// Copyright (c) 2007-2020  INRIA (France).
// All rights reserved.
//
// This file is part of CGAL (www.cgal.org).
//
// $URL$
// $Id$
// SPDX-License-Identifier: GPL-3.0-or-later OR LicenseRef-Commercial
//
// Author(s)     : Jackson Campolattaro, Cédric Portaneri, Tong Zhao

#ifndef CGAL_ORTHTREE_TRAVERSAL_CRITERION_H
#define CGAL_ORTHTREE_TRAVERSAL_CRITERION_H

#include <CGAL/license/Orthtree.h>

#include <iostream>
#include <boost/range/iterator_range.hpp>
#include <CGAL/Orthtree/Traversal_iterator.h>

namespace CGAL {

namespace Orthtrees {

/// \cond SKIP_IN_MANUAL

template <typename Node>
Node next_sibling(Node n) {

  // Passing null returns the first node
  if (n.is_null())
    return Node();

  // If this node has no parent, it has no siblings
  if (n.parent().is_null())
    return Node();

  // Find out which child this is
  std::size_t index = n.index().to_ulong();

  constexpr static int degree = Node::Degree::value;
  // Return null if this is the last child
  if (index == degree - 1)
    return Node();

  // Otherwise, return the next child
  return n.parent()[index + 1];
}

template <typename Node>
Node next_sibling_up(Node n) {

  if (n.is_null())
    return Node();

  Node up = n.parent();

  while (!up.is_null()) {

    if (!next_sibling(up).is_null())
      return next_sibling(up);

    up = up.parent();
  }

  return Node();
}

template <typename Node>
Node deepest_first_child(Node n) {

  if (n.is_null())
    return Node();

  // Find the deepest child on the left
  Node first = n;
  while (!first.is_leaf())
    first = first[0];
  return first;
}

/// \endcond

namespace Traversal {

/*!
  \ingroup PkgOrthtreeTraversal
  \brief walker for preorder traversal
 */
struct Preorder {

  /*!
   * \brief retrieve the first node of a tree in a preorder traversal, given the root
   *
   * \tparam Point_index
   * \param root
   * \return
   */
  template <typename Node>
  Node first(Node root) const {
    return root;
  }

  /*!
   * \brief retrieve the next node of a tree in a preorder traversal, given the current one
   *
   * \tparam Point_index
   * \param n
   * \return
   */
  template <typename Node>
  Node next(Node n) const {

    if (n.is_leaf()) {

      Node next = next_sibling(n);

      if (next.is_null())
        return next_sibling_up(n);

      return next;

    }
    else // Return the first child of this node
      return n[0];
  }
};

/*!
  \ingroup PkgOrthtreeTraversal
  \todo
 */
struct Postorder {

  /*!
   * \brief retrieve the first node of a tree in a postorder traversal, given the root
   *
   * \tparam Point_index
   * \param root
   * \return
   */
  template <typename Node>
  Node first(Node root) const {

    return deepest_first_child(root);
  }

  /*!
   * \brief retrieve the next node of a tree in a postorder traversal, given the current one
   *
   * \tparam Point_index
   * \param n
   * \return
   */
  template <typename Node>
  Node next(Node n) const {

    Node next = deepest_first_child(next_sibling(n));

    if (!next)
      next = n.parent();

    return next;
  }
};

/*!
  \ingroup PkgOrthtreeTraversal
  \brief walker for leaves-only traversal
 */
struct Leaves {

  /*!
   * \brief retrieve the first node of a tree in a leaves-only traversal, given the root
   *
   * \tparam Point_index
   * \param root
   * \return
   */
  template <typename Node>
  Node first(Node root) const {

    return deepest_first_child(root);
  }

  /*!
   * \brief retrieve the next node of a tree in a leaves-only traversal, given the current one
   *
   * \tparam Point_index
   * \param n
   * \return
   */
  template <typename Node>
  Node next(Node n) const {

    Node next = deepest_first_child(next_sibling(n));

    if (next.is_null())
      next = deepest_first_child(next_sibling_up(n));

    return next;
  }
};

} // Traversal
} // Orthtree
} // CGAL

#endif //CGAL_ORTHTREE_TRAVERSAL_CRITERION_H