/*    This file is part of the Gudhi Library - https://gudhi.inria.fr/ - which is released under MIT.
 *    See file LICENSE or go to https://gudhi.inria.fr/licensing/ for full license details.
 *    Author(s):       Siargey Kachanovich
 *
 *    Copyright (C) 2016 Inria
 *
 *    Modification(s):
 *      - YYYY/MM Author: Description of the modification
 */

#ifndef ACTIVE_WITNESS_ACTIVE_WITNESS_ITERATOR_H_
#define ACTIVE_WITNESS_ACTIVE_WITNESS_ITERATOR_H_

#include <boost/iterator/iterator_facade.hpp>
#include <list>

namespace Gudhi {

namespace witness_complex {

/** \brief Iterator in the nearest landmark list.
 *  \details After the iterator reaches the end of the list,
 *          the list is augmented by a (nearest landmark, distance) pair if possible.
 *          If all the landmarks are present in the list, iterator returns the specific end value
 *          of the corresponding 'Active_witness' object.
 */
template< typename Active_witness,
          typename Id_distance_pair,
          typename INS_iterator >
class Active_witness_iterator
  : public boost::iterator_facade< Active_witness_iterator <Active_witness, Id_distance_pair, INS_iterator>,
                                   Id_distance_pair const,
                                   boost::forward_traversal_tag,
                                   Id_distance_pair const> {
  friend class boost::iterator_core_access;

  typedef typename std::list<Id_distance_pair>::iterator Pair_iterator;
  typedef typename Gudhi::witness_complex::Active_witness_iterator<Active_witness,
                                                                   Id_distance_pair,
                                                                   INS_iterator> Iterator;

  Active_witness *aw_;
  Pair_iterator lh_;  // landmark handle
  bool is_end_;  // true only if the pointer is end and there are no more neighbors to add

 public:
  Active_witness_iterator(Active_witness* aw)
    : aw_(aw), lh_(aw_->nearest_landmark_table_.end()), is_end_(true) {
  }

  Active_witness_iterator(Active_witness* aw, const Pair_iterator& lh)
    : aw_(aw), lh_(lh) {
    is_end_ = false;
    if (lh_ == aw_->nearest_landmark_table_.end()) {
      if (aw_->iterator_next_ == aw_->iterator_end_) {
        is_end_ = true;
      } else {
        aw_->nearest_landmark_table_.push_back(*aw_->iterator_next_);
        lh_ = --aw_->nearest_landmark_table_.end();
        ++(aw_->iterator_next_);
      }
    }
  }

 private :
  Id_distance_pair& dereference() const {
    return *lh_;
  }

  bool equal(const Iterator& other) const {
    return (is_end_ == other.is_end_) || (lh_ == other.lh_);
  }

  void increment() {
    // the neighbor search can't be at the end iterator of a list
    GUDHI_CHECK(!is_end_ && lh_ != aw_->nearest_landmark_table_.end(),
                std::logic_error("Wrong active witness increment."));
    // if the id of the current landmark is the same as the last one

    lh_++;
    if (lh_ == aw_->nearest_landmark_table_.end()) {
      if (aw_->iterator_next_ == aw_->iterator_end_) {
        is_end_ = true;
      } else {
        aw_->nearest_landmark_table_.push_back(*aw_->iterator_next_);
        lh_ = std::prev(aw_->nearest_landmark_table_.end());
        ++(aw_->iterator_next_);
      }
    }
  }
};

}  // namespace witness_complex
}  // namespace Gudhi

#endif  // ACTIVE_WITNESS_ACTIVE_WITNESS_ITERATOR_H_
