text: /*
   * Copyright 2016 The Cartographer Authors
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  #ifndef CARTOGRAPHER_SENSOR_COLLATOR_H_
  #define CARTOGRAPHER_SENSOR_COLLATOR_H_
  
  #include <functional>
  #include <memory>
  #include <unordered_map>
  #include <unordered_set>
  #include <vector>
  
  #include "cartographer/sensor/data.h"
  #include "cartographer/sensor/ordered_multi_queue.h"
  
  namespace cartographer {
  namespace sensor {
  
  class Collator {
   public:
    using Callback = std::function<void(const string&, std::unique_ptr<Data>)>;
  
    Collator() {}
  
    Collator(const Collator&) = delete;
    Collator& operator=(const Collator&) = delete;
  
    // Adds a trajectory to produce sorted sensor output for. Calls 'callback'
    // for each collated sensor data.
    void AddTrajectory(int trajectory_id,
                       const std::unordered_set<string>& expected_sensor_ids,
                       const Callback& callback);
  
    // Marks 'trajectory_id' as finished.
    void FinishTrajectory(int trajectory_id);
  
    // Adds 'data' for 'trajectory_id' to be collated. 'data' must contain valid
    // sensor data. Sensor packets with matching 'sensor_id' must be added in time
    // order.
    void AddSensorData(int trajectory_id, const string& sensor_id,
                       std::unique_ptr<Data> data);
  
    // Dispatches all queued sensor packets. May only be called once.
    // AddSensorData may not be called after Flush.
    void Flush();
  
    // Must only be called if at least one unfinished trajectory exists. Returns
    // the ID of the trajectory that needs more data before the Collator is
    // unblocked.
    int GetBlockingTrajectoryId() const;
  
   private:
    // Queue keys are a pair of trajectory ID and sensor identifier.
    OrderedMultiQueue queue_;
  
    // Map of trajectory ID to all associated QueueKeys.
    std::unordered_map<int, std::vector<QueueKey>> queue_keys_;
  };
  
  }  // namespace sensor
  }  // namespace cartographer
  
  #endif  // CARTOGRAPHER_SENSOR_COLLATOR_H_
  