hash_map.hpp

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/* MIT License
 
Copyright (c) 2021 Karel Burda
 
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
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The above copyright notice and this permission notice shall be included in all
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/*
 *  Modifications and Customizations
 *
 *  Copyright (C) 2025, Libre Space Foundation <http://libre.space>
 *
 *  This program is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 *  SPDX-License-Identifier: GNU General Public License v3.0 or later
 */
 
#pragma once
 
#include <array>
#include <cstddef>
#include <iterator>
#include <utility>
 
namespace satnogs::comms::utils
{

template <std::size_t N, typename K, typename V> class hash_map
{
public:
  using key_type = K;
  using value_type = V;
  using size_type = decltype(N);
  using data_type = std::array<std::pair<K, V>, N>;
  using const_iterator = typename data_type::const_iterator;

  template <typename... E>
  explicit constexpr hash_map(E &&...elements) noexcept
      : data{std::forward<E>(elements)...}
  {
    static_assert(N > 0, "N should be positive");
    static_assert(N == sizeof...(elements),
                  "Elements size doesn't match expected size of a hash-map");
  }

  [[nodiscard]] constexpr const_iterator
  find(const K &key) const noexcept
  {
    return search<0, N>(key);
  }

  [[nodiscard]] constexpr std::pair<bool, const V &>
  at(const K &key) const noexcept
  {
    const auto it = find(key);
 
    if (it != cend()) {
      return {true, it->second};
    }
 
    return {false, {}};
  }

  // NOLINTNEXTLINE(fuchsia-overloaded-operator)
  [[nodiscard]] constexpr const V &
  operator[](const K &key) const noexcept
  {
    return find(key)->second;
  }

  [[nodiscard]] constexpr bool
  contains(const K &key) const noexcept
  {
    return search<0, N>(key) != cend();
  }

  [[nodiscard]] constexpr size_type
  size() const noexcept
  {
    return data.size();
  }

  [[nodiscard]] constexpr const_iterator
  begin() const noexcept
  {
    return cbegin();
  }

  [[nodiscard]] constexpr const_iterator
  cbegin() const noexcept
  {
    return std::cbegin(data);
  }

  [[nodiscard]] constexpr const_iterator
  end() const noexcept
  {
    return cend();
  }

  [[nodiscard]] constexpr const_iterator
  cend() const noexcept
  {
    return std::cend(data);
  }

  [[nodiscard]] constexpr bool
  empty() const noexcept
  {
    return false;
  }

  [[nodiscard]] constexpr std::array<K, N>
  keys() const noexcept
  {
    return keys_impl(std::make_index_sequence<N>{});
  }
 
protected:
  using index_type = size_type;

  template <index_type L, index_type R>
  [[nodiscard]] constexpr const_iterator
  search(const K &key) const noexcept
  {
    if constexpr (L < R) {
      if (equal(data[L].first, key)) {
        return std::next(cbegin(), L);
      }
 
      return search<L + 1, R>(key);
    }
 
    return cend();
  }

  template <typename T = K>
  [[nodiscard]] constexpr bool
  equal(const T &lhs, const T &rhs) const noexcept
  {
    return lhs == rhs;
  }

  [[nodiscard]] constexpr bool
  equal(const char *lhs, const char *rhs) const noexcept
  {
    // NOLINTNEXTLINE(cppcoreguidelines-pro-bounds-pointer-arithmetic)
    return *lhs == *rhs && (*lhs == '\0' || equal(lhs + 1, rhs + 1));
  }
 
  template <const auto... KeyIdx>
  [[nodiscard]] constexpr std::array<K, N>
  keys_impl(std::index_sequence<KeyIdx...>) const
  {
    return {data[KeyIdx].first...};
  }
 
private:
  data_type data;
};
 
} // namespace satnogs::comms::utils