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_MAPPING_ID_H_
  #define CARTOGRAPHER_MAPPING_ID_H_
  
  #include <algorithm>
  #include <iostream>
  #include <iterator>
  #include <limits>
  #include <map>
  #include <memory>
  #include <ostream>
  #include <tuple>
  #include <vector>
  
  #include "cartographer/common/make_unique.h"
  #include "cartographer/common/port.h"
  #include "cartographer/common/time.h"
  #include "glog/logging.h"
  
  namespace cartographer {
  namespace mapping {
  
  // Uniquely identifies a trajectory node using a combination of a unique
  // trajectory ID and a zero-based index of the node inside that trajectory.
  struct NodeId {
    int trajectory_id;
    int node_index;
  
    bool operator==(const NodeId& other) const {
      return std::forward_as_tuple(trajectory_id, node_index) ==
             std::forward_as_tuple(other.trajectory_id, other.node_index);
    }
  
    bool operator!=(const NodeId& other) const { return !operator==(other); }
  
    bool operator<(const NodeId& other) const {
      return std::forward_as_tuple(trajectory_id, node_index) <
             std::forward_as_tuple(other.trajectory_id, other.node_index);
    }
  };
  
  inline std::ostream& operator<<(std::ostream& os, const NodeId& v) {
    return os << "(" << v.trajectory_id << ", " << v.node_index << ")";
  }
  
  // Uniquely identifies a submap using a combination of a unique trajectory ID
  // and a zero-based index of the submap inside that trajectory.
  struct SubmapId {
    int trajectory_id;
    int submap_index;
  
    bool operator==(const SubmapId& other) const {
      return std::forward_as_tuple(trajectory_id, submap_index) ==
             std::forward_as_tuple(other.trajectory_id, other.submap_index);
    }
  
    bool operator!=(const SubmapId& other) const { return !operator==(other); }
  
    bool operator<(const SubmapId& other) const {
      return std::forward_as_tuple(trajectory_id, submap_index) <
             std::forward_as_tuple(other.trajectory_id, other.submap_index);
    }
  };
  
  inline std::ostream& operator<<(std::ostream& os, const SubmapId& v) {
    return os << "(" << v.trajectory_id << ", " << v.submap_index << ")";
  }
  
  template <typename IteratorType>
  class Range {
   public:
    Range(const IteratorType& begin, const IteratorType& end)
        : begin_(begin), end_(end) {}
  
    IteratorType begin() const { return begin_; }
    IteratorType end() const { return end_; }
  
   private:
    IteratorType begin_;
    IteratorType end_;
  };
  
  // Reminiscent of std::map, but indexed by 'IdType' which can be 'NodeId' or
  // 'SubmapId'.
  // Note: This container will only ever contain non-empty trajectories. Trimming
  // the last remaining node of a trajectory drops the trajectory.
  template <typename IdType, typename DataType>
  class MapById {
   private:
    class MapByIndex;
  
   public:
    struct IdDataReference {
      IdType id;
      const DataType& data;
    };
  
    class ConstIterator {
     public:
      using iterator_category = std::bidirectional_iterator_tag;
      using value_type = IdDataReference;
      using difference_type = int64;
      using pointer = std::unique_ptr<const IdDataReference>;
      using reference = const IdDataReference&;
  
      explicit ConstIterator(const MapById& map_by_id, const int trajectory_id)
          : current_trajectory_(
                map_by_id.trajectories_.lower_bound(trajectory_id)),
            end_trajectory_(map_by_id.trajectories_.end()) {
        if (current_trajectory_ != end_trajectory_) {
          current_data_ = current_trajectory_->second.data_.begin();
          AdvanceToValidDataIterator();
        }
      }
  
      explicit ConstIterator(const MapById& map_by_id, const IdType& id)
          : current_trajectory_(map_by_id.trajectories_.find(id.trajectory_id)),
            end_trajectory_(map_by_id.trajectories_.end()) {
        if (current_trajectory_ != end_trajectory_) {
          current_data_ =
              current_trajectory_->second.data_.find(MapById::GetIndex(id));
          if (current_data_ == current_trajectory_->second.data_.end()) {
            current_trajectory_ = end_trajectory_;
          }
        }
      }
  
      IdDataReference operator*() const {
        CHECK(current_trajectory_ != end_trajectory_);
        return IdDataReference{
            IdType{current_trajectory_->first, current_data_->first},
            current_data_->second};
      }
  
      std::unique_ptr<const IdDataReference> operator->() const {
        return common::make_unique<const IdDataReference>(this->operator*());
      }
  
      ConstIterator& operator++() {
        CHECK(current_trajectory_ != end_trajectory_);
        ++current_data_;
        AdvanceToValidDataIterator();
        return *this;
      }
  
      ConstIterator& operator--() {
        while (current_trajectory_ == end_trajectory_ ||
               current_data_ == current_trajectory_->second.data_.begin()) {
          --current_trajectory_;
          current_data_ = current_trajectory_->second.data_.end();
        }
        --current_data_;
        return *this;
      }
  
      bool operator==(const ConstIterator& it) const {
        if (current_trajectory_ == end_trajectory_ ||
            it.current_trajectory_ == it.end_trajectory_) {
          return current_trajectory_ == it.current_trajectory_;
        }
        return current_trajectory_ == it.current_trajectory_ &&
               current_data_ == it.current_data_;
      }
  
      bool operator!=(const ConstIterator& it) const { return !operator==(it); }
  
     private:
      void AdvanceToValidDataIterator() {
        CHECK(current_trajectory_ != end_trajectory_);
        while (current_data_ == current_trajectory_->second.data_.end()) {
          ++current_trajectory_;
          if (current_trajectory_ == end_trajectory_) {
            return;
          }
          current_data_ = current_trajectory_->second.data_.begin();
        }
      }
  
      typename std::map<int, MapByIndex>::const_iterator current_trajectory_;
      typename std::map<int, MapByIndex>::const_iterator end_trajectory_;
      typename std::map<int, DataType>::const_iterator current_data_;
    };
  
    class ConstTrajectoryIterator {
     public:
      using iterator_category = std::bidirectional_iterator_tag;
      using value_type = int;
      using difference_type = int64;
      using pointer = int*;
      using reference = const int&;
  
      explicit ConstTrajectoryIterator(
          typename std::map<int, MapByIndex>::const_iterator current_trajectory)
          : current_trajectory_(current_trajectory) {}
  
      int operator*() const { return current_trajectory_->first; }
  
      ConstTrajectoryIterator& operator++() {
        ++current_trajectory_;
        return *this;
      }
  
      ConstTrajectoryIterator& operator--() {
        --current_trajectory_;
        return *this;
      }
  
      bool operator==(const ConstTrajectoryIterator& it) const {
        return current_trajectory_ == it.current_trajectory_;
      }
  
      bool operator!=(const ConstTrajectoryIterator& it) const {
        return !operator==(it);
      }
  
     private:
      typename std::map<int, MapByIndex>::const_iterator current_trajectory_;
    };
  
    // Appends data to a 'trajectory_id', creating trajectories as needed.
    IdType Append(const int trajectory_id, const DataType& data) {
      CHECK_GE(trajectory_id, 0);
      auto& trajectory = trajectories_[trajectory_id];
      CHECK(trajectory.can_append_);
      const int index =
          trajectory.data_.empty() ? 0 : trajectory.data_.rbegin()->first + 1;
      trajectory.data_.emplace(index, data);
      return IdType{trajectory_id, index};
    }
  
    // Returns an iterator to the element at 'id' or the end iterator if it does
    // not exist.
    ConstIterator find(const IdType& id) const {
      return ConstIterator(*this, id);
    }
  
    // Inserts data (which must not exist already) into a trajectory.
    void Insert(const IdType& id, const DataType& data) {
      CHECK_GE(id.trajectory_id, 0);
      CHECK_GE(GetIndex(id), 0);
      auto& trajectory = trajectories_[id.trajectory_id];
      trajectory.can_append_ = false;
      CHECK(trajectory.data_.emplace(GetIndex(id), data).second);
    }
  
    // Removes the data for 'id' which must exist.
    void Trim(const IdType& id) {
      auto& trajectory = trajectories_.at(id.trajectory_id);
      const auto it = trajectory.data_.find(GetIndex(id));
      CHECK(it != trajectory.data_.end());
      if (std::next(it) == trajectory.data_.end()) {
        // We are removing the data with the highest index from this trajectory.
        // We assume that we will never append to it anymore. If we did, we would
        // have to make sure that gaps in indices are properly chosen to maintain
        // correct connectivity.
        trajectory.can_append_ = false;
      }
      trajectory.data_.erase(it);
      if (trajectory.data_.empty()) {
        trajectories_.erase(id.trajectory_id);
      }
    }
  
    bool Contains(const IdType& id) const {
      return trajectories_.count(id.trajectory_id) != 0 &&
             trajectories_.at(id.trajectory_id).data_.count(GetIndex(id)) != 0;
    }
  
    const DataType& at(const IdType& id) const {
      return trajectories_.at(id.trajectory_id).data_.at(GetIndex(id));
    }
  
    DataType& at(const IdType& id) {
      return trajectories_.at(id.trajectory_id).data_.at(GetIndex(id));
    }
  
    // Support querying by trajectory.
    ConstIterator BeginOfTrajectory(const int trajectory_id) const {
      return ConstIterator(*this, trajectory_id);
    }
    ConstIterator EndOfTrajectory(const int trajectory_id) const {
      return BeginOfTrajectory(trajectory_id + 1);
    }
  
    // Returns 0 if 'trajectory_id' does not exist.
    size_t SizeOfTrajectoryOrZero(const int trajectory_id) const {
      return trajectories_.count(trajectory_id)
                 ? trajectories_.at(trajectory_id).data_.size()
                 : 0;
    }
  
    // Returns Range object for range-based loops over the nodes of a trajectory.
    Range<ConstIterator> trajectory(const int trajectory_id) const {
      return Range<ConstIterator>(BeginOfTrajectory(trajectory_id),
                                  EndOfTrajectory(trajectory_id));
    }
  
    // Returns Range object for range-based loops over the trajectory IDs.
    Range<ConstTrajectoryIterator> trajectory_ids() const {
      return Range<ConstTrajectoryIterator>(
          ConstTrajectoryIterator(trajectories_.begin()),
          ConstTrajectoryIterator(trajectories_.end()));
    }
  
    ConstIterator begin() const { return BeginOfTrajectory(0); }
    ConstIterator end() const {
      return BeginOfTrajectory(std::numeric_limits<int>::max());
    }
  
    bool empty() const { return begin() == end(); }
  
    // Returns an iterator to the the first element in the container belonging to
    // trajectory 'trajectory_id' whose time is not considered to go before
    // 'time', or EndOfTrajectory(trajectory_id) if all keys are considered to go
    // before 'time'.
    ConstIterator lower_bound(const int trajectory_id, const common::Time& time) {
      if (SizeOfTrajectoryOrZero(trajectory_id) == 0) {
        return EndOfTrajectory(trajectory_id);
      }
  
      const std::map<int, DataType>& trajectory =
          trajectories_.at(trajectory_id).data_;
      if (std::prev(trajectory.end())->second.time() < time) {
        return EndOfTrajectory(trajectory_id);
      }
      auto left = trajectory.begin();
      auto right = std::prev(trajectory.end());
      while (left != right) {
        const int middle = left->first + (right->first - left->first) / 2;
        const auto lower_bound_middle = trajectory.lower_bound(middle);
        if (lower_bound_middle->second.time() < time) {
          left = std::next(lower_bound_middle);
        } else {
          right = lower_bound_middle;
        }
      }
  
      return ConstIterator(*this, IdType{trajectory_id, left->first});
    }
  
   private:
    struct MapByIndex {
      bool can_append_ = true;
      std::map<int, DataType> data_;
    };
  
    static int GetIndex(const NodeId& id) { return id.node_index; }
    static int GetIndex(const SubmapId& id) { return id.submap_index; }
  
    std::map<int, MapByIndex> trajectories_;
  };
  
  }  // namespace mapping
  }  // namespace cartographer
  
  #endif  // CARTOGRAPHER_MAPPING_ID_H_
  