cpp-useful-iterators/include/iterator/join_iterator.hpp

//
//  join_iterator.hpp
//  iterator
//
//  Created by Sam Jaffe on 2/7/17.
//

#pragma once

#include "iterator_fwd.hpp"
#include "end_aware_iterator.hpp"

#include <iterator>

namespace iterator {
  template <typename MetaIterator>
  class joining_iterator {
  public:
    using join_iter = MetaIterator;
    using joinable_type = typename join_iter::value_type;
    using iter_type = detail::value_iterator<MetaIterator>;
    
    using value_type = typename std::iterator_traits<iter_type>::value_type;
    using reference = typename std::iterator_traits<iter_type>::reference;
    using pointer = typename std::iterator_traits<iter_type>::pointer;
    using difference_type = typename std::iterator_traits<iter_type>::difference_type;
    using iterator_category = std::forward_iterator_tag;
  public:
    explicit joining_iterator( ) = default;
    
    template <typename I>
    joining_iterator( joining_iterator<I> const & other )
    : joiner_(other.join_iterator()), iterator_(other.element_iterator()) {
      
    }
    
    joining_iterator( end_aware_iterator<join_iter> join ) : joining_iterator(join, {}, true) {}
    joining_iterator( end_aware_iterator<join_iter> join, end_aware_iterator<iter_type> elem, bool update = false )
    : joiner_(join), iterator_(elem) {
      if ( update ) { update_iterator(); }
    }
    
    joining_iterator & operator++() {
      if ( (++iterator_).done() ) {
        ++joiner_;
        update_iterator();
      }
      return *this;
    }
    
    joining_iterator operator++(int) {
      joining_iterator tmp{*this};
      operator++();
      return tmp;
    }
    
    reference operator*() const { return iterator_.operator*(); }
    pointer operator->() const { return iterator_.operator->(); }
    
    bool operator==(joining_iterator const & other) const {
      return joiner_ == other.joiner_ && iterator_ == other.iterator_;
    }
    
    bool operator!=(joining_iterator const & other) {
      return !(operator==(other));
    }
    
    end_aware_iterator<join_iter> join_iterator() const { return joiner_; }
    end_aware_iterator<iter_type> element_iterator() const { return iterator_; }
  private:
    void update_iterator() {
      while ( !joiner_.done() && std::begin(*joiner_) == std::end(*joiner_) ) {
        ++joiner_;
      }
      if ( !joiner_.done() ) {
        iterator_ = { std::begin(*joiner_), std::end(*joiner_) };
      }
    }
    
    end_aware_iterator<join_iter> joiner_;
    end_aware_iterator<iter_type> iterator_;
  };
}