metastring.hpp

/*!
 * \file metastring.hpp
 * \brief Compile time string implementation
 * \author Jari Ronkainen
 * \version 1.0.1
 *
 * Depends on core.hpp
 *
 */
#ifndef MUSH_METASTRING_HEADER
#define MUSH_METASTRING_HEADER

#include <cstdint>
#include <memory>

#include "core.hpp"

namespace mush
{
    template <size_t... Indices> struct indices {};

    template <typename A, typename B> struct concatenate_indices;
    template <size_t, size_t, typename = void> struct expand_indices;

    template <size_t... Is, size_t... Js>
    struct concatenate_indices<indices<Is...>, indices<Js...>>
    {
        using indices_type = indices<Is..., Js...>;
    };

    template <size_t A, size_t B>
    struct expand_indices<A, B, typename std::enable_if<A == B>::type>
    {
        using indices_type = indices<A>;
    };

    template <size_t A, size_t B>
    struct expand_indices<A, B, typename std::enable_if<A != B>::type>
    {
        static_assert(A < B, "A > B");
        using indices_type = typename concatenate_indices<
            typename expand_indices<A, (A + B) / 2>::indices_type,
            typename expand_indices<(A + B) / 2 + 1, B>::indices_type
        >::indices_type;
    };

    template <size_t A>
    struct make_indices : expand_indices<0, A-1>::indices_type {};

    template <>
    struct make_indices<0> : indices<> {};

    template <size_t A, size_t B>
    struct make_indices_range : expand_indices<A, B-1>::indices_type {};

    template <size_t A>
    struct make_indices_range<A, A> : indices<> {};

    template <IntegralType Num>
    constexpr size_t get_num_size(Num n)
    {
        if (n == 0)
            return 1;

        size_t digits = 0;
        while(n)
        {
            n /= 10;
            ++digits;
        }

        return digits;
    }

    template <IntegralType Num>
    constexpr char nthdigit(Num x, int n)
    {
        while(n--)
            x /= 10;

        return (x % 10) + '0';
    }
    
    template <char... Data>
    struct array_holder
    {
        constexpr static char data[sizeof...(Data)] = {Data...};
        constexpr static size_t size = sizeof...(Data);
    };

    constexpr IntegralType abs_val(IntegralType x)
    {
        return x < 0 ? -x : x; 
    }

    constexpr ssize_t digit_count(IntegralType x)
    {
        return x < 0 ? 1 + digit_count(-x) : x < 10 ? 1 : 1 + digit_count(x/10);
    }

    template <size_t Size, ssize_t Num, char... Args>
    struct numeric_builder
    {
        typedef typename numeric_builder<Size - 1, Num / 10, '0' + abs_val(Num) % 10, Args...>::type type;
    };

    template <ssize_t Num, char... Args>
    struct numeric_builder<2, Num, Args...>
    {
        typedef array_holder<Num < 0 ? '-' : '0' + Num / 10, '0' + abs_val(Num) % 10, Args...> type;
    };

    template <ssize_t Num, char... Args>
    struct numeric_builder<1, Num, Args...>
    {
        typedef array_holder<'0' + Num, Args...> type;
    };

    template <ssize_t N>
    struct numeric_string
    {
        typedef typename numeric_builder<digit_count(N), N, '\0'>::type type;
        constexpr static type value {};
    };

    template<ssize_t N>
    constexpr typename numeric_string<N>::type numeric_string<N>::value;

    template <size_t N>
    class metastring
    {
        private:
            template <size_t I, size_t... Indices>
            constexpr metastring(const char(&str)[I], indices<Indices...>) : data{str[Indices]..., '\0'} {}

            template <size_t... Is, size_t... Js, size_t I>
            constexpr metastring<N+I-1> append(indices<Is...>, indices<Js...>, const char(&cstr)[I]) const
            {
                static_assert(I > 0);
                const char new_data[] = {data[Is]..., cstr[Js]..., '\0'};
                return metastring<N+I-1>(new_data);
            }

            template <size_t... Indices>
            constexpr metastring<N+1> push_back(char c, indices<Indices...>) const
            {
                const char new_data[] = {data[Indices]..., c, '\0'};
                return metastring<N+1>(new_data);
            }

        public:
            char data[N + 1];

            using data_type = const char(&)[N + 1];

            constexpr int size() const { return N; }
            constexpr data_type c_str() const { return data; }

            constexpr metastring(const char (&str)[N+1]) : metastring(str,make_indices<N>()) {}

            constexpr char& operator[](size_t idx) { return data[idx]; }

            template <size_t I>
            constexpr metastring<N+I-1> append(const char(&cstr)[I]) const
            {
                static_assert(I > 0);
                return append(make_indices<N>(), make_indices<I-1>(), cstr);
            }

            template <size_t I>
            constexpr metastring<N+I> append(const metastring<I>& mstr) const
            {
                static_assert(I >= 0);
                return append(make_indices<N>(), make_indices<I>(), mstr.c_str());
            }

            template <bool Enabled, size_t I>
            constexpr auto append_if(const char(&cstr)[I]) const
            {
                if constexpr (Enabled == false)
                {
                    return *this;
                } else {
                    static_assert(I > 0);
                    return append(make_indices<N>(), make_indices<I-1>(), cstr);
                }
            }
            
            template <bool Enabled, size_t I>
            constexpr auto append_if(const metastring<I>& mstr) const
            {
                if constexpr (Enabled == false)
                {
                    return *this;
                } else {
                    static_assert(I > 0);
                    return append(make_indices<N>(), make_indices<I>(), mstr.c_str());
                }
            }

            constexpr metastring<N + 1> push_back(char c) const
            {
                return push_back(c, make_indices<N>());
            }
            
            friend inline std::ostream& operator<<(std::ostream& out, const metastring& val)
            {
                out << val.c_str();

                return out;
            }
    };

    template <size_t N>
    constexpr auto make_string(const char(&cstr)[N])
    {
        return metastring<N-1>(cstr);
    }

    template <size_t I, size_t J>
    constexpr metastring<I+J> operator+(const metastring<I>& first, const metastring<J>& second)
    {
        return first.append(second);
    }

    template <ssize_t Integer, size_t Size = get_num_size(Integer)>
    constexpr metastring<Size> integer_to_metastring()
    {
        return make_string(numeric_string<Integer>::value.data);
    }
}

#endif
/*
 Copyright (c) 2017 Jari Ronkainen

    This software is provided 'as-is', without any express or implied warranty.
    In no event will the authors be held liable for any damages arising from the
    use of this software.

    Permission is granted to anyone to use this software for any purpose, including
    commercial applications, and to alter it and redistribute it freely, subject to
    the following restrictions:

    1. The origin of this software must not be misrepresented; you must not claim
       that you wrote the original software. If you use this software in a product,
       an acknowledgment in the product documentation would be appreciated but is
       not required.

    2. Altered source versions must be plainly marked as such, and must not be
       misrepresented as being the original software.

    3. This notice may not be removed or altered from any source distribution.
*/