class OffsetTracker {
  constructor() {
    this.partitions = new Map();
  }

  add(topic, partition, offset) {
    const key = `${topic}-${partition}`;
    if (!this.partitions.has(key)) {
      this.partitions.set(key, { nextCommitOffset: null, done: new Set() });
    }

    const state = this.partitions.get(key);
    const numericOffset = Number(offset);
    if (!Number.isFinite(numericOffset)) return;

    if (state.nextCommitOffset === null) {
      state.nextCommitOffset = numericOffset;
    } else if (numericOffset < state.nextCommitOffset) {
      state.nextCommitOffset = numericOffset;
    }
  }

  markDone(topic, partition, offset) {
    const key = `${topic}-${partition}`;
    const state = this.partitions.get(key);
    if (!state) return null;

    const numericOffset = Number(offset);
    if (!Number.isFinite(numericOffset)) return null;

    state.done.add(numericOffset);

    if (state.nextCommitOffset === null) {
      state.nextCommitOffset = numericOffset;
    }

    let advanced = false;
    while (state.nextCommitOffset !== null && state.done.has(state.nextCommitOffset)) {
      state.done.delete(state.nextCommitOffset);
      state.nextCommitOffset += 1;
      advanced = true;
    }

    if (!advanced) return null;
    return state.nextCommitOffset;
  }

  clear() {
    this.partitions.clear();
  }
}

export { OffsetTracker };