output_container.h

//
// Created by light on 20-1-8.
//

#ifndef MORDEN_C_OUTPUT_CONTAINER_H
#define MORDEN_C_OUTPUT_CONTAINER_H

#include <ostream>      // std::ostream
#include <type_traits>  // std::false_type/true_type/decay_t/is_same_v
#include <utility>      // std::declval/pair

// 检测是否是pair
template<typename T>
struct is_pair : std::false_type {
};
template<typename T, typename U>
struct is_pair<std::pair<T, U>> : std::true_type {
};
template<typename T>
inline constexpr bool is_pair_v = is_pair<T>::value;

// 检测输出函数是否存在
template<typename T>
struct has_output_function {
    template<class U>
    static auto output(U *ptr)
    -> decltype(std::declval<std::ostream &>() << *ptr,
            std::true_type());

    template<class U>
    static std::false_type output(...);

    static constexpr bool value =
            decltype(output<T>(nullptr))::value;
};

template<typename T>
inline constexpr bool has_output_function_v =
        has_output_function<T>::value;


enum CHARS {
    ORD,        // 其他类型
    CHAR,       // char 类型
    STRING      // string 类型
};

template<typename T>
int ischarOrString(T &elem) {
    using std::decay_t;
    using std::is_same_v;
    using element_type = decay_t<decltype(elem)>;
    constexpr bool is_char_v = is_same_v<element_type, char>;
    constexpr bool is_string_v = is_same_v<element_type, char *> ||
                                 is_same_v<element_type, const char *> ||
                                 is_same_v<element_type, std::string>;
    if (is_char_v)
        return CHAR;
    else if (is_string_v)
        return STRING;
    else
        return ORD;
}

template<typename T>
void output(T &elem, int type, std::ostream &os) {
    switch (type) {
        case CHAR:
            os << '\'' << elem << '\'';
            break;
        case STRING:
            os << '\"' << elem << '\"';
            break;
        case ORD:
            os << elem;
            break;
    }
}

template<typename T, typename Cont>
auto output_element(std::ostream &os, const T &element,
                    const Cont &)
-> typename std::enable_if<is_pair<typename Cont::value_type>::value, bool>::type {
    int ftype = ischarOrString(element.first);
    int stype = ischarOrString(element.second);

    output(element.first, ftype, os);
    os << " => ";
    output(element.second, stype, os);
    return true;
}

template<typename T, typename Cont>
auto output_element(std::ostream &os, const T &element,
                    const Cont &)
-> typename std::enable_if<!is_pair<typename Cont::value_type>::value, bool>::type {
    int etype = ischarOrString(element);
    output(element, etype, os);
    return false;
}

template<typename T, typename U>
std::ostream &operator<<(std::ostream &os, const std::pair<T, U> &pr) {
    os << '(' << pr.first << ", " << pr.second << ')';
    return os;
}

//template<typename T, typename Cont>
//auto output_element(std::ostream& os, const T& element,
//                    const Cont&, const std::true_type)
//-> decltype(std::declval<typename Cont::key_type>(), os)
//{
//    os << element.first << " => " << element.second;
//    return os;
//}
//
//template <typename T, typename Cont>
//auto output_element(std::ostream& os, const T& element,
//                    const Cont&, ...)
//-> decltype(os)
//{
//    os << element;
//    return os;
//}



// 针对没有输出函数的容器处理
template<typename T,
        typename = std::enable_if_t<!has_output_function_v<T>>>
auto operator<<(std::ostream &os, const T &container)
-> decltype(container.begin(), container.end(), os) {
    os << "{ ";
    if (!container.empty()) {
        bool on_first_element = true;
        for (auto elem:container) {
            if (!on_first_element) {
                os << ", ";
            } else {
                on_first_element = false;
            }
            output_element(os, elem, container);
        }
    }
    os << " }";
    return os;
}


#endif //MORDEN_C_OUTPUT_CONTAINER_H