tbx/include/utils/json.h

/*!
 * \file files.h
 * \brief
 *      File functionality header
 *
 * \copyright Copyright (C) 2021 Christos Choutouridis <christos@choutouridis.net>
 *
 * <dl class=\"section copyright\"><dt>License</dt><dd>
 * All Rights Reserved.
 *
 * NOTICE:  All information contained herein is, and remains
 * the property of Christos Choutouridis. The intellectual
 * and technical concepts contained herein are proprietary to
 * Christos Choutouridis and are protected by copyright law.
 * Dissemination of this information or reproduction of this material
 * is strictly forbidden unless prior written permission is obtained
 * from Christos Choutouridis.
 * </dd></dl>
 */
#ifndef JSON_H_
#define JSON_H_

#include <cstddef>
#include <cstdlib>
#include <cstring>
#include <cctype>
#include <type_traits>
#include <string_view>
#include <array>

using size_t = std::size_t;

struct jpair_t {
    std::string_view key;
    std::string_view value;
};

template<size_t N>
struct json_dec_t {

    using string_view = std::string_view;

    json_dec_t(const char* buffer, size_t size) noexcept :
    buffer_(buffer, size), valid_(true) {
        enum state_t {
            ST=0, KEY, COLON, VALUE, SP
        } state = ST;

        size_t pairs =0;
        char* begin = nullptr;
        int s =0;
        bool str_value = false;     // flag to indicate the value is string

        for (size_t i=0 ; i<size ; ++i) {
            switch (state) {
                case ST:
                    if (std::isspace(buffer[i]))
                        continue;   // skip white space
                    if (buffer[i] == '{')
                        state = KEY;
                    break;

                case KEY:
                    if (pairs >= N) {
                        valid_ = false;
                        break;
                    }
                    if (std::isspace(buffer[i]))
                        continue;   // skip white space
                    if (buffer[i] == '\"') {
                        if (!begin)
                            begin = (char*)&buffer[i+1];
                        else {
                            s = (char*)&buffer[i] - begin;
                            if (s > 0)
                                pairs_[pairs].key = std::string_view{begin, (size_t)s};
                            else
                                pairs_[pairs].key = std::string_view{};
                            begin =nullptr;
                            s =0;
                            state = COLON;
                        }
                    }
                    else if (buffer[i] == '}')
                        return;
                    break;

                case COLON:
                    if (std::isspace(buffer[i]))
                        continue;   // skip white space
                    if (buffer[i] == ':')
                        state = VALUE;
                    else {
                        valid_ = false;
                        return;
                    }
                    break;

                case VALUE:
                    if (pairs >= N) {
                        valid_ = false;
                        break;
                    }
                    if (!begin && std::isspace(buffer[i]))          // consume pre-spaces
                        continue;
                    else if (!begin && !std::isspace(buffer[i])) {  // first character
                        if (buffer[i] == '\"') {
                            begin = (char*)&buffer[i+1];
                            str_value = true;
                        }
                        else {
                            begin = (char*)&buffer[i];
                            str_value = false;
                        }
                    }
                    else if (begin) {
                        if (str_value && (buffer[i] == '\"')) {
                            s  = (char*)&buffer[i] - begin;
                            if (s > 0)
                                pairs_[pairs].value = std::string_view{begin, (size_t)s};
                            else
                                pairs_[pairs].value = std::string_view{};
                            ++pairs;
                            begin =nullptr;
                            s =0;
                            state = SP;
                        }
                        else if (!str_value && (std::isspace(buffer[i]) || buffer[i] == ',' || buffer[i] == '}')) {
                            s  = (char*)&buffer[i] - begin;
                            if (s > 0)
                                pairs_[pairs].value = std::string_view{begin, (size_t)s};
                            else
                                pairs_[pairs].value = std::string_view{};
                            ++pairs;
                            begin =nullptr;
                            s =0;
                            if (std::isspace(buffer[i]))
                                state = SP;
                            else if (buffer[i] == ',')
                                state = KEY;
                            else if (buffer[i] == '}')
                                return;
                        }
                    }
                    break;

                case SP:
                    if (std::isspace(buffer[i]))
                        continue;   // skip white space
                    else if (buffer[i] == ',')
                        state = KEY;
                    else if (buffer[i] == '}')
                        return;
                    else {
                        valid_ = false;
                        return;
                    }
                    break;
            }
        }
    }
    template<typename T>
    T get (const char* key) {
        T t{};
        for (auto& it : pairs_) {
            if (it.key.compare(key) == 0) {
                extract_(it.value, &t);
                break;
            }
        }
        return t;
    }
    bool is_valid() const { return valid_; }

private:
    /*!
     * Convert the text pointed by \c str to a value and store it to
     * \c value. The type of conversion is deduced by the compiler
     * \tparam  T       The type of the value
     * \param str       pointer to string with the value
     * \param value     pointer to converted value
     */
    void extract_(std::string_view str, bool* value) {
        *value = (
            !std::strncmp(str.data(), "true", str.size()) ||
            !std::strncmp(str.data(), "True", str.size()) ||
            !std::strncmp(str.data(), "TRUE", str.size()) ||
            !std::strncmp(str.data(), "1", str.size())
        ) ? true : false;
    }
    void extract_(std::string_view str, int* value) {
        *value = std::atoi(str.data());
    }
    void extract_(std::string_view str, unsigned int* value) {
        *value = (unsigned int)std::atoi(str.data());
    }
    void extract_(std::string_view str, long* value) {
        *value = std::atol(str.data());
    }
    void extract_(std::string_view str, unsigned long* value) {
        *value = (unsigned long)std::atol(str.data());
    }
    void extract_(std::string_view str, double* value) {
        *value = std::atof(str.data());
    }
    void extract_(std::string_view str, char** value) {
        *value = (char*)str.data();
    }
    void extract_(std::string_view str, string_view* value) {
        *value = str;
    }
    //! Specialization (as overload function) to handle void* types
    void extract_ (const char* str, void* value) noexcept {
        (void)*str; (void)value;
    }
private:
    std::string_view        buffer_;
    std::array<jpair_t, N>  pairs_;
    bool                    valid_;
};



#endif /* JSON_H_ */