cpp-json/json_common.hpp

//
//  json_common.h
//  json
//
//  Created by Sam Jaffe on 4/22/16.
//

#pragma once

#include <cstdint>
#include <cstdlib>
#include <stdexcept>
#include <string>

namespace json {
  using string_jt = std::string;
  using double_jt = double;
  using int_jt = int32_t;
  using uint_jt = uint32_t;
  using bool_jt = bool;
  
  class value;
  
  class malformed_json_exception :
  public std::domain_error {
    using std::domain_error::domain_error;
  };
  
  namespace {
    const constexpr json::int_jt INT_JT_MAX_LAST_DIGIT = (0x7FFFFFFF % 10);
    const constexpr json::int_jt INT_JT_MAX = json::uint_jt(-1) - 1;
    const constexpr json::int_jt INT_JT_MIN = json::int_jt(~(json::uint_jt(-1) / 2));
    const constexpr json::uint_jt INT_JT_OVER = json::uint_jt(INT_JT_MAX) + 1;
    const constexpr json::uint_jt UINT_JT_MAX = json::uint_jt(0) - 1;
    //  const constexpr json::uint_jt UINT_JT_MIN = 0;
  }
}

namespace json {
  namespace helper {
    const char get_next_element(char const*& data);
    char const * get_numeric_token_end(char const * start);
    
    /**
     * @throws json::malformed_json_exception
     */
    void advance_to_boundary(char const endtok, char const *& data);
    
    /**
     * @throws json::malformed_json_exception
     */
    std::string parse_string(char const * & data);
        
    template <typename T>
    void parse_string(T& json, char const * & data) {
      json = parse_string(data);
    }
    
    template <typename T>
    void parse_double(T& json, char const * & data) {
      json = atof(data);
      while (isdigit(*data)) { ++data; }
      if (*data == '.' || *data == 'e') { ++data; }
      while (isdigit(*data)) { ++data; }
   }
    
//    template <typename T>
//    void parse_integer(T& json, char const * & data) {
//      json = atoi(data);
//      while (isdigit(*data)) { ++data; }
//    }
    
    template <typename J>
    void parse_numeric(J & json, char const * & data) {
      char const * start = data;
      char const * const end = get_numeric_token_end(start);
      
      if (end == start) {
        throw malformed_json_exception("Expected any token, got nothing");
      }
      
      bool const negative = *start == '-';
      if (negative) ++start;
      
      uint_jt const threshold = (UINT_JT_MAX / 10);
      uint_jt val = 0;
      for (; start != end; ++start) {
        if (!isdigit(*start)) {
          helper::parse_double(json, data);
          return;
        }
        int_jt digit = static_cast<int_jt>(*start - '0');
        if (val >= threshold) {
          if (val > threshold || (start + 1) < end || digit > INT_JT_MAX_LAST_DIGIT) {
            helper::parse_double(json, data);
            return;
          }
        }
        val = (10 * val) + digit;
      }
      if (negative && val == INT_JT_OVER) {
        json = INT_JT_MIN;
      } else if (negative) {
        json = -int_jt(val);
      } else if (val <= uint_jt(INT_JT_MAX)) {
        json = int_jt(val);
      } else {
        json = val;
      }
      data = start;
    }
  }  
}