// Copyright (c) 2014-2024, The Monero Project
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// Parts of this file are originally copyright (c) 2012-2013 The Cryptonote developers

#include "base58.h"

#include <assert.h>
#include <string>
#include <vector>

#include "crypto/hash.h"
#include "int-util.h"
#include "varint.h"

namespace tools
{
  namespace base58
  {
    namespace
    {
      const char alphabet[] = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz";
      const size_t alphabet_size = sizeof(alphabet) - 1;
      const size_t encoded_block_sizes[] = {0, 2, 3, 5, 6, 7, 9, 10, 11};
      const size_t full_block_size = sizeof(encoded_block_sizes) / sizeof(encoded_block_sizes[0]) - 1;
      const size_t full_encoded_block_size = encoded_block_sizes[full_block_size];
      const size_t addr_checksum_size = 4;

      struct reverse_alphabet
      {
        reverse_alphabet()
        {
          m_data.resize(alphabet[alphabet_size - 1] - alphabet[0] + 1, -1);

          for (size_t i = 0; i < alphabet_size; ++i)
          {
            size_t idx = static_cast<size_t>(alphabet[i] - alphabet[0]);
            m_data[idx] = static_cast<int8_t>(i);
          }
        }

        int operator()(char letter) const
        {
          size_t idx = static_cast<size_t>(letter - alphabet[0]);
          return idx < m_data.size() ? m_data[idx] : -1;
        }

        static reverse_alphabet instance;

      private:
        std::vector<int8_t> m_data;
      };

      reverse_alphabet reverse_alphabet::instance;

      struct decoded_block_sizes
      {
        decoded_block_sizes()
        {
          m_data.resize(encoded_block_sizes[full_block_size] + 1, -1);
          for (size_t i = 0; i <= full_block_size; ++i)
          {
            m_data[encoded_block_sizes[i]] = static_cast<int>(i);
          }
        }

        int operator()(size_t encoded_block_size) const
        {
          assert(encoded_block_size <= full_encoded_block_size);
          return m_data[encoded_block_size];
        }

        static decoded_block_sizes instance;

      private:
        std::vector<int> m_data;
      };

      decoded_block_sizes decoded_block_sizes::instance;

      uint64_t uint_8be_to_64(const uint8_t* data, size_t size)
      {
        assert(1 <= size && size <= sizeof(uint64_t));

        uint64_t res = 0;
        memcpy(reinterpret_cast<uint8_t*>(&res) + sizeof(uint64_t) - size, data, size);
        return SWAP64BE(res);
      }

      void uint_64_to_8be(uint64_t num, size_t size, uint8_t* data)
      {
        assert(1 <= size && size <= sizeof(uint64_t));

        uint64_t num_be = SWAP64BE(num);
        memcpy(data, reinterpret_cast<uint8_t*>(&num_be) + sizeof(uint64_t) - size, size);
      }

      void encode_block(const char* block, size_t size, char* res)
      {
        assert(1 <= size && size <= full_block_size);

        uint64_t num = uint_8be_to_64(reinterpret_cast<const uint8_t*>(block), size);
        int i = static_cast<int>(encoded_block_sizes[size]) - 1;
        while (0 < num)
        {
          uint64_t remainder = num % alphabet_size;
          num /= alphabet_size;
          res[i] = alphabet[remainder];
          --i;
        }
      }

      bool decode_block(const char* block, size_t size, char* res)
      {
        assert(1 <= size && size <= full_encoded_block_size);

        int res_size = decoded_block_sizes::instance(size);
        if (res_size <= 0)
          return false; // Invalid block size

        uint64_t res_num = 0;
        uint64_t order = 1;
        for (size_t i = size - 1; i < size; --i)
        {
          int digit = reverse_alphabet::instance(block[i]);
          if (digit < 0)
            return false; // Invalid symbol

          uint64_t product_hi;
          uint64_t tmp = res_num + mul128(order, digit, &product_hi);
          if (tmp < res_num || 0 != product_hi)
            return false; // Overflow

          res_num = tmp;
          order *= alphabet_size; // Never overflows, 58^10 < 2^64
        }

        if (static_cast<size_t>(res_size) < full_block_size && (UINT64_C(1) << (8 * res_size)) <= res_num)
          return false; // Overflow

        uint_64_to_8be(res_num, res_size, reinterpret_cast<uint8_t*>(res));

        return true;
      }
    }

    std::string encode(const std::string& data)
    {
      if (data.empty())
        return std::string();

      size_t full_block_count = data.size() / full_block_size;
      size_t last_block_size = data.size() % full_block_size;
      size_t res_size = full_block_count * full_encoded_block_size + encoded_block_sizes[last_block_size];

      std::string res(res_size, alphabet[0]);
      for (size_t i = 0; i < full_block_count; ++i)
      {
        encode_block(data.data() + i * full_block_size, full_block_size, &res[i * full_encoded_block_size]);
      }

      if (0 < last_block_size)
      {
        encode_block(data.data() + full_block_count * full_block_size, last_block_size, &res[full_block_count * full_encoded_block_size]);
      }

      return res;
    }

    bool decode(const std::string& enc, std::string& data)
    {
      if (enc.empty())
      {
        data.clear();
        return true;
      }

      size_t full_block_count = enc.size() / full_encoded_block_size;
      size_t last_block_size = enc.size() % full_encoded_block_size;
      int last_block_decoded_size = decoded_block_sizes::instance(last_block_size);
      if (last_block_decoded_size < 0)
        return false; // Invalid enc length
      size_t data_size = full_block_count * full_block_size + last_block_decoded_size;

      data.resize(data_size, 0);
      for (size_t i = 0; i < full_block_count; ++i)
      {
        if (!decode_block(enc.data() + i * full_encoded_block_size, full_encoded_block_size, &data[i * full_block_size]))
          return false;
      }

      if (0 < last_block_size)
      {
        if (!decode_block(enc.data() + full_block_count * full_encoded_block_size, last_block_size,
          &data[full_block_count * full_block_size]))
          return false;
      }

      return true;
    }

    std::string encode_addr(uint64_t tag, const std::string& data)
    {
      std::string buf = get_varint_data(tag);
      buf += data;
      crypto::hash hash = crypto::cn_fast_hash(buf.data(), buf.size());
      const char* hash_data = reinterpret_cast<const char*>(&hash);
      buf.append(hash_data, addr_checksum_size);
      return encode(buf);
    }

    bool decode_addr(const std::string &addr, uint64_t& tag, std::string& data)
    {
      std::string addr_data;
      bool r = decode(addr, addr_data);
      if (!r) return false;
      if (addr_data.size() <= addr_checksum_size) return false;

      std::string checksum(addr_checksum_size, '\0');
      checksum = addr_data.substr(addr_data.size() - addr_checksum_size);

      addr_data.resize(addr_data.size() - addr_checksum_size);
      crypto::hash hash = crypto::cn_fast_hash(addr_data.data(), addr_data.size());
      std::string expected_checksum(reinterpret_cast<const char*>(&hash), addr_checksum_size);
      if (expected_checksum != checksum) return false;

      int read = tools::read_varint(addr_data.begin(), addr_data.end(), tag);
      if (read <= 0) return false;

      data = addr_data.substr(read);
      return true;
    }
  }
}