text_cursor.hpp

// Copyright Take Vos 2022.
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE_1_0.txt or copy at https://www.boost.org/LICENSE_1_0.txt)
 
#pragma once
 
#include "../utility/module.hpp"
#include "../unicode/module.hpp"
#include <tuple>
#include <cstdlib>
#include <algorithm>
 
namespace hi::inline v1 {

class text_cursor {
public:
    constexpr text_cursor() noexcept = default;
    constexpr text_cursor(text_cursor const&) noexcept = default;
    constexpr text_cursor(text_cursor&&) noexcept = default;
    constexpr text_cursor& operator=(text_cursor const&) noexcept = default;
    constexpr text_cursor& operator=(text_cursor&&) noexcept = default;
    [[nodiscard]] constexpr friend bool operator==(text_cursor const&, text_cursor const&) = default;
    [[nodiscard]] constexpr friend auto operator<=>(text_cursor const&, text_cursor const&) = default;

    constexpr text_cursor& resize(size_t size) & noexcept
    {
        inplace_min(_value, max_value(size));
        return *this;
    }
 
    constexpr text_cursor resize(size_t size) && noexcept
    {
        inplace_min(_value, max_value(size));
        return *this;
    }
 

    constexpr text_cursor(size_t index, bool after) noexcept
    {
        _value = (index << 1) | static_cast<size_t>(after);
    }

    [[nodiscard]] constexpr text_cursor neighbor(size_t size) const noexcept
    {
        auto r = before() ? text_cursor{index() - 1, true} : text_cursor{index() + 1, false};
        return r.resize(size);
    }
 
    [[nodiscard]] constexpr text_cursor after_neighbor(size_t size) const noexcept
    {
        return before() ? neighbor(size) : *this;
    }
 
    [[nodiscard]] constexpr text_cursor before_neighbor(size_t size) const noexcept
    {
        return after() ? neighbor(size) : *this;
    }
 
    [[nodiscard]] constexpr bool start_of_text() const noexcept
    {
        return _value == 0;
    }
 
    [[nodiscard]] constexpr bool end_of_text(size_t size) const noexcept
    {
        return _value >= max_value(size);
    }
 
    [[nodiscard]] constexpr size_t index() const noexcept
    {
        return _value >> 1;
    }
 
    [[nodiscard]] constexpr bool after() const noexcept
    {
        return to_bool(_value & 1);
    }
 
    [[nodiscard]] constexpr bool before() const noexcept
    {
        return not after();
    }
 
private:
    [[nodiscard]] constexpr static size_t max_value(size_t size) noexcept
    {
        if (size) {
            size <<= 1;
            --size;
        }
        return size;
    }

    size_t _value = 0;
};
 
} // namespace hi::inline v1