text_widget.hpp

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// Copyright Take Vos 2021-2022.
// 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 "widget.hpp"
#include "text_delegate.hpp"
#include "../GUI/GUI.hpp"
#include "../text/text.hpp"
#include "../geometry/geometry.hpp"
#include "../l10n/l10n.hpp"
#include "../container/container.hpp"
#include "../observer/observer.hpp"
#include "../macros.hpp"
#include <memory>
#include <string>
#include <array>
#include <optional>
#include <future>
#include <limits>
#include <chrono>
 
hi_export_module(hikogui.widgets.text_widget);
 
hi_export namespace hi {
inline namespace v1 {
 
template<typename Context>
concept text_widget_attribute = forward_of<Context, observer<hi::alignment>>;

class text_widget : public widget {
public:
    using super = widget;
    using delegate_type = text_delegate;
 
    std::shared_ptr<delegate_type> delegate;

    observer<alignment> alignment = hi::alignment::top_flush();
 
    ~text_widget()
    {
        hi_assert_not_null(delegate);
        delegate->deinit(*this);
    }

    text_widget(std::shared_ptr<delegate_type> delegate) noexcept :
        super(), delegate(std::move(delegate))
    {
        set_mode(widget_mode::select);
 
        hi_assert_not_null(this->delegate);
        _delegate_cbt = this->delegate->subscribe([&] {
            // On every text edit, immediately/synchronously update the shaped text.
            // This is needed for handling multiple edit commands before the next frame update.
            if (_layout) {
                auto new_layout = _layout;
                auto const old_constraints = _constraints_cache;
 
                // Constrain and layout according to the old layout.
                auto const new_constraints = update_constraints();
                new_layout.shape.rectangle = aarectangle{
                    new_layout.shape.x(),
                    new_layout.shape.y(),
                    std::max(new_layout.shape.width(), new_constraints.minimum.width()),
                    std::max(new_layout.shape.height(), new_constraints.minimum.height())};
                set_layout(new_layout);
 
                if (new_constraints != old_constraints) {
                    // The constraints have changed, properly constrain and layout on the next frame.
                    ++global_counter<"text_widget:delegate:constrain">;
                    request_scroll();
                    process_event({gui_event_type::window_reconstrain});
                }
            } else {
                // The layout is incomplete, properly constrain and layout on the next frame.
                ++global_counter<"text_widget:delegate:constrain">;
                request_scroll();
                process_event({gui_event_type::window_reconstrain});
            }
        });
 
        _cursor_state_cbt = _cursor_state.subscribe([&](auto...) {
            ++global_counter<"text_widget:cursor_state:redraw">;
            request_redraw();
        });
 
        // If the text_widget is used as a label the blink_cursor() co-routine
        // is only waiting on `model` and `focus`, so this is cheap.
        _blink_cursor = blink_cursor();
 
        this->delegate->init(*this);
    }
 
    template<text_widget_attribute... Attributes>
    text_widget(
        std::shared_ptr<delegate_type> delegate,
        Attributes&&... attributes) noexcept :
        text_widget(std::move(delegate))
    {
        set_attributes(std::forward<Attributes>(attributes)...);
    }

    template<incompatible_with<std::shared_ptr<delegate_type>> Text, text_widget_attribute... Attributes>
    text_widget(
        Text&& text,
        Attributes&&... attributes) noexcept requires requires { make_default_text_delegate(std::forward<Text>(text)); }
        : text_widget(make_default_text_delegate(std::forward<Text>(text)), std::forward<Attributes>(attributes)...)
    {
    }

    [[nodiscard]] box_constraints update_constraints() noexcept override
    {
        _layout = {};
 
        // Read the latest text from the delegate.
        hi_assert_not_null(delegate);
        _text_cache = delegate->read(*this);
 
        // Make sure that the current selection fits the new text.
        _selection.resize(_text_cache.size());
 
        // Create a new text_shaper with the new text.
        auto alignment_ = os_settings::left_to_right() ? *alignment : mirror(*alignment);
 
        _shaped_text = text_shaper{_text_cache, theme().text_style_set(), style.pixel_density(), alignment_, os_settings::left_to_right()};
 
        auto const shaped_text_rectangle = ceil(_shaped_text.bounding_rectangle(std::numeric_limits<float>::infinity()));
        auto const shaped_text_size = shaped_text_rectangle.size();
 
        if (mode() == widget_mode::partial) {
            // In line-edit mode the text should not wrap.
            return _constraints_cache = {
                       shaped_text_size, shaped_text_size, shaped_text_size, _shaped_text.resolved_alignment(), theme().margin()};
 
        } else {
            // Allow the text to be 550.0f pixels wide.
            auto const preferred_shaped_text_rectangle = ceil(_shaped_text.bounding_rectangle(550.0f));
            auto const preferred_shaped_text_size = preferred_shaped_text_rectangle.size();
 
            auto const height = std::max(shaped_text_size.height(), preferred_shaped_text_size.height());
            return _constraints_cache = {
                       extent2{preferred_shaped_text_size.width(), height},
                       extent2{preferred_shaped_text_size.width(), height},
                       extent2{shaped_text_size.width(), height},
                       _shaped_text.resolved_alignment(),
                       theme().margin()};
        }
    }
 
    void set_layout(widget_layout const& context) noexcept override
    {
        if (compare_store(_layout, context)) {
            hi_assert(context.shape.baseline);
 
            _shaped_text.layout(context.rectangle(), *context.shape.baseline, context.sub_pixel_size);
        }
    }
 
    void draw(draw_context const& context) noexcept override
    {
        using namespace std::literals::chrono_literals;
 
        // After potential reconstrain and relayout, updating the shaped-text, ask the parent window to scroll if needed.
        if (std::exchange(_request_scroll, false)) {
            scroll_to_show_selection();
        }
 
        if (_last_drag_mouse_event) {
            if (_last_drag_mouse_event_next_repeat == utc_nanoseconds{}) {
                _last_drag_mouse_event_next_repeat = context.display_time_point + os_settings::keyboard_repeat_delay();
 
            } else if (context.display_time_point >= _last_drag_mouse_event_next_repeat) {
                _last_drag_mouse_event_next_repeat = context.display_time_point + os_settings::keyboard_repeat_interval();
 
                // The last drag mouse event was stored in window coordinate to compensate for scrolling, translate it
                // back to local coordinates before handling the mouse event again.
                auto new_mouse_event = _last_drag_mouse_event;
                new_mouse_event.mouse().position = _layout.from_window * _last_drag_mouse_event.mouse().position;
 
                // When mouse is dragging a selection, start continues redraw and scroll parent views to display the selection.
                text_widget::handle_event(new_mouse_event);
            }
            scroll_to_show_selection();
            ++global_counter<"text_widget:mouse_drag:redraw">;
            request_redraw();
        }
 
        if (mode() > widget_mode::invisible and overlaps(context, layout())) {
            context.draw_text(layout(), _shaped_text);
 
            context.draw_text_selection(layout(), _shaped_text, _selection, theme().text_select_color());
 
            if (*_cursor_state == cursor_state_type::on or *_cursor_state == cursor_state_type::busy) {
                context.draw_text_cursors(
                    layout(),
                    _shaped_text,
                    _selection.cursor(),
                    _overwrite_mode,
                    to_bool(_has_dead_character),
                    theme().primary_cursor_color(),
                    theme().secondary_cursor_color());
            }
        }
    }
 
    bool handle_event(gui_event const& event) noexcept override
    {
        hi_axiom(loop::main().on_thread());
 
        switch (event.type()) {
            using enum gui_event_type;
            using enum widget_mode;
 
        case gui_widget_next:
        case gui_widget_prev:
        case keyboard_exit:
            // When the next widget is selected due to pressing the Tab key the text should be committed.
            // The `text_widget` does not handle gui_activate, so it will be forwarded to parent widgets,
            // such as `text_field_widget` which does.
            process_event(gui_event_type::gui_activate);
            return super::handle_event(event);
 
        case keyboard_grapheme:
            if (mode() >= partial) {
                reset_state("BDX");
                add_character(event.grapheme(), add_type::append);
                return true;
            }
            break;
 
        case keyboard_partial_grapheme:
            if (mode() >= partial) {
                reset_state("BDX");
                add_character(event.grapheme(), add_type::dead);
                return true;
            }
            break;
 
        case text_mode_insert:
            if (mode() >= partial) {
                reset_state("BDX");
                _overwrite_mode = not _overwrite_mode;
                fix_cursor_position();
                return true;
            }
            break;
 
        case text_edit_paste:
            if (mode() >= partial) {
                reset_state("BDX");
                auto tmp = event.clipboard_data();
                // Replace all paragraph separators with white-space.
                std::replace(tmp.begin(), tmp.end(), grapheme{unicode_PS}, grapheme{' '});
                replace_selection(tmp);
                return true;
 
            } else if (mode() >= enabled) {
                reset_state("BDX");
                replace_selection(event.clipboard_data());
                return true;
            }
            break;
 
        case text_edit_copy:
            if (mode() >= select) {
                reset_state("BDX");
                if (auto const selected_text_ = selected_text(); not selected_text_.empty()) {
                    process_event(gui_event::make_clipboard_event(gui_event_type::window_set_clipboard, selected_text_));
                }
                return true;
            }
            break;
 
        case text_edit_cut:
            if (mode() >= select) {
                reset_state("BDX");
                process_event(gui_event::make_clipboard_event(gui_event_type::window_set_clipboard, selected_text()));
                if (mode() >= partial) {
                    replace_selection(gstring{});
                }
                return true;
            }
            break;
 
        case text_undo:
            if (mode() >= partial) {
                reset_state("BDX");
                undo();
                return true;
            }
            break;
 
        case text_redo:
            if (mode() >= partial) {
                reset_state("BDX");
                redo();
                return true;
            }
            break;
 
        case text_insert_line:
            if (mode() >= enabled) {
                reset_state("BDX");
                add_character(grapheme{unicode_PS}, add_type::append);
                return true;
            }
            break;
 
        case text_insert_line_up:
            if (mode() >= enabled) {
                reset_state("BDX");
                _selection = _shaped_text.move_begin_paragraph(_selection.cursor());
                add_character(grapheme{unicode_PS}, add_type::insert);
                return true;
            }
            break;
 
        case text_insert_line_down:
            if (mode() >= enabled) {
                reset_state("BDX");
                _selection = _shaped_text.move_end_paragraph(_selection.cursor());
                add_character(grapheme{unicode_PS}, add_type::insert);
                return true;
            }
            break;
 
        case text_delete_char_next:
            if (mode() >= partial) {
                reset_state("BDX");
                delete_character_next();
                return true;
            }
            break;
 
        case text_delete_char_prev:
            if (mode() >= partial) {
                reset_state("BDX");
                delete_character_prev();
                return true;
            }
            break;
 
        case text_delete_word_next:
            if (mode() >= partial) {
                reset_state("BDX");
                delete_word_next();
                return true;
            }
            break;
 
        case text_delete_word_prev:
            if (mode() >= partial) {
                reset_state("BDX");
                delete_word_prev();
                return true;
            }
            break;
 
        case text_cursor_left_char:
            if (mode() >= partial) {
                reset_state("BDX");
                _selection = _shaped_text.move_left_char(_selection.cursor(), _overwrite_mode);
                request_scroll();
                return true;
            }
            break;
 
        case text_cursor_right_char:
            if (mode() >= partial) {
                reset_state("BDX");
                _selection = _shaped_text.move_right_char(_selection.cursor(), _overwrite_mode);
                request_scroll();
                return true;
            }
            break;
 
        case text_cursor_down_char:
            if (mode() >= partial) {
                reset_state("BD");
                _selection = _shaped_text.move_down_char(_selection.cursor(), _vertical_movement_x);
                request_scroll();
                return true;
            }
            break;
 
        case text_cursor_up_char:
            if (mode() >= partial) {
                reset_state("BD");
                _selection = _shaped_text.move_up_char(_selection.cursor(), _vertical_movement_x);
                request_scroll();
                return true;
            }
            break;
 
        case text_cursor_left_word:
            if (mode() >= partial) {
                reset_state("BDX");
                _selection = _shaped_text.move_left_word(_selection.cursor(), _overwrite_mode);
                request_scroll();
                return true;
            }
            break;
 
        case text_cursor_right_word:
            if (mode() >= partial) {
                reset_state("BDX");
                _selection = _shaped_text.move_right_word(_selection.cursor(), _overwrite_mode);
                request_scroll();
                return true;
            }
            break;
 
        case text_cursor_begin_line:
            if (mode() >= partial) {
                reset_state("BDX");
                _selection = _shaped_text.move_begin_line(_selection.cursor());
                request_scroll();
                return true;
            }
            break;
 
        case text_cursor_end_line:
            if (mode() >= partial) {
                reset_state("BDX");
                _selection = _shaped_text.move_end_line(_selection.cursor());
                request_scroll();
                return true;
            }
            break;
 
        case text_cursor_begin_sentence:
            if (mode() >= partial) {
                reset_state("BDX");
                _selection = _shaped_text.move_begin_sentence(_selection.cursor());
                request_scroll();
                return true;
            }
            break;
 
        case text_cursor_end_sentence:
            if (mode() >= partial) {
                reset_state("BDX");
                _selection = _shaped_text.move_end_sentence(_selection.cursor());
                request_scroll();
                return true;
            }
            break;
 
        case text_cursor_begin_document:
            if (mode() >= partial) {
                reset_state("BDX");
                _selection = _shaped_text.move_begin_document(_selection.cursor());
                request_scroll();
                return true;
            }
            break;
 
        case text_cursor_end_document:
            if (mode() >= partial) {
                reset_state("BDX");
                _selection = _shaped_text.move_end_document(_selection.cursor());
                request_scroll();
                return true;
            }
            break;
 
        case gui_cancel:
            if (mode() >= select) {
                reset_state("BDX");
                _selection.clear_selection(_shaped_text.size());
                return true;
            }
            break;
 
        case text_select_left_char:
            if (mode() >= partial) {
                reset_state("BDX");
                _selection.drag_selection(_shaped_text.move_left_char(_selection.cursor(), false));
                request_scroll();
                return true;
            }
            break;
 
        case text_select_right_char:
            if (mode() >= partial) {
                reset_state("BDX");
                _selection.drag_selection(_shaped_text.move_right_char(_selection.cursor(), false));
                request_scroll();
                return true;
            }
            break;
 
        case text_select_down_char:
            if (mode() >= partial) {
                reset_state("BD");
                _selection.drag_selection(_shaped_text.move_down_char(_selection.cursor(), _vertical_movement_x));
                request_scroll();
                return true;
            }
            break;
 
        case text_select_up_char:
            if (mode() >= partial) {
                reset_state("BD");
                _selection.drag_selection(_shaped_text.move_up_char(_selection.cursor(), _vertical_movement_x));
                request_scroll();
                return true;
            }
            break;
 
        case text_select_left_word:
            if (mode() >= partial) {
                reset_state("BDX");
                _selection.drag_selection(_shaped_text.move_left_word(_selection.cursor(), false));
                request_scroll();
                return true;
            }
            break;
 
        case text_select_right_word:
            if (mode() >= partial) {
                reset_state("BDX");
                _selection.drag_selection(_shaped_text.move_right_word(_selection.cursor(), false));
                request_scroll();
                return true;
            }
            break;
 
        case text_select_begin_line:
            if (mode() >= partial) {
                reset_state("BDX");
                _selection.drag_selection(_shaped_text.move_begin_line(_selection.cursor()));
                request_scroll();
                return true;
            }
            break;
 
        case text_select_end_line:
            if (mode() >= partial) {
                reset_state("BDX");
                _selection.drag_selection(_shaped_text.move_end_line(_selection.cursor()));
                request_scroll();
                return true;
            }
            break;
 
        case text_select_begin_sentence:
            if (mode() >= partial) {
                reset_state("BDX");
                _selection.drag_selection(_shaped_text.move_begin_sentence(_selection.cursor()));
                request_scroll();
                return true;
            }
            break;
 
        case text_select_end_sentence:
            if (mode() >= partial) {
                reset_state("BDX");
                _selection.drag_selection(_shaped_text.move_end_sentence(_selection.cursor()));
                request_scroll();
                return true;
            }
            break;
 
        case text_select_begin_document:
            if (mode() >= partial) {
                reset_state("BDX");
                _selection.drag_selection(_shaped_text.move_begin_document(_selection.cursor()));
                request_scroll();
                return true;
            }
            break;
 
        case text_select_end_document:
            if (mode() >= partial) {
                reset_state("BDX");
                _selection.drag_selection(_shaped_text.move_end_document(_selection.cursor()));
                request_scroll();
                return true;
            }
            break;
 
        case text_select_document:
            if (mode() >= partial) {
                reset_state("BDX");
                _selection = _shaped_text.move_begin_document(_selection.cursor());
                _selection.drag_selection(_shaped_text.move_end_document(_selection.cursor()));
                request_scroll();
                return true;
            }
            break;
 
        case mouse_up:
            if (mode() >= select) {
                // Stop the continues redrawing during dragging.
                // Also reset the time, so on drag-start it will initialize the time, which will
                // cause a smooth startup of repeating.
                _last_drag_mouse_event = {};
                _last_drag_mouse_event_next_repeat = {};
                return true;
            }
            break;
 
        case mouse_down:
            if (mode() >= select) {
                auto const cursor = _shaped_text.get_nearest_cursor(event.mouse().position);
                switch (event.mouse().click_count) {
                case 1:
                    reset_state("BDX");
                    _selection = cursor;
                    break;
                case 2:
                    reset_state("BDX");
                    _selection.start_selection(cursor, _shaped_text.select_word(cursor));
                    break;
                case 3:
                    reset_state("BDX");
                    _selection.start_selection(cursor, _shaped_text.select_sentence(cursor));
                    break;
                case 4:
                    reset_state("BDX");
                    _selection.start_selection(cursor, _shaped_text.select_paragraph(cursor));
                    break;
                case 5:
                    reset_state("BDX");
                    _selection.start_selection(cursor, _shaped_text.select_document(cursor));
                    break;
                default:;
                }
 
                ++global_counter<"text_widget:mouse_down:relayout">;
                process_event({gui_event_type::window_relayout});
                request_scroll();
                return true;
            }
            break;
 
        case mouse_drag:
            if (mode() >= select) {
                auto const cursor = _shaped_text.get_nearest_cursor(event.mouse().position);
                switch (event.mouse().click_count) {
                case 1:
                    reset_state("BDX");
                    _selection.drag_selection(cursor);
                    break;
                case 2:
                    reset_state("BDX");
                    _selection.drag_selection(cursor, _shaped_text.select_word(cursor));
                    break;
                case 3:
                    reset_state("BDX");
                    _selection.drag_selection(cursor, _shaped_text.select_sentence(cursor));
                    break;
                case 4:
                    reset_state("BDX");
                    _selection.drag_selection(cursor, _shaped_text.select_paragraph(cursor));
                    break;
                default:;
                }
 
                // Drag events must be repeated, so that dragging is continues when it causes scrolling.
                // Normally mouse positions are kept in the local coordinate system, but scrolling
                // causes this coordinate system to shift, so translate it to the window coordinate system here.
                _last_drag_mouse_event = event;
                _last_drag_mouse_event.mouse().position = _layout.to_window * event.mouse().position;
                ++global_counter<"text_widget:mouse_drag:redraw">;
                request_redraw();
                return true;
            }
            break;
 
        default:;
        }
 
        return super::handle_event(event);
    }
 
    hitbox hitbox_test(point2 position) const noexcept override
    {
        hi_axiom(loop::main().on_thread());
 
        if (layout().contains(position)) {
            if (mode() >= widget_mode::partial) {
                return hitbox{id, _layout.elevation, hitbox_type::text_edit};
 
            } else if (mode() >= widget_mode::select) {
                return hitbox{id, _layout.elevation, hitbox_type::_default};
 
            } else {
                return hitbox{};
            }
        } else {
            return hitbox{};
        }
    }
 
    [[nodiscard]] bool accepts_keyboard_focus(keyboard_focus_group group) const noexcept override
    {
        if (mode() >= widget_mode::partial) {
            return to_bool(group & keyboard_focus_group::normal);
        } else if (mode() >= widget_mode::select) {
            return to_bool(group & keyboard_focus_group::mouse);
        } else {
            return false;
        }
    }
private:
    enum class add_type { append, insert, dead };
 
    struct undo_type {
        gstring text;
        text_selection selection;
    };
 
    enum class cursor_state_type { off, on, busy, none };
 
    gstring _text_cache;
    text_shaper _shaped_text;
 
    mutable box_constraints _constraints_cache;
 
    text_selection _selection;
 
    scoped_task<> _blink_cursor;
 
    observer<cursor_state_type> _cursor_state = cursor_state_type::none;

    bool _request_scroll = false;

    gui_event _last_drag_mouse_event = {};

    utc_nanoseconds _last_drag_mouse_event_next_repeat = {};

    float _vertical_movement_x = std::numeric_limits<float>::quiet_NaN();
 
    bool _overwrite_mode = false;

    std::optional<grapheme> _has_dead_character = std::nullopt;
 
    undo_stack<undo_type> _undo_stack = {1000};
 
    callback<void()> _delegate_cbt;
    callback<void(cursor_state_type)> _cursor_state_cbt;
 
    void set_attributes() noexcept {}
 
    template<text_widget_attribute First, text_widget_attribute... Rest>
    void set_attributes(First&& first, Rest&&... rest) noexcept
    {
        if constexpr (forward_of<First, observer<hi::alignment>>) {
            alignment = std::forward<First>(first);
        } else {
            hi_static_no_default();
        }
 
        set_attributes(std::forward<Rest>(rest)...);
    }

    void scroll_to_show_selection() noexcept
    {
        if (mode() > widget_mode::invisible and focus()) {
            auto const cursor = _selection.cursor();
            auto const char_it = _shaped_text.begin() + cursor.index();
            if (char_it < _shaped_text.end()) {
                scroll_to_show(char_it->rectangle);
            }
        }
    }
 
    void request_scroll() noexcept
    {
        // At a minimum we need to request a redraw so that
        // `scroll_to_show_selection()` is called on the next frame.
        _request_scroll = true;
        ++global_counter<"text_widget:request_scroll:redraw">;
        request_redraw();
    }

    void reset_state(char const* states) noexcept
    {
        hi_assert_not_null(states);
 
        while (*states != 0) {
            switch (*states) {
            case 'D':
                delete_dead_character();
                break;
            case 'X':
                _vertical_movement_x = std::numeric_limits<float>::quiet_NaN();
                break;
            case 'B':
                if (*_cursor_state == cursor_state_type::on or *_cursor_state == cursor_state_type::off) {
                    _cursor_state = cursor_state_type::busy;
                }
                break;
            default:
                hi_no_default();
            }
            ++states;
        }
    }
 
    [[nodiscard]] gstring_view selected_text() const noexcept
    {
        auto const[first, last] = _selection.selection_indices();
 
        return gstring_view{_text_cache}.substr(first, last - first);
    }
 
    void undo_push() noexcept
    {
        _undo_stack.emplace(_text_cache, _selection);
    }
 
    void undo() noexcept
    {
        if (_undo_stack.can_undo()) {
            auto const & [ text, selection ] = _undo_stack.undo(_text_cache, _selection);
 
            delegate->write(*this, text);
            _selection = selection;
        }
    }
 
    void redo() noexcept
    {
        if (_undo_stack.can_redo()) {
            auto const & [ text, selection ] = _undo_stack.redo();
 
            delegate->write(*this, text);
            _selection = selection;
        }
    }
 
    scoped_task<> blink_cursor() noexcept
    {
        while (true) {
            if (mode() >= widget_mode::partial and focus()) {
                switch (*_cursor_state) {
                case cursor_state_type::busy:
                    _cursor_state = cursor_state_type::on;
                    co_await when_any(os_settings::cursor_blink_delay(), state);
                    break;
 
                case cursor_state_type::on:
                    _cursor_state = cursor_state_type::off;
                    co_await when_any(os_settings::cursor_blink_interval() / 2, state);
                    break;
 
                case cursor_state_type::off:
                    _cursor_state = cursor_state_type::on;
                    co_await when_any(os_settings::cursor_blink_interval() / 2, state);
                    break;
 
                default:
                    _cursor_state = cursor_state_type::busy;
                }
 
            } else {
                _cursor_state = cursor_state_type::none;
                co_await state;
            }
        }
    }

    void fix_cursor_position() noexcept
    {
        auto const size = _text_cache.size();
        if (_overwrite_mode and _selection.empty() and _selection.cursor().after()) {
            _selection = _selection.cursor().before_neighbor(size);
        }
        _selection.resize(size);
    }

    void replace_selection(gstring const& replacement) noexcept
    {
        undo_push();
 
        auto const[first, last] = _selection.selection_indices();
 
        auto text = _text_cache;
        text.replace(first, last - first, replacement);
        delegate->write(*this, text);
 
        _selection = text_cursor{first + replacement.size() - 1, true};
        fix_cursor_position();
    }

    void add_character(grapheme c, add_type keyboard_mode) noexcept
    {
        auto const[start_selection, end_selection] = _selection.selection(_text_cache.size());
        auto original_grapheme = grapheme{char32_t{0xffff}};
 
        if (_selection.empty() and _overwrite_mode and start_selection.before()) {
            original_grapheme = _text_cache[start_selection.index()];
 
            auto const[first, last] = _shaped_text.select_char(start_selection);
            _selection.drag_selection(last);
        }
        replace_selection(gstring{c});
 
        if (keyboard_mode == add_type::insert) {
            // The character was inserted, put the cursor back where it was.
            _selection = start_selection;
 
        } else if (keyboard_mode == add_type::dead) {
            _selection = start_selection.before_neighbor(_text_cache.size());
            _has_dead_character = original_grapheme;
        }
    }
 
    void delete_dead_character() noexcept
    {
        if (_has_dead_character) {
            hi_assert(_selection.cursor().before());
            hi_assert_bounds(_selection.cursor().index(), _text_cache);
 
            if (_has_dead_character != U'\uffff') {
                auto text = _text_cache;
                text[_selection.cursor().index()] = *_has_dead_character;
                delegate->write(*this, text);
            } else {
                auto text = _text_cache;
                text.erase(_selection.cursor().index(), 1);
                delegate->write(*this, text);
            }
        }
        _has_dead_character = std::nullopt;
    }
 
    void delete_character_next() noexcept
    {
        if (_selection.empty()) {
            auto cursor = _selection.cursor();
            cursor = cursor.before_neighbor(_shaped_text.size());
 
            auto const[first, last] = _shaped_text.select_char(cursor);
            _selection.drag_selection(last);
        }
 
        return replace_selection(gstring{});
    }
 
    void delete_character_prev() noexcept
    {
        if (_selection.empty()) {
            auto cursor = _selection.cursor();
            cursor = cursor.after_neighbor(_shaped_text.size());
 
            auto const[first, last] = _shaped_text.select_char(cursor);
            _selection.drag_selection(first);
        }
 
        return replace_selection(gstring{});
    }
 
    void delete_word_next() noexcept
    {
        if (_selection.empty()) {
            auto cursor = _selection.cursor();
            cursor = cursor.before_neighbor(_shaped_text.size());
 
            auto const[first, last] = _shaped_text.select_word(cursor);
            _selection.drag_selection(last);
        }
 
        return replace_selection(gstring{});
    }
 
    void delete_word_prev() noexcept
    {
        if (_selection.empty()) {
            auto cursor = _selection.cursor();
            cursor = cursor.after_neighbor(_shaped_text.size());
 
            auto const[first, last] = _shaped_text.select_word(cursor);
            _selection.drag_selection(first);
        }
 
        return replace_selection(gstring{});
    }
};
 
} // namespace v1
} // namespace hi::v1