/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
/**
 * Copyright (C) 2014 Named Data Networking Project
 * See COPYING for copyright and distribution information.
 */

// Name Tree (Name Prefix Hash Table)

#ifndef NFD_TABLE_NAME_TREE_HPP
#define NFD_TABLE_NAME_TREE_HPP

#include "common.hpp"
#include "name-tree-entry.hpp"

namespace nfd {
namespace name_tree {

/**
 * @brief Compute the hash value of the given name prefix.
 * @todo 1) have another parameter that specifies the number of components
 * 2) optimize the hash function to return a list of have values for all
 * the (or a certain number of, like a batch operation) prefixes. 3) move
 * the hash-related code to a separate file in /core or ndn-cpp-dev lib.
 */
uint32_t
hashName(const Name& prefix);

/// a predicate to accept or reject an Entry in find operations
typedef function<bool (const Entry& entry)> EntrySelector;

struct AnyEntry {
  bool
  operator()(const Entry& entry)
  {
    return true;
  }
};

} // namespace name_tree

/**
 * @brief Class Name Tree
 */
class NameTree : noncopyable
{
public:
  explicit
  NameTree(size_t nBuckets);

  ~NameTree();

  /**
   * @brief Get the number of occupied entries in the Name Tree
   */
  size_t
  size() const;

  /**
   * @brief Get the number of buckets in the Name Tree (NPHT)
   * @details The number of buckets is the one that used to create the hash
   * table, i.e., m_nBuckets.
   */
  size_t
  getNBuckets() const;

  /**
   * @brief Look for the Name Tree Entry that contains this name prefix.
   * @details Starts from the shortest name prefix, and then increase the
   * number of name components by one each time. All non-existing Name Tree
   * Entries will be created.
   * @param prefix The querying name prefix.
   * @return The pointer to the Name Tree Entry that contains this full name
   * prefix.
   */
  shared_ptr<name_tree::Entry>
  lookup(const Name& prefix);

  /**
   * @brief Exact match lookup for the given name prefix.
   * @return a null shared_ptr if this prefix is not found;
   * otherwise return the Name Tree Entry address
   */
  shared_ptr<name_tree::Entry>
  findExactMatch(const Name& prefix) const;

  /**
   * @brief Erase a Name Tree Entry if this entry is empty.
   * @details If a Name Tree Entry contains no Children, no FIB, no PIT, and
   * no Measurements entries, then it can be erased. In addition, its parent entry
   * will also be examined by following the parent pointer until all empty entries
   * are erased.
   * @param entry The pointer to the entry to be erased. The entry pointer should
   * returned by the findExactMatch(), lookup(), or findLongestPrefixMatch() functions.
   */
  bool
  eraseEntryIfEmpty(shared_ptr<name_tree::Entry> entry);

  /**
   * @brief Longest prefix matching for the given name
   * @details Starts from the full name string, reduce the number of name component
   * by one each time, until an Entry is found.
   */
  shared_ptr<name_tree::Entry>
  findLongestPrefixMatch(const Name& prefix,
                         const name_tree::EntrySelector& entrySelector = name_tree::AnyEntry());

  /**
   * @brief Resize the hash table size when its load factor reaches a threshold.
   * @details As we are currently using a hand-written hash table implementation
   * for the Name Tree, the hash table resize() function should be kept in the
   * name-tree.hpp file.
   * @param newNBuckets The number of buckets for the new hash table.
   */
  void
  resize(size_t newNBuckets);

  /**
   * @brief Enumerate all the name prefixes stored in the Name Tree.
   */
  shared_ptr<std::vector<shared_ptr<name_tree::Entry> > >
  fullEnumerate(const name_tree::EntrySelector& entrySelector = name_tree::AnyEntry());

  /**
   * @brief Enumerate all the name prefixes under a specific name prefix
   * @todo It might be better to have functions like fullEnemerateFib() to reduce the
   * number of entries stored in the vector.
   */
  shared_ptr<std::vector<shared_ptr<name_tree::Entry> > >
  partialEnumerate(const Name& prefix,
                   const name_tree::EntrySelector& entrySelector = name_tree::AnyEntry());

  /**
   * @brief Dump all the information stored in the Name Tree for debugging.
   */
  void
  dump(std::ostream& output);

private:
  size_t m_nItems;  // Number of items being stored
  size_t m_nBuckets; // Number of hash buckets
  double m_loadFactor;
  size_t m_resizeThreshold;
  int m_resizeFactor;
  name_tree::Node** m_buckets; // Name Tree Buckets in the NPHT

  /**
   * @brief Create a Name Tree Entry if it does not exist, or return the existing
   * Name Tree Entry address.
   * @details Called by lookup() only.
   * @return The first item is the Name Tree Entry address, the second item is
   * a bool value indicates whether this is an old entry (false) or a new
   * entry (true).
   */
  std::pair<shared_ptr<name_tree::Entry>, bool>
  insert(const Name& prefix);

  /**
   * @brief Helper function for partialEnumerate()
   */
  void
  partialEnumerateAddChildren(shared_ptr<name_tree::Entry> entry,
                              const name_tree::EntrySelector& entrySelector,
                              std::vector<shared_ptr<name_tree::Entry> >& results);

};

inline size_t
NameTree::size() const
{
  return m_nItems;
}

inline size_t
NameTree::getNBuckets() const
{
  return m_nBuckets;
}

} // namespace nfd

#endif // NFD_TABLE_NAME_TREE_HPP