/**
	This file is a part of rexy's general purpose library
	Copyright (C) 2022 rexy712

	This program is free software: you can redistribute it and/or modify
	it under the terms of the GNU General Public License as published by
	the Free Software Foundation, either version 3 of the License, or
	(at your option) any later version.

	This program is distributed in the hope that it will be useful,
	but WITHOUT ANY WARRANTY; without even the implied warranty of
	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
	GNU General Public License for more details.

	You should have received a copy of the GNU General Public License
	along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

#ifndef REXY_DETAIL_FORMAT_UTF_ITERATOR_TPP
#define REXY_DETAIL_FORMAT_UTF_ITERATOR_TPP

namespace rexy::fmt::detail{

	template<class Char>
	class utf8_iterator
	{
	private:
		const Char* m_start = nullptr;
		const Char* m_last = nullptr;
		const Char* m_next = nullptr;
		char32_t m_value = 0;

	public:
		constexpr utf8_iterator(const Char* first, const Char* last):
			m_start(first), m_last(last)
		{
			m_next = convert_codepoint(m_start, m_last, m_value);
		}

		constexpr utf8_iterator& operator++(void){
			m_start = m_next;
			if(m_start != m_last){
				m_next = convert_codepoint(m_start, m_last, m_value);
			}
			return *this;
		}
		constexpr utf8_iterator operator++(int){
			auto tmp = *this;
			++(*this);
			return tmp;
		}
		constexpr char32_t operator*(void)const{
			return m_value;
		}
		constexpr bool valid(void)const{
			return m_start != m_last;
		}
		constexpr std::size_t byte_count(void)const{
			return m_next - m_start;
		}

	private:
		static constexpr const Char* convert_codepoint(const Char* first, const Char* last, char32_t& codepoint){
			const std::size_t maxlen = last - first;
			if((*first & 0x80) == 0){
				codepoint = first[0];
				return first + 1;
			}else if((*first & 0xE0) == 0xC0 && maxlen > 1){
				codepoint = ((first[0] & 0x1F) << 6);
				codepoint += (first[1] & 0x3F);
				return first + 2;
			}else if((*first & 0xF0) == 0xE0 && maxlen > 2){
				codepoint = ((first[0] & 0x0F) << 12);
				codepoint += ((first[1] & 0x3F) << 6);
				codepoint += (first[2] & 0x3F);
				return first + 3;
			}else if((*first & 0xF8) == 0xF0 && maxlen > 3){
				codepoint = ((first[0] & 0x07) << 18);
				codepoint += ((first[1] & 0x3F) << 12);
				codepoint += (first[2] & 0x3F) << 6;
				codepoint += (first[3] & 0x3F);
				return first + 4;
			}
			codepoint = 0;
			return first;
		}
	};

}

#endif