookRemoteState(
  backend: ISyncBackend,
  info: BookInfo,
  listings: RemoteListings,
): Promise<MigrationResult> {
  const { book } = info;
  const existingFolderName = listings.bookDirByBookId.get(book.id);
  let fileAtNew = false;
  let coverAtNew = false;
  let fileSize = listings.fileSizeByBookId.get(book.id);
  let coverSize = listings.coverSizeByBookId.get(book.id);

  if (existingFolderName) {
    if (existingFolderName !== info.expectedFolderName) {
      // Title changed (or sanitized form changed): rename folder by moving every child.
      const oldDir = `${REMOTE_BOOKS_ROOT}/${existingFolderName}`;
      let oldFiles: RemoteFile[] = [];
      try {
        oldFiles = await backend.listDir(oldDir);
      } catch (e) {
        console.warn(`[Sync] Failed to list old book folder ${oldDir}:`, e);
      }
      for (const f of oldFiles) {
        if (f.isDirectory) continue;
        const ext = getExt(f.name);
        if (!ext) continue;
        const cover = isCoverFileName(f.name);
        const target = cover ? buildBookRemoteCover(book, ext) : buildBookRemoteFile(book, ext);
        try {
          await backend.move(`${oldDir}/${f.name}`, target);
          if (cover) {
            coverAtNew = true;
            if (isPositiveFiniteNumber(f.size)) coverSize = f.size;
          } else {
            fileAtNew = true;
            if (isPositiveFiniteNumber(f.size)) fileSize = f.size;
          }
        } catch (e) {
          console.warn(`[Sync] Folder-rename MOVE failed for ${book.id} (${f.name}):`, e);
          if (await backend.exists(target)) {
            try {
              await backend.delete(`${oldDir}/${f.name}`);
            } catch {}
            if (cover) {
              coverAtNew = true;
              if (isPositiveFiniteNumber(f.size)) coverSize = f.size;
            } else {
              fileAtNew = true;
              if (isPositiveFiniteNumber(f.size)) fileSize = f.size;
            }
          }
        }
      }
      try {
        await backend.delete(oldDir);
      } catch {}
      // Update in-memory map so orphan cleanup downstream doesn't see this as unknown.
      listings.bookDirByBookId.delete(book.id);