// utf_iterators.hpp
// Copyright (c) 2015-2018 Ben Hanson (http://www.benhanson.net/)
// Inspired by http://utfcpp.sourceforge.net/
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file licence_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
#ifndef LEXERTL_UTF_ITERATORS_HPP
#define LEXERTL_UTF_ITERATORS_HPP

#include <iterator>

namespace lexertl
{
template<typename char_iterator, typename char_type>
class basic_utf8_in_iterator :
    public std::iterator<std::input_iterator_tag, char_type>
{
public:
    using value_type = char_type;
    using difference_type =
        typename std::iterator_traits<char_iterator>::difference_type;
    using iterator_category = std::forward_iterator_tag;

    basic_utf8_in_iterator() :
        _it(char_iterator()),
        _end(char_iterator()),
        _char(0)
    {
    }

    explicit basic_utf8_in_iterator(const char_iterator &it_,
        const char_iterator &end_) :
        _it(it_),
        _end(it_),
        _char(0)
    {
        if (it_ != end_)
        {
            next();
        }
    }

    char_type operator *() const
    {
        return _char;
    }

    bool operator ==(const basic_utf8_in_iterator &rhs_) const
    {
        return _it == rhs_._it;
    }

    bool operator !=(const basic_utf8_in_iterator &rhs_) const
    {
        return _it != rhs_._it;
    }

    basic_utf8_in_iterator &operator ++()
    {
        _it = _end;
        next();
        return *this;
    }

    basic_utf8_in_iterator operator ++(int)
    {
        basic_utf8_in_iterator temp_ = *this;

        _it = _end;
        next();
        return temp_;
    }

    basic_utf8_in_iterator operator +(const std::size_t count_) const
    {
        basic_utf8_in_iterator temp_ = *this;

        for (std::size_t i_ = 0; i_ < count_; ++i_)
        {
            ++temp_;
        }

        return temp_;
    }

    basic_utf8_in_iterator operator -(const std::size_t count_) const
    {
        basic_utf8_in_iterator temp_ = *this;

        for (std::size_t i_ = 0; i_ < count_; ++i_)
        {
            temp_._end = temp_._it;
            --temp_._it;

            while ((*temp_._it & 0xc0) == 0x80) --temp_._it;
        }

        temp_.next();
        return temp_;
    }

private:
    char_iterator _it;
    char_iterator _end;
    char_type _char;

    void next()
    {
        const char len_ = len(_it);
        char_type ch_ = *_it & 0xff;

        switch (len_)
        {
        case 1:
            _end = _it;
            ++_end;
            break;
        case 2:
            _end = _it;
            ++_end;

            if ((*_end & 0xc0) != 0x80) break;

            ch_ = (ch_ << 6 & 0x7ff) | (*_end & 0x3f);
            ++_end;
            break;
        case 3:
            _end = _it;
            ++_end;

            if ((*_end & 0xc0) != 0x80) break;

            ch_ = (ch_ << 12 & 0xffff) | ((*_end & 0xff) << 6 & 0xfff);
            ++_end;

            if ((*_end & 0xc0) != 0x80) break;

            ch_ |= *_end & 0x3f;
            ++_end;
            break;
        case 4:
            _end = _it;
            ++_end;

            if ((*_end & 0xc0) != 0x80) break;

            ch_ = (ch_ << 18 & 0x1fffff) | ((*_end & 0xff) << 12 & 0x3ffff);
            ++_end;

            if ((*_end & 0xc0) != 0x80) break;

            ch_ |= (*_end & 0xff) << 6 & 0xfff;
            ++_end;

            if ((*_end & 0xc0) != 0x80) break;

            ch_ |= *_end & 0x3f;
            ++_end;
            break;
        }

        _char = ch_;
    }

    char len(const char_iterator &it_) const
    {
        const unsigned char ch_ = *it_;

        return ch_ < 0x80 ? 1 :
            ch_ >> 5 == 0x06 ? 2 :
            ch_ >> 4 == 0x0e ? 3 :
            ch_ >> 3 == 0x1e ? 4 :
            1;
    }
};

template<typename char_iterator>
class basic_utf8_out_iterator :
    public std::iterator<std::input_iterator_tag, char>
{
public:
    using value_type = char;
    using difference_type =
        typename std::iterator_traits<char_iterator>::difference_type;
    using iterator_category = std::forward_iterator_tag;

    basic_utf8_out_iterator() :
        _count(0),
        _index(0)
    {
    }

    explicit basic_utf8_out_iterator(const char_iterator &it_,
        const char_iterator &end_) :
        _it(it_),
        _count(0),
        _index(0)
    {
        if (it_ != end_)
        {
            next();
        }
    }

    char operator *() const
    {
        return _bytes[_index];
    }

    bool operator ==(const basic_utf8_out_iterator &rhs_) const
    {
        return _it == rhs_._it;
    }

    bool operator !=(const basic_utf8_out_iterator &rhs_) const
    {
        return _it != rhs_._it;
    }

    basic_utf8_out_iterator &operator ++()
    {
        ++_index;

        if (_index >= _count)
        {
            ++_it;
            next();
        }

        return *this;
    }

    basic_utf8_out_iterator operator ++(int)
    {
        basic_utf8_out_iterator temp_ = *this;

        ++_index;

        if (_index >= _count)
        {
            ++_it;
            next();
        }

        return temp_;
    }

private:
    char_iterator _it;
    char _bytes[4];
    unsigned char _count;
    unsigned char _index;

    void next()
    {
        const std::size_t ch_ = *_it;

        _count = len(ch_);
        _index = 0;

        switch (_count)
        {
        case 1:
            _bytes[0] = static_cast<char>(ch_);
            break;
        case 2:
            _bytes[0] = static_cast<char>((ch_ >> 6) | 0xc0);
            _bytes[1] = (ch_ & 0x3f) | 0x80;
            break;
        case 3:
            _bytes[0] = static_cast<char>((ch_ >> 12) | 0xe0);
            _bytes[1] = ((ch_ >> 6) & 0x3f) | 0x80;
            _bytes[2] = (ch_ & 0x3f) | 0x80;
            break;
        case 4:
            _bytes[0] = static_cast<char>((ch_ >> 18) | 0xf0);
            _bytes[1] = ((ch_ >> 12) & 0x3f) | 0x80;
            _bytes[2] = ((ch_ >> 6) & 0x3f) | 0x80;
            _bytes[3] = (ch_ & 0x3f) | 0x80;
            break;
        }
    }

    char len(const std::size_t ch_) const
    {
        return ch_ < 0x80 ? 1 :
            ch_ < 0x800 ? 2 :
            ch_ < 0x10000 ? 3 :
            4;
    }
};

template<typename char_iterator, typename char_type>
class basic_utf16_in_iterator :
    public std::iterator<std::input_iterator_tag, char_type>
{
public:
    using value_type = char_type;
    using difference_type =
        typename std::iterator_traits<char_iterator>::difference_type;
    using iterator_category = std::forward_iterator_tag;

    basic_utf16_in_iterator() :
        _it(char_iterator()),
        _end(char_iterator()),
        _char(0)
    {
    }

    explicit basic_utf16_in_iterator(const char_iterator &it_,
        const char_iterator &end_) :
        _it(it_),
        _end(it_),
        _char(0)
    {
        if (it_ != end_)
        {
            next();
        }
    }

    char_type operator *() const
    {
        return _char;
    }

    bool operator ==(const basic_utf16_in_iterator &rhs_) const
    {
        return _it == rhs_._it;
    }

    bool operator !=(const basic_utf16_in_iterator &rhs_) const
    {
        return _it != rhs_._it;
    }

    basic_utf16_in_iterator &operator ++()
    {
        _it = _end;
        next();
        return *this;
    }

    basic_utf16_in_iterator operator ++(int)
    {
        basic_utf16_in_iterator temp_ = *this;

        _it = _end;
        next();
        return temp_;
    }

    basic_utf16_in_iterator operator +(const std::size_t count_) const
    {
        basic_utf16_in_iterator temp_ = *this;

        for (std::size_t i_ = 0; i_ < count_; ++i_)
        {
            ++temp_;
        }

        return temp_;
    }

    basic_utf16_in_iterator operator -(const std::size_t count_) const
    {
        basic_utf16_in_iterator temp_ = *this;

        for (std::size_t i_ = 0; i_ < count_; ++i_)
        {
            temp_._end = temp_._it;
            --temp_._it;

            if (*temp_._it >= 0xdc00 && *temp_._it <= 0xdfff) --temp_._it;
        }

        temp_.next();
        return temp_;
    }

private:
    char_iterator _it;
    char_iterator _end;
    char_type _char;

    void next()
    {
        char_type ch_ = *_it & 0xffff;

        _end = _it;

        if (ch_ >= 0xd800 && ch_ <= 0xdbff)
        {
            const char_type surrogate_ = *++_end & 0xffff;

            ch_ = (((ch_ - 0xd800) << 10) | (surrogate_ - 0xdc00)) + 0x10000;
        }

        _char = ch_;
        ++_end;
    }
};

template<typename char_iterator>
class basic_utf16_out_iterator :
    public std::iterator<std::input_iterator_tag, wchar_t>
{
public:
    using value_type = wchar_t;
    using difference_type =
        typename std::iterator_traits<char_iterator>::difference_type;
    using iterator_category = std::forward_iterator_tag;

    basic_utf16_out_iterator() :
        _count(0),
        _index(0)
    {
    }

    explicit basic_utf16_out_iterator(const char_iterator &it_,
        const char_iterator &end_) :
        _it(it_),
        _count(0),
        _index(0)
    {
        if (it_ != end_)
        {
            next();
        }
    }

    wchar_t operator *() const
    {
        return _chars[_index];
    }

    bool operator ==(const basic_utf16_out_iterator &rhs_) const
    {
        return _it == rhs_._it;
    }

    bool operator !=(const basic_utf16_out_iterator &rhs_) const
    {
        return _it != rhs_._it;
    }

    basic_utf16_out_iterator &operator ++()
    {
        ++_index;

        if (_index >= _count)
        {
            ++_it;
            next();
        }

        return *this;
    }

    basic_utf16_out_iterator operator ++(int)
    {
        basic_utf16_out_iterator temp_ = *this;

        ++_index;

        if (_index >= _count)
        {
            ++_it;
            next();
        }

        return temp_;
    }

private:
    char_iterator _it;
    wchar_t _chars[2];
    unsigned char _count;
    unsigned char _index;

    void next()
    {
        const std::size_t ch_ = *_it;

        _count = len(ch_);
        _index = 0;

        switch (_count)
        {
        case 1:
            _chars[0] = static_cast<wchar_t>(ch_);
            break;
        case 2:
            _chars[0] = static_cast<wchar_t>((ch_ >> 10) + 0xdc00u -
                (0x10000 >> 10));
            _chars[1] = static_cast<wchar_t>((ch_ & 0x3ff) + 0xdc00u);
            break;
        }
    }

    char len(const std::size_t ch_) const
    {
        return ch_ > 0xffff ? 2 : 1;
    }
};
}

#endif