text: // Copyright (c) 2014-2020, The Monero Project
  // Copyright (c) 2018-2021, The Scala Network Project
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  /*!
   * \file language_base.h
   * 
   * \brief Language Base class for Polymorphism.
   */
  
  #ifndef LANGUAGE_BASE_H
  #define LANGUAGE_BASE_H
  
  #include <vector>
  #include <unordered_map>
  #include <string>
  #include <boost/algorithm/string.hpp>
  #include "misc_log_ex.h"
  #include "fnv1.h"
  #include "common/utf8.h"
  
  /*!
   * \namespace Language
   * \brief Mnemonic language related namespace.
   */
  namespace Language
  {
    /*!
     * \brief Returns a string made of (at most) the first count characters in s.
     *        Assumes well formedness. No check is made for this.
     * \param  s               The string from which to return the first count characters.
     * \param  count           How many characters to return.
     * \return                 A string consisting of the first count characters in s.
     */
    template<typename T>
    inline T utf8prefix(const T &s, size_t count)
    {
      T prefix = "";
      size_t avail = s.size();
      const char *ptr = s.data();
      while (count-- && avail--)
      {
        prefix += *ptr++;
        while (avail && ((*ptr) & 0xc0) == 0x80)
        {
          prefix += *ptr++;
          --avail;
        }
      }
      return prefix;
    }
  
    struct WordHash
    {
      std::size_t operator()(const epee::wipeable_string &s) const
      {
        const epee::wipeable_string sc = tools::utf8canonical(s, [](wint_t c) -> wint_t { return std::towlower(c); });
        return epee::fnv::FNV1a(sc.data(), sc.size());
      }
    };
  
    struct WordEqual
    {
      bool operator()(const epee::wipeable_string &s0, const epee::wipeable_string &s1) const
      {
        const epee::wipeable_string s0c = tools::utf8canonical(s0, [](wint_t c) -> wint_t { return std::towlower(c); });
        const epee::wipeable_string s1c = tools::utf8canonical(s1, [](wint_t c) -> wint_t { return std::towlower(c); });
        return s0c == s1c;
      }
    };
  
    /*!
     * \class Base
     * \brief A base language class which all languages have to inherit from for
     * Polymorphism.
     */
    class Base
    {
    protected:
      enum {
        ALLOW_SHORT_WORDS = 1<<0,
        ALLOW_DUPLICATE_PREFIXES = 1<<1,
      };
      enum {
        NWORDS = 1626
      };
      std::vector<std::string> word_list; /*!< A pointer to the array of words */
      std::unordered_map<epee::wipeable_string, uint32_t, WordHash, WordEqual> word_map; /*!< hash table to find word's index */
      std::unordered_map<epee::wipeable_string, uint32_t, WordHash, WordEqual> trimmed_word_map; /*!< hash table to find word's trimmed index */
      std::string language_name; /*!< Name of language */
      std::string english_language_name; /*!< Name of language */
      uint32_t unique_prefix_length; /*!< Number of unique starting characters to trim the wordlist to when matching */
      /*!
       * \brief Populates the word maps after the list is ready.
       */
      void populate_maps(uint32_t flags = 0)
      {
        int ii;
        std::vector<std::string>::const_iterator it;
        if (word_list.size () != NWORDS)
          throw std::runtime_error("Wrong word list length for " + language_name);
        for (it = word_list.begin(), ii = 0; it != word_list.end(); it++, ii++)
        {
          word_map[*it] = ii;
          if ((*it).size() < unique_prefix_length)
          {
            if (flags & ALLOW_SHORT_WORDS)
              MINFO(language_name << " word '" << *it << "' is shorter than its prefix length, " << unique_prefix_length);
            else
              throw std::runtime_error("Too short word in " + language_name + " word list: " + *it);
          }
          epee::wipeable_string trimmed;
          if (it->length() > unique_prefix_length)
          {
            trimmed = utf8prefix(*it, unique_prefix_length);
          }
          else
          {
            trimmed = *it;
          }
          if (trimmed_word_map.find(trimmed) != trimmed_word_map.end())
          {
            if (flags & ALLOW_DUPLICATE_PREFIXES)
              MWARNING("Duplicate prefix in " << language_name << " word list: " << std::string(trimmed.data(), trimmed.size()));
            else
              throw std::runtime_error("Duplicate prefix in " + language_name + " word list: " + std::string(trimmed.data(), trimmed.size()));
          }
          trimmed_word_map[trimmed] = ii;
        }
      }
    public:
      Base(const char *language_name, const char *english_language_name, const std::vector<std::string> &words, uint32_t prefix_length):
        word_list(words),
        unique_prefix_length(prefix_length),
        language_name(language_name),
        english_language_name(english_language_name)
      {
      }
      virtual ~Base()
      {
      }
      void set_words(const char * const words[])
      {
        word_list.resize(NWORDS);
        for (size_t i = 0; i < NWORDS; ++i)
          word_list[i] = words[i];
      }
      /*!
       * \brief Returns a pointer to the word list.
       * \return A pointer to the word list.
       */
      const std::vector<std::string>& get_word_list() const
      {
        return word_list;
      }
      /*!
       * \brief Returns a pointer to the word map.
       * \return A pointer to the word map.
       */
      const std::unordered_map<epee::wipeable_string, uint32_t, WordHash, WordEqual>& get_word_map() const
      {
        return word_map;
      }
      /*!
       * \brief Returns a pointer to the trimmed word map.
       * \return A pointer to the trimmed word map.
       */
      const std::unordered_map<epee::wipeable_string, uint32_t, WordHash, WordEqual>& get_trimmed_word_map() const
      {
        return trimmed_word_map;
      }
      /*!
       * \brief Returns the name of the language.
       * \return Name of the language.
       */
      const std::string &get_language_name() const
      {
        return language_name;
      }
      /*!
       * \brief Returns the name of the language in English.
       * \return Name of the language.
       */
      const std::string &get_english_language_name() const
      {
        return english_language_name;
      }
      /*!
       * \brief Returns the number of unique starting characters to be used for matching.
       * \return Number of unique starting characters.
       */
      uint32_t get_unique_prefix_length() const
      {
        return unique_prefix_length;
      }
    };
  }
  
  #endif
  