Function getLastEventId

src/gep/assetStore.js:393–449

()

const LAST_EVENT_MAX_CHUNK = 4 * 1024 * 1024;

function getLastEventId() {
  try {
    const p = eventsPath();
    if (!fs.existsSync(p)) return null;
    const stat = fs.statSync(p);
    if (stat.size === 0) return null;

    const cap = Math.min(stat.size, LAST_EVENT_MAX_CHUNK);
    let chunkSize = Math.min(stat.size, LAST_EVENT_INITIAL_CHUNK);

    const fd = fs.openSync(p, 'r');
    try {
      while (true) {
        const buf = Buffer.alloc(chunkSize);
        const readPos = stat.size - chunkSize;
        fs.readSync(fd, buf, 0, chunkSize, readPos);

        // Drop the trailing newline(s) the writer appends so lastIndexOf('\n')
        // points to the boundary BEFORE the final line, not at end-of-file.
        const trimmedTail = buf.toString('utf8').replace(/\n+$/, '');
        const lastNl = trimmedTail.lastIndexOf('\n');

        // The chunk fully contains the last line when either we read from the
        // start of the file, or we found a newline that bounds the line on
        // the left. Otherwise the final line is bigger than the current chunk
        // and we must grow.
        if (readPos > 0 && lastNl < 0) {
          if (chunkSize < cap) {
            chunkSize = Math.min(cap, chunkSize * 2);
            continue;
          }
          return null;
        }

        const lastLine = (lastNl >= 0 ? trimmedTail.slice(lastNl + 1) : trimmedTail).trim();
        if (!lastLine) return null;

        let last;
        try {
          last = JSON.parse(lastLine);
        } catch (parseErr) {
          if (chunkSize < cap) {
            chunkSize = Math.min(cap, chunkSize * 2);
            continue;
          }
          throw parseErr;
        }
        return last && typeof last.id === 'string' ? last.id : null;
      }
    } finally {
      fs.closeSync(fd);
    }
  } catch (e) {
    console.warn('[AssetStore] Failed to read last event ID:', e && e.message || e);
    return null;
  }
}