Crow/utility.h

#pragma once

#include <stdint.h>
#include <stdexcept>

namespace flask
{
	namespace black_magic
	{
		struct OutOfRange
		{
			OutOfRange(unsigned pos, unsigned length) {}
		};
		constexpr unsigned requires_in_range( unsigned i, unsigned len )
		{
			return i >= len ? throw OutOfRange(i, len) : i;
		}

		class const_str
		{
			const char * const begin_;
			unsigned size_;

			public:
			template< unsigned N >
				constexpr const_str( const char(&arr)[N] ) : begin_(arr), size_(N - 1) {
					static_assert( N >= 1, "not a string literal");
				}
			constexpr char operator[]( unsigned i ) const { 
				return requires_in_range(i, size_), begin_[i]; 
			}

			constexpr operator const char *() const { 
				return begin_; 
			}

			constexpr unsigned size() const { 
				return size_; 
			}
		};


		constexpr unsigned find_closing_tag(const_str s, unsigned p)
		{
			return s[p] == '>' ? p : find_closing_tag(s, p+1);
		}

        constexpr bool is_valid(const_str s, unsigned i = 0, int f = 0)
        {
            return 
                i == s.size()
                    ? f == 0 :
                f < 0 || f >= 2
                    ? false :
                s[i] == '<'
                    ? is_valid(s, i+1, f+1) :
                s[i] == '>'
                    ? is_valid(s, i+1, f-1) :
                is_valid(s, i+1, f);
        }

		constexpr int count(const_str s, unsigned i=0)
		{
			return i == s.size() ? 0 : s[i] == '<' ? 1+count(s,i+1) : count(s,i+1);
		}

        constexpr bool is_equ_n(const_str a, unsigned ai, const_str b, unsigned bi, unsigned n)
        {
            return 
                ai + n > a.size() || bi + n > b.size() 
                    ? false :
                n == 0 
                    ? true : 
                a[ai] != b[bi] 
                    ? false : 
                is_equ_n(a,ai+1,b,bi+1,n-1);
        }

        constexpr bool is_int(const_str s, unsigned i)
        {
            return is_equ_n(s, i, "<int>", 0, 5);
        }

        constexpr bool is_uint(const_str s, unsigned i)
        {
            return is_equ_n(s, i, "<uint>", 0, 6);
        }

        constexpr bool is_float(const_str s, unsigned i)
        {
            return is_equ_n(s, i, "<float>", 0, 7) ||
                is_equ_n(s, i, "<double>", 0, 8);
        }

        constexpr bool is_str(const_str s, unsigned i)
        {
            return is_equ_n(s, i, "<str>", 0, 5);
        }

        constexpr bool is_path(const_str s, unsigned i)
        {
            return is_equ_n(s, i, "<path>", 0, 6);
        }

        constexpr uint64_t get_parameter_tag(const_str s, unsigned p = 0)
        {
            return
                p == s.size() 
                    ?  0 :
                s[p] == '<' ? ( 
                    is_int(s, p)
                        ? get_parameter_tag(s, find_closing_tag(s, p)) * 6 + 1 :
                    is_uint(s, p)
                        ? get_parameter_tag(s, find_closing_tag(s, p)) * 6 + 2 :
                    is_float(s, p)
                        ? get_parameter_tag(s, find_closing_tag(s, p)) * 6 + 3 :
                    is_str(s, p)
                        ? get_parameter_tag(s, find_closing_tag(s, p)) * 6 + 4 :
                    is_path(s, p)
                        ? get_parameter_tag(s, find_closing_tag(s, p)) * 6 + 5 :
                    throw std::runtime_error("invalid parameter type")
                    ) : 
                get_parameter_tag(s, p+1);
        }

        template <typename ... T>
        struct S
        {
            template <typename U>
            using push = S<U, T...>;
            template <typename U>
            using push_back = S<T..., U>;
            template <template<typename ... Args> class U>
            using rebind = U<T...>;
        };
template <typename F, typename Set>
        struct CallHelper;
        template <typename F, typename ...Args>
        struct CallHelper<F, S<Args...>>
        {
            template <typename F1, typename ...Args1, typename = 
                decltype(std::declval<F1>()(std::declval<Args1>()...))
                >
            static char __test(int);

            template <typename ...>
            static int __test(...);

            static constexpr bool value = sizeof(__test<F, Args...>(0)) == sizeof(char);
        };


        template <int N>
        struct single_tag_to_type
        {
        };

        template <>
        struct single_tag_to_type<1>
        {
            using type = int64_t;
        };

        template <>
        struct single_tag_to_type<2>
        {
            using type = uint64_t;
        };

        template <>
        struct single_tag_to_type<3>
        {
            using type = double;
        };

        template <>
        struct single_tag_to_type<4>
        {
            using type = std::string;
        };

        template <>
        struct single_tag_to_type<5>
        {
            using type = std::string;
        };


        template <uint64_t Tag> 
        struct arguments
        {
            using subarguments = typename arguments<Tag/6>::type;
            using type = 
                typename subarguments::template push<typename single_tag_to_type<Tag%6>::type>;
        };

        template <> 
        struct arguments<0>
        {
            using type = S<>;
        };

	}
}