ladybird/Libraries/LibLine/Editor.cpp

/*
 * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice, this
 *    list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "Editor.h"
#include <AK/JsonObject.h>
#include <AK/StringBuilder.h>
#include <AK/Utf32View.h>
#include <AK/Utf8View.h>
#include <LibCore/Event.h>
#include <LibCore/EventLoop.h>
#include <LibCore/Notifier.h>
#include <ctype.h>
#include <stdio.h>
#include <sys/ioctl.h>
#include <sys/select.h>
#include <sys/time.h>
#include <unistd.h>

// #define SUGGESTIONS_DEBUG

namespace {
u32 ctrl(char c) { return c & 0x3f; }
}

namespace Line {

Editor::Editor(Configuration configuration)
    : m_configuration(move(configuration))
{
    m_always_refresh = configuration.refresh_behaviour == Configuration::RefreshBehaviour::Eager;
    m_pending_chars = ByteBuffer::create_uninitialized(0);
    get_terminal_size();
    m_suggestion_display = make<XtermSuggestionDisplay>(m_num_lines, m_num_columns);
}

Editor::~Editor()
{
    if (m_initialized)
        restore();
}

void Editor::get_terminal_size()
{
    struct winsize ws;
    if (ioctl(STDOUT_FILENO, TIOCGWINSZ, &ws) < 0) {
        m_num_columns = 80;
        m_num_lines = 25;
    } else {
        m_num_columns = ws.ws_col;
        m_num_lines = ws.ws_row;
    }
}

void Editor::add_to_history(const String& line)
{
    if (line.is_empty())
        return;
    if ((m_history.size() + 1) > m_history_capacity)
        m_history.take_first();
    m_history.append(line);
}

void Editor::clear_line()
{
    for (size_t i = 0; i < m_cursor; ++i)
        fputc(0x8, stdout);
    fputs("\033[K", stdout);
    fflush(stdout);
    m_buffer.clear();
    m_cursor = 0;
    m_inline_search_cursor = m_cursor;
}

void Editor::insert(const Utf32View& string)
{
    for (size_t i = 0; i < string.length(); ++i)
        insert(string.codepoints()[i]);
}

void Editor::insert(const String& string)
{
    for (auto ch : Utf8View { string })
        insert(ch);
}

void Editor::insert(const u32 cp)
{
    StringBuilder builder;
    builder.append(Utf32View(&cp, 1));
    auto str = builder.build();
    m_pending_chars.append(str.characters(), str.length());

    readjust_anchored_styles(m_cursor, ModificationKind::Insertion);

    if (m_cursor == m_buffer.size()) {
        m_buffer.append(cp);
        m_cursor = m_buffer.size();
        m_inline_search_cursor = m_cursor;
        return;
    }

    m_buffer.insert(m_cursor, cp);
    ++m_chars_inserted_in_the_middle;
    ++m_cursor;
    m_inline_search_cursor = m_cursor;
}

void Editor::register_character_input_callback(char ch, Function<bool(Editor&)> callback)
{
    if (m_key_callbacks.contains(ch)) {
        dbg() << "Key callback registered twice for " << ch;
        ASSERT_NOT_REACHED();
    }
    m_key_callbacks.set(ch, make<KeyCallback>(move(callback)));
}

static size_t codepoint_length_in_utf8(u32 codepoint)
{
    if (codepoint <= 0x7f)
        return 1;
    if (codepoint <= 0x07ff)
        return 2;
    if (codepoint <= 0xffff)
        return 3;
    if (codepoint <= 0x10ffff)
        return 4;
    return 3;
}

// buffer [ 0 1 2 3 . . . A . . . B . . . M . . . N ]
//                        ^       ^       ^       ^
//                        |       |       |       +- end of buffer
//                        |       |       +- scan offset = M
//                        |       +- range end = M - B
//                        +- range start = M - A
// This method converts a byte range defined by [start_byte_offset, end_byte_offset] to a codepoint range [M - A, M - B] as shown in the diagram above.
// If `reverse' is true, A and B are before M, if not, A and B are after M.
Editor::CodepointRange Editor::byte_offset_range_to_codepoint_offset_range(size_t start_byte_offset, size_t end_byte_offset, size_t scan_codepoint_offset, bool reverse) const
{
    size_t byte_offset = 0;
    size_t codepoint_offset = scan_codepoint_offset + (reverse ? 1 : 0);
    CodepointRange range;

    for (;;) {
        if (!reverse) {
            if (codepoint_offset >= m_buffer.size())
                break;
        } else {
            if (codepoint_offset == 0)
                break;
        }

        if (byte_offset > end_byte_offset)
            break;

        if (byte_offset < start_byte_offset)
            ++range.start;

        if (byte_offset < end_byte_offset)
            ++range.end;

        byte_offset += codepoint_length_in_utf8(m_buffer[reverse ? --codepoint_offset : codepoint_offset++]);
    }

    return range;
}

void Editor::stylize(const Span& span, const Style& style)
{
    if (style.is_empty())
        return;

    auto start = span.beginning();
    auto end = span.end();

    if (span.mode() == Span::ByteOriented) {
        auto offsets = byte_offset_range_to_codepoint_offset_range(start, end, 0);

        start = offsets.start;
        end = offsets.end;
    }

    auto& spans_starting = style.is_anchored() ? m_anchored_spans_starting : m_spans_starting;
    auto& spans_ending = style.is_anchored() ? m_anchored_spans_ending : m_spans_ending;

    auto starting_map = spans_starting.get(start).value_or({});

    if (!starting_map.contains(end))
        m_refresh_needed = true;

    starting_map.set(end, style);

    spans_starting.set(start, starting_map);

    auto ending_map = spans_ending.get(end).value_or({});

    if (!ending_map.contains(start))
        m_refresh_needed = true;
    ending_map.set(start, style);

    spans_ending.set(end, ending_map);
}

void Editor::suggest(size_t invariant_offset, size_t static_offset, Span::Mode offset_mode) const
{
    auto internal_static_offset = static_offset;
    auto internal_invariant_offset = invariant_offset;
    if (offset_mode == Span::Mode::ByteOriented) {
        // FIXME: We're assuming that invariant_offset points to the end of the available data
        //        this is not necessarily true, but is true in most cases.
        auto offsets = byte_offset_range_to_codepoint_offset_range(internal_static_offset, internal_invariant_offset + internal_static_offset, m_cursor - 1, true);

        internal_static_offset = offsets.start;
        internal_invariant_offset = offsets.end - offsets.start;
    }
    m_suggestion_manager.set_suggestion_variants(internal_static_offset, internal_invariant_offset, 0);
}

void Editor::initialize()
{
    if (m_initialized)
        return;

    struct termios termios;
    tcgetattr(0, &termios);
    m_default_termios = termios; // grab a copy to restore
    if (m_was_resized)
        get_terminal_size();

    if (m_configuration.operation_mode == Configuration::Unset) {
        auto istty = isatty(STDIN_FILENO) && isatty(STDOUT_FILENO);
        if (!istty) {
            m_configuration.set(Configuration::NonInteractive);
        } else {
            auto* term = getenv("TERM");
            if (StringView { term }.starts_with("xterm"))
                m_configuration.set(Configuration::Full);
            else
                m_configuration.set(Configuration::NoEscapeSequences);
        }
    }

    // Because we use our own line discipline which includes echoing,
    // we disable ICANON and ECHO.
    if (m_configuration.operation_mode == Configuration::Full) {
        termios.c_lflag &= ~(ECHO | ICANON);
        tcsetattr(0, TCSANOW, &termios);
    }

    m_termios = termios;
    m_initialized = true;
}

auto Editor::get_line(const String& prompt) -> Result<String, Editor::Error>
{
    initialize();
    m_is_editing = true;

    if (m_configuration.operation_mode == Configuration::NoEscapeSequences || m_configuration.operation_mode == Configuration::NonInteractive) {
        // Do not use escape sequences, instead, use LibC's getline.
        size_t size = 0;
        char* line = nullptr;
        // Show the prompt only on interactive mode (NoEscapeSequences in this case).
        if (m_configuration.operation_mode != Configuration::NonInteractive)
            fputs(prompt.characters(), stderr);
        auto line_length = getline(&line, &size, stdin);
        // getline() returns -1 and sets errno=0 on EOF.
        if (line_length == -1) {
            if (line)
                free(line);
            if (errno == 0)
                return Error::Eof;

            return Error::ReadFailure;
        }
        restore();
        if (line) {
            String result { line, (size_t)line_length, Chomp };
            free(line);
            return result;
        }

        return Error::ReadFailure;
    }

    set_prompt(prompt);
    reset();
    set_origin();
    strip_styles(true);

    m_history_cursor = m_history.size();

    refresh_display();

    Core::EventLoop loop;

    m_notifier = Core::Notifier::construct(STDIN_FILENO, Core::Notifier::Read);
    add_child(*m_notifier);

    m_notifier->on_ready_to_read = [&] {
        if (m_was_interrupted)
            handle_interrupt_event();

        handle_read_event();

        if (m_always_refresh)
            m_refresh_needed = true;

        refresh_display();

        if (m_finish) {
            m_finish = false;
            reposition_cursor(true);
            printf("\n");
            fflush(stdout);
            auto string = line();
            m_buffer.clear();
            m_is_editing = false;
            restore();

            m_returned_line = string;

            m_notifier->set_event_mask(Core::Notifier::None);
            deferred_invoke([this](auto&) {
                remove_child(*m_notifier);
                m_notifier = nullptr;
                Core::EventLoop::current().quit(0);
            });
        }
    };

    loop.exec();

    return m_input_error.has_value() ? Result<String, Editor::Error> { m_input_error.value() } : Result<String, Editor::Error> { m_returned_line };
}

void Editor::save_to(JsonObject& object)
{
    Core::Object::save_to(object);
    object.set("is_searching", m_is_searching);
    object.set("is_editing", m_is_editing);
    object.set("cursor_offset", m_cursor);
    object.set("needs_refresh", m_refresh_needed);
    object.set("unprocessed_characters", m_incomplete_data.size());
    object.set("history_size", m_history.size());
    object.set("current_prompt", m_new_prompt);
    object.set("was_interrupted", m_was_interrupted);
    JsonObject display_area;
    display_area.set("top_left_row", m_origin_row);
    display_area.set("top_left_column", m_origin_column);
    display_area.set("line_count", num_lines());
    object.set("used_display_area", move(display_area));
}

void Editor::handle_interrupt_event()
{
    m_was_interrupted = false;

    if (!m_buffer.is_empty())
        printf("^C");

    m_buffer.clear();
    m_cursor = 0;

    if (on_interrupt_handled)
        on_interrupt_handled();

    m_refresh_needed = true;
    refresh_display();
}

void Editor::handle_read_event()
{
    char keybuf[16];
    ssize_t nread = 0;

    if (!m_incomplete_data.size())
        nread = read(0, keybuf, sizeof(keybuf));

    if (nread < 0) {
        if (errno == EINTR) {
            if (!m_was_interrupted) {
                if (m_was_resized)
                    return;

                finish();
                return;
            }

            handle_interrupt_event();
            return;
        }

        ScopedValueRollback errno_restorer(errno);
        perror("read failed");

        m_input_error = Error::ReadFailure;
        finish();
        return;
    }

    m_incomplete_data.append(keybuf, nread);
    nread = m_incomplete_data.size();

    if (nread == 0) {
        m_input_error = Error::Empty;
        finish();
        return;
    }

    auto reverse_tab = false;
    auto ctrl_held = false;

    // Discard starting bytes until they make sense as utf-8.
    size_t valid_bytes = 0;
    while (nread) {
        Utf8View { StringView { m_incomplete_data.data(), (size_t)nread } }.validate(valid_bytes);
        if (valid_bytes)
            break;
        m_incomplete_data.take_first();
        --nread;
    }

    Utf8View input_view { StringView { m_incomplete_data.data(), valid_bytes } };
    size_t consumed_codepoints = 0;

    enum Amount {
        Character,
        Word,
    };
    auto do_cursor_left = [&](Amount amount) {
        if (m_cursor > 0) {
            if (amount == Word) {
                auto skipped_at_least_one_character = false;
                for (;;) {
                    if (m_cursor == 0)
                        break;
                    if (skipped_at_least_one_character && isspace(m_buffer[m_cursor - 1])) // stop *after* a space, but only if it changes the position
                        break;
                    skipped_at_least_one_character = true;
                    --m_cursor;
                }
            } else {
                --m_cursor;
            }
        }
        m_inline_search_cursor = m_cursor;
    };
    auto do_cursor_right = [&](Amount amount) {
        if (m_cursor < m_buffer.size()) {
            if (amount == Word) {
                // Temporarily put a space at the end of our buffer,
                // doing this greatly simplifies the logic below.
                m_buffer.append(' ');
                for (;;) {
                    if (m_cursor >= m_buffer.size())
                        break;
                    if (isspace(m_buffer[++m_cursor]))
                        break;
                }
                m_buffer.take_last();
            } else {
                ++m_cursor;
            }
        }
        m_inline_search_cursor = m_cursor;
        m_search_offset = 0;
    };

    auto do_search_backwards = [&] {
        m_searching_backwards = true;
        auto inline_search_cursor = m_inline_search_cursor;
        StringBuilder builder;
        builder.append(Utf32View { m_buffer.data(), inline_search_cursor });
        String search_phrase = builder.to_string();
        if (search(search_phrase, true, true)) {
            ++m_search_offset;
        } else {
            insert(search_phrase);
        }
        m_inline_search_cursor = inline_search_cursor;
    };

    auto do_search_forwards = [&] {
        auto inline_search_cursor = m_inline_search_cursor;
        StringBuilder builder;
        builder.append(Utf32View { m_buffer.data(), inline_search_cursor });
        String search_phrase = builder.to_string();
        auto search_changed_directions = m_searching_backwards;
        m_searching_backwards = false;
        if (m_search_offset > 0) {
            m_search_offset -= 1 + search_changed_directions;
            if (!search(search_phrase, true, true)) {
                insert(search_phrase);
            }
        } else {
            m_search_offset = 0;
            m_cursor = 0;
            m_buffer.clear();
            insert(search_phrase);
            m_refresh_needed = true;
        }
        m_inline_search_cursor = inline_search_cursor;
    };

    auto do_backspace = [&] {
        if (m_is_searching) {
            return;
        }
        if (m_cursor == 0) {
            fputc('\a', stdout);
            fflush(stdout);
            return;
        }
        remove_at_index(m_cursor - 1);
        --m_cursor;
        m_inline_search_cursor = m_cursor;
        // We will have to redraw :(
        m_refresh_needed = true;
    };

    auto do_delete = [&] {
        if (m_cursor == m_buffer.size()) {
            fputc('\a', stdout);
            fflush(stdout);
            return;
        }
        remove_at_index(m_cursor);
        m_refresh_needed = true;
    };

    for (auto codepoint : input_view) {
        if (m_finish)
            break;

        ++consumed_codepoints;

        if (codepoint == 0)
            continue;

        switch (m_state) {
        case InputState::ExpectBracket:
            if (codepoint == '[') {
                m_state = InputState::ExpectFinal;
                continue;
            } else {
                m_state = InputState::Free;
                break;
            }
        case InputState::ExpectFinal:
            switch (codepoint) {
            case 'O': // mod_ctrl
                ctrl_held = true;
                continue;
            case 'A': // up
                do_search_backwards();
                m_state = InputState::Free;
                ctrl_held = false;
                continue;
            case 'B': // down
                do_search_forwards();
                m_state = InputState::Free;
                ctrl_held = false;
                continue;
            case 'D': // left
                do_cursor_left(ctrl_held ? Word : Character);
                m_state = InputState::Free;
                ctrl_held = false;
                continue;
            case 'C': // right
                do_cursor_right(ctrl_held ? Word : Character);
                m_state = InputState::Free;
                ctrl_held = false;
                continue;
            case 'H':
                m_cursor = 0;
                m_inline_search_cursor = m_cursor;
                m_search_offset = 0;
                m_state = InputState::Free;
                ctrl_held = false;
                continue;
            case 'F':
                m_cursor = m_buffer.size();
                m_state = InputState::Free;
                m_inline_search_cursor = m_cursor;
                m_search_offset = 0;
                ctrl_held = false;
                continue;
            case 'Z': // shift+tab
                reverse_tab = true;
                m_state = InputState::Free;
                ctrl_held = false;
                break;
            case '3':
                do_delete();
                m_search_offset = 0;
                m_state = InputState::ExpectTerminator;
                ctrl_held = false;
                continue;
            default:
                dbgprintf("LibLine: Unhandled final: %02x (%c)\r\n", codepoint, codepoint);
                m_state = InputState::Free;
                ctrl_held = false;
                continue;
            }
            break;
        case InputState::ExpectTerminator:
            m_state = InputState::Free;
            continue;
        case InputState::Free:
            if (codepoint == 27) {
                m_state = InputState::ExpectBracket;
                continue;
            }
            break;
        }

        auto cb = m_key_callbacks.get(codepoint);
        if (cb.has_value()) {
            if (!cb.value()->callback(*this)) {
                continue;
            }
        }

        // ^N
        if (codepoint == ctrl('N')) {
            do_search_forwards();
            continue;
        }
        // ^P
        if (codepoint == ctrl('P')) {
            do_search_backwards();
            continue;
        }

        m_search_offset = 0; // reset search offset on any key

        if (codepoint == '\t' || reverse_tab) {
            if (!on_tab_complete)
                continue;

            // Reverse tab can count as regular tab here.
            m_times_tab_pressed++;

            int token_start = m_cursor;

            // Ask for completions only on the first tab
            // and scan for the largest common prefix to display,
            // further tabs simply show the cached completions.
            if (m_times_tab_pressed == 1) {
                m_suggestion_manager.set_suggestions(on_tab_complete(*this));
                m_prompt_lines_at_suggestion_initiation = num_lines();
                if (m_suggestion_manager.count() == 0) {
                    // There are no suggestions, beep.
                    putchar('\a');
                    fflush(stdout);
                }
            }

            // Adjust already incremented / decremented index when switching tab direction.
            if (reverse_tab && m_tab_direction != TabDirection::Backward) {
                m_suggestion_manager.previous();
                m_suggestion_manager.previous();
                m_tab_direction = TabDirection::Backward;
            }
            if (!reverse_tab && m_tab_direction != TabDirection::Forward) {
                m_suggestion_manager.next();
                m_suggestion_manager.next();
                m_tab_direction = TabDirection::Forward;
            }
            reverse_tab = false;

            auto completion_mode = m_times_tab_pressed == 1 ? SuggestionManager::CompletePrefix : m_times_tab_pressed == 2 ? SuggestionManager::ShowSuggestions : SuggestionManager::CycleSuggestions;

            auto completion_result = m_suggestion_manager.attempt_completion(completion_mode, token_start);

            auto new_cursor = m_cursor + completion_result.new_cursor_offset;
            for (size_t i = completion_result.offset_region_to_remove.start; i < completion_result.offset_region_to_remove.end; ++i)
                remove_at_index(new_cursor);

            m_cursor = new_cursor;
            m_inline_search_cursor = new_cursor;
            m_refresh_needed = true;

            for (auto& view : completion_result.insert)
                insert(view);

            if (completion_result.style_to_apply.has_value()) {
                // Apply the style of the last suggestion.
                readjust_anchored_styles(m_suggestion_manager.current_suggestion().start_index, ModificationKind::ForcedOverlapRemoval);
                stylize({ m_suggestion_manager.current_suggestion().start_index, m_cursor, Span::Mode::CodepointOriented }, completion_result.style_to_apply.value());
            }

            switch (completion_result.new_completion_mode) {
            case SuggestionManager::DontComplete:
                m_times_tab_pressed = 0;
                break;
            case SuggestionManager::CompletePrefix:
                break;
            default:
                ++m_times_tab_pressed;
                break;
            }

            if (m_times_tab_pressed > 1) {
                if (m_suggestion_manager.count() > 0) {
                    if (m_suggestion_display->cleanup())
                        reposition_cursor();

                    m_suggestion_display->set_initial_prompt_lines(m_prompt_lines_at_suggestion_initiation);

                    m_suggestion_display->display(m_suggestion_manager);

                    m_origin_row = m_suggestion_display->origin_row();
                }
            }

            if (m_times_tab_pressed > 2) {
                if (m_tab_direction == TabDirection::Forward)
                    m_suggestion_manager.next();
                else
                    m_suggestion_manager.previous();
            }

            if (m_suggestion_manager.count() < 2) {
                // We have none, or just one suggestion,
                // we should just commit that and continue
                // after it, as if it were auto-completed.
                suggest(0, 0, Span::CodepointOriented);
                m_times_tab_pressed = 0;
                m_suggestion_manager.reset();
                m_suggestion_display->finish();
            }
            continue;
        }

        if (m_times_tab_pressed) {
            // Apply the style of the last suggestion.
            readjust_anchored_styles(m_suggestion_manager.current_suggestion().start_index, ModificationKind::ForcedOverlapRemoval);
            stylize({ m_suggestion_manager.current_suggestion().start_index, m_cursor, Span::Mode::CodepointOriented }, m_suggestion_manager.current_suggestion().style);
            // We probably have some suggestions drawn,
            // let's clean them up.
            if (m_suggestion_display->cleanup()) {
                reposition_cursor();
                m_refresh_needed = true;
            }
            m_suggestion_manager.reset();
            suggest(0, 0, Span::CodepointOriented);
            m_suggestion_display->finish();
        }
        m_times_tab_pressed = 0; // Safe to say if we get here, the user didn't press TAB

        if (codepoint == m_termios.c_cc[VWERASE]) {
            bool has_seen_nonspace = false;
            while (m_cursor > 0) {
                if (isspace(m_buffer[m_cursor - 1])) {
                    if (has_seen_nonspace)
                        break;
                } else {
                    has_seen_nonspace = true;
                }
                do_backspace();
            }
            continue;
        }
        if (codepoint == m_termios.c_cc[VKILL]) {
            for (size_t i = 0; i < m_cursor; ++i)
                remove_at_index(0);
            m_cursor = 0;
            m_refresh_needed = true;
            continue;
        }
        // Normally ^D. `stty eof \^n` can change it to ^N (or something else), but Serenity doesn't have `stty` yet.
        // Handle it before ctrl shortcuts below and only continue if the buffer is empty, so that the editing shortcuts can take effect else.
        if (codepoint == m_termios.c_cc[VEOF] && m_buffer.is_empty()) {
            printf("<EOF>\n");
            if (!m_always_refresh) {
                m_input_error = Error::Eof;
                finish();
            }
            continue;
        }
        // ^A
        if (codepoint == ctrl('A')) {
            m_cursor = 0;
            continue;
        }
        // ^B
        if (codepoint == ctrl('B')) {
            do_cursor_left(Character);
            continue;
        }
        // ^D
        if (codepoint == ctrl('D')) {
            do_delete();
            continue;
        }
        // ^E
        if (codepoint == ctrl('E')) {
            m_cursor = m_buffer.size();
            continue;
        }
        // ^F
        if (codepoint == ctrl('F')) {
            do_cursor_right(Character);
            continue;
        }
        // ^H: ctrl('H') == '\b'
        if (codepoint == '\b' || codepoint == m_termios.c_cc[VERASE]) {
            do_backspace();
            continue;
        }
        // ^L
        if (codepoint == ctrl('L')) {
            printf("\033[3J\033[H\033[2J"); // Clear screen.
            VT::move_absolute(1, 1);
            set_origin(1, 1);
            m_refresh_needed = true;
            continue;
        }
        // ^R
        if (codepoint == ctrl('R')) {
            if (m_is_searching) {
                // how did we get here?
                ASSERT_NOT_REACHED();
            } else {
                m_is_searching = true;
                m_search_offset = 0;
                m_pre_search_buffer.clear();
                for (auto codepoint : m_buffer)
                    m_pre_search_buffer.append(codepoint);
                m_pre_search_cursor = m_cursor;

                // Disable our own notifier so as to avoid interfering with the search editor.
                m_notifier->set_enabled(false);

                m_search_editor = Editor::construct(Configuration { Configuration::Eager, m_configuration.split_mechanism }); // Has anyone seen 'Inception'?
                add_child(*m_search_editor);

                m_search_editor->on_display_refresh = [this](Editor& search_editor) {
                    StringBuilder builder;
                    builder.append(Utf32View { search_editor.buffer().data(), search_editor.buffer().size() });
                    search(builder.build());
                    refresh_display();
                    return;
                };

                // Whenever the search editor gets a ^R, cycle between history entries.
                m_search_editor->register_character_input_callback(ctrl('R'), [this](Editor& search_editor) {
                    ++m_search_offset;
                    search_editor.m_refresh_needed = true;
                    return false; // Do not process this key event
                });

                // Whenever the search editor gets a backspace, cycle back between history entries
                // unless we're at the zeroth entry, in which case, allow the deletion.
                m_search_editor->register_character_input_callback(m_termios.c_cc[VERASE], [this](Editor& search_editor) {
                    if (m_search_offset > 0) {
                        --m_search_offset;
                        search_editor.m_refresh_needed = true;
                        return false; // Do not process this key event
                    }
                    return true;
                });

                // ^L - This is a source of issues, as the search editor refreshes first,
                // and we end up with the wrong order of prompts, so we will first refresh
                // ourselves, then refresh the search editor, and then tell him not to process
                // this event.
                m_search_editor->register_character_input_callback(ctrl('L'), [this](auto& search_editor) {
                    printf("\033[3J\033[H\033[2J"); // Clear screen.

                    // refresh our own prompt
                    set_origin(1, 1);
                    m_refresh_needed = true;
                    refresh_display();

                    // move the search prompt below ours
                    // and tell it to redraw itself
                    search_editor.set_origin(2, 1);
                    search_editor.m_refresh_needed = true;

                    return false;
                });

                // quit without clearing the current buffer
                m_search_editor->register_character_input_callback('\t', [this](Editor& search_editor) {
                    search_editor.finish();
                    m_reset_buffer_on_search_end = false;
                    return false;
                });

                printf("\n");
                fflush(stdout);

                auto search_prompt = "\x1b[32msearch:\x1b[0m ";
                auto search_string_result = m_search_editor->get_line(search_prompt);

                remove_child(*m_search_editor);
                m_search_editor = nullptr;
                m_is_searching = false;
                m_search_offset = 0;

                // Re-enable the notifier after discarding the search editor.
                m_notifier->set_enabled(true);

                if (search_string_result.is_error()) {
                    // Somethine broke, fail
                    m_input_error = search_string_result.error();
                    finish();
                    return;
                }

                auto& search_string = search_string_result.value();

                // Manually cleanup the search line.
                reposition_cursor();
                auto search_metrics = actual_rendered_string_metrics(search_string);
                auto metrics = actual_rendered_string_metrics(search_prompt);
                VT::clear_lines(0, metrics.lines_with_addition(search_metrics, m_num_columns));

                reposition_cursor();

                if (!m_reset_buffer_on_search_end || search_metrics.total_length == 0) {
                    // If the entry was empty, or we purposely quit without a newline,
                    // do not return anything; instead, just end the search.
                    end_search();
                    continue;
                }

                // Return the string,
                finish();
                continue;
            }
            continue;
        }
        // ^T
        if (codepoint == ctrl('T')) {
            if (m_cursor > 0 && m_buffer.size() >= 2) {
                if (m_cursor < m_buffer.size())
                    ++m_cursor;
                swap(m_buffer[m_cursor - 1], m_buffer[m_cursor - 2]);
                // FIXME: Update anchored styles too.
                m_refresh_needed = true;
            }
            continue;
        }
        if (codepoint == '\n') {
            finish();
            continue;
        }

        insert(codepoint);
    }

    if (consumed_codepoints == m_incomplete_data.size()) {
        m_incomplete_data.clear();
    } else {
        for (size_t i = 0; i < consumed_codepoints; ++i)
            m_incomplete_data.take_first();
    }
}

bool Editor::search(const StringView& phrase, bool allow_empty, bool from_beginning)
{

    int last_matching_offset = -1;

    // Do not search for empty strings.
    if (allow_empty || phrase.length() > 0) {
        size_t search_offset = m_search_offset;
        for (size_t i = m_history_cursor; i > 0; --i) {
            auto contains = from_beginning ? m_history[i - 1].starts_with(phrase) : m_history[i - 1].contains(phrase);
            if (contains) {
                last_matching_offset = i - 1;
                if (search_offset == 0)
                    break;
                --search_offset;
            }
        }

        if (last_matching_offset == -1) {
            fputc('\a', stdout);
            fflush(stdout);
        }
    }

    m_buffer.clear();
    m_cursor = 0;
    if (last_matching_offset >= 0) {
        insert(m_history[last_matching_offset]);
    }
    // Always needed, as we have cleared the buffer above.
    m_refresh_needed = true;
    return last_matching_offset >= 0;
}

void Editor::recalculate_origin()
{
    // Changing the columns can affect our origin if
    // the new size is smaller than our prompt, which would
    // cause said prompt to take up more space, so we should
    // compensate for that.
    if (m_cached_prompt_metrics.max_line_length >= m_num_columns) {
        auto added_lines = (m_cached_prompt_metrics.max_line_length + 1) / m_num_columns - 1;
        m_origin_row += added_lines;
    }

    // We also need to recalculate our cursor position,
    // but that will be calculated and applied at the next
    // refresh cycle.
}
void Editor::cleanup()
{
    auto current_buffer_metrics = actual_rendered_string_metrics(buffer_view());
    auto new_lines = current_prompt_metrics().lines_with_addition(current_buffer_metrics, m_num_columns);
    auto shown_lines = num_lines();
    if (new_lines < shown_lines)
        m_extra_forward_lines = max(shown_lines - new_lines, m_extra_forward_lines);

    VT::move_relative(-m_extra_forward_lines, m_pending_chars.size() - m_chars_inserted_in_the_middle);
    auto current_line = cursor_line();

    // There's a newline at the top, don't clear that line.
    if (current_prompt_metrics().line_lengths.first() == 0)
        --current_line;
    VT::clear_lines(current_line - 1, num_lines() - current_line + m_extra_forward_lines);
    m_extra_forward_lines = 0;
    reposition_cursor();
};

void Editor::refresh_display()
{
    auto has_cleaned_up = false;
    // Someone changed the window size, figure it out
    // and react to it, we might need to redraw.
    if (m_was_resized) {
        if (m_previous_num_columns != m_num_columns) {
            // We need to cleanup and redo everything.
            m_cached_prompt_valid = false;
            m_refresh_needed = true;
            swap(m_previous_num_columns, m_num_columns);
            recalculate_origin();
            cleanup();
            swap(m_previous_num_columns, m_num_columns);
            has_cleaned_up = true;
        }
        m_was_resized = false;
    }
    // Do not call hook on pure cursor movement.
    if (m_cached_prompt_valid && !m_refresh_needed && m_pending_chars.size() == 0) {
        // Probably just moving around.
        reposition_cursor();
        m_cached_buffer_metrics = actual_rendered_string_metrics(buffer_view());
        return;
    }
    // We might be at the last line, and have more than one line;
    // Refreshing the display will cause the terminal to scroll,
    // so note that fact and bring origin up.
    auto current_num_lines = num_lines();
    if (m_origin_row + current_num_lines > m_num_lines + 1) {
        if (current_num_lines > m_num_lines)
            m_origin_row = 0;
        else
            m_origin_row = m_num_lines - current_num_lines + 1;
    }

    if (on_display_refresh)
        on_display_refresh(*this);

    if (m_cached_prompt_valid) {
        if (!m_refresh_needed && m_cursor == m_buffer.size()) {
            // Just write the characters out and continue,
            // no need to refresh the entire line.
            char null = 0;
            m_pending_chars.append(&null, 1);
            fputs((char*)m_pending_chars.data(), stdout);
            m_pending_chars.clear();
            m_drawn_cursor = m_cursor;
            m_cached_buffer_metrics = actual_rendered_string_metrics(buffer_view());
            fflush(stdout);
            return;
        }
    }

    // Ouch, reflow entire line.
    if (!has_cleaned_up) {
        cleanup();
    }
    VT::move_absolute(m_origin_row, m_origin_column);

    fputs(m_new_prompt.characters(), stdout);

    VT::clear_to_end_of_line();
    HashMap<u32, Style> empty_styles {};
    StringBuilder builder;
    for (size_t i = 0; i < m_buffer.size(); ++i) {
        auto ends = m_spans_ending.get(i).value_or(empty_styles);
        auto starts = m_spans_starting.get(i).value_or(empty_styles);

        auto anchored_ends = m_anchored_spans_ending.get(i).value_or(empty_styles);
        auto anchored_starts = m_anchored_spans_starting.get(i).value_or(empty_styles);

        if (ends.size() || anchored_ends.size()) {
            Style style;

            for (auto& applicable_style : ends)
                style.unify_with(applicable_style.value);

            for (auto& applicable_style : anchored_ends)
                style.unify_with(applicable_style.value);

            // Disable any style that should be turned off.
            VT::apply_style(style, false);

            // Reapply styles for overlapping spans that include this one.
            style = find_applicable_style(i);
            VT::apply_style(style, true);
        }
        if (starts.size() || anchored_starts.size()) {
            Style style;

            for (auto& applicable_style : starts)
                style.unify_with(applicable_style.value);

            for (auto& applicable_style : anchored_starts)
                style.unify_with(applicable_style.value);

            // Set new styles.
            VT::apply_style(style, true);
        }
        builder.clear();
        builder.append(Utf32View { &m_buffer[i], 1 });
        fputs(builder.to_string().characters(), stdout);
    }

    VT::apply_style(Style::reset_style()); // don't bleed to EOL

    m_pending_chars.clear();
    m_refresh_needed = false;
    m_cached_buffer_metrics = actual_rendered_string_metrics(buffer_view());
    m_chars_inserted_in_the_middle = 0;
    if (!m_cached_prompt_valid) {
        m_cached_prompt_valid = true;
    }

    reposition_cursor();
    fflush(stdout);
}

void Editor::strip_styles(bool strip_anchored)
{
    m_spans_starting.clear();
    m_spans_ending.clear();

    if (strip_anchored) {
        m_anchored_spans_starting.clear();
        m_anchored_spans_ending.clear();
    }

    m_refresh_needed = true;
}

void Editor::reposition_cursor(bool to_end)
{
    auto cursor = m_cursor;
    auto saved_cursor = m_cursor;
    if (to_end)
        cursor = m_buffer.size();

    m_cursor = cursor;
    m_drawn_cursor = cursor;

    auto line = cursor_line() - 1;
    auto column = offset_in_line();

    VT::move_absolute(line + m_origin_row, column + m_origin_column);

    m_cursor = saved_cursor;
}

void VT::move_absolute(u32 row, u32 col)
{
    printf("\033[%d;%dH", row, col);
    fflush(stdout);
}

void VT::move_relative(int row, int col)
{
    char x_op = 'A', y_op = 'D';

    if (row > 0)
        x_op = 'B';
    else
        row = -row;
    if (col > 0)
        y_op = 'C';
    else
        col = -col;

    if (row > 0)
        printf("\033[%d%c", row, x_op);
    if (col > 0)
        printf("\033[%d%c", col, y_op);
}

Style Editor::find_applicable_style(size_t offset) const
{
    // Walk through our styles and merge all that fit in the offset.
    auto style = Style::reset_style();
    auto unify = [&](auto& entry) {
        if (entry.key >= offset)
            return;
        for (auto& style_value : entry.value) {
            if (style_value.key <= offset)
                return;
            style.unify_with(style_value.value, true);
        }
    };

    for (auto& entry : m_spans_starting) {
        unify(entry);
    }

    for (auto& entry : m_anchored_spans_starting) {
        unify(entry);
    }

    return style;
}

String Style::Background::to_vt_escape() const
{
    if (is_default())
        return "";

    if (m_is_rgb) {
        return String::format("\033[48;2;%d;%d;%dm", m_rgb_color[0], m_rgb_color[1], m_rgb_color[2]);
    } else {
        return String::format("\033[%dm", (u8)m_xterm_color + 40);
    }
}

String Style::Foreground::to_vt_escape() const
{
    if (is_default())
        return "";

    if (m_is_rgb) {
        return String::format("\033[38;2;%d;%d;%dm", m_rgb_color[0], m_rgb_color[1], m_rgb_color[2]);
    } else {
        return String::format("\033[%dm", (u8)m_xterm_color + 30);
    }
}

String Style::Hyperlink::to_vt_escape(bool starting) const
{
    if (is_empty())
        return "";

    return String::format("\033]8;;%s\033\\", starting ? m_link.characters() : "");
}

void Style::unify_with(const Style& other, bool prefer_other)
{
    // Unify colors.
    if (prefer_other || m_background.is_default())
        m_background = other.background();

    if (prefer_other || m_foreground.is_default())
        m_foreground = other.foreground();

    // Unify graphic renditions.
    if (other.bold())
        set(Bold);

    if (other.italic())
        set(Italic);

    if (other.underline())
        set(Underline);

    // Unify links.
    if (prefer_other || m_hyperlink.is_empty())
        m_hyperlink = other.hyperlink();
}

String Style::to_string() const
{
    StringBuilder builder;
    builder.append("Style { ");

    if (!m_foreground.is_default()) {
        builder.append("Foreground(");
        if (m_foreground.m_is_rgb) {
            builder.join(", ", m_foreground.m_rgb_color);
        } else {
            builder.appendf("(XtermColor) %d", m_foreground.m_xterm_color);
        }
        builder.append("), ");
    }

    if (!m_background.is_default()) {
        builder.append("Background(");
        if (m_background.m_is_rgb) {
            builder.join(' ', m_background.m_rgb_color);
        } else {
            builder.appendf("(XtermColor) %d", m_background.m_xterm_color);
        }
        builder.append("), ");
    }

    if (bold())
        builder.append("Bold, ");

    if (underline())
        builder.append("Underline, ");

    if (italic())
        builder.append("Italic, ");

    if (!m_hyperlink.is_empty())
        builder.appendf("Hyperlink(\"%s\"), ", m_hyperlink.m_link.characters());

    builder.append("}");

    return builder.build();
}

void VT::apply_style(const Style& style, bool is_starting)
{
    if (is_starting) {
        printf(
            "\033[%d;%d;%dm%s%s%s",
            style.bold() ? 1 : 22,
            style.underline() ? 4 : 24,
            style.italic() ? 3 : 23,
            style.background().to_vt_escape().characters(),
            style.foreground().to_vt_escape().characters(),
            style.hyperlink().to_vt_escape(true).characters());
    } else {
        printf("%s", style.hyperlink().to_vt_escape(false).characters());
    }
}

void VT::clear_lines(size_t count_above, size_t count_below)
{
    // Go down count_below lines.
    if (count_below > 0)
        printf("\033[%dB", (int)count_below);
    // Then clear lines going upwards.
    for (size_t i = count_below + count_above; i > 0; --i)
        fputs(i == 1 ? "\033[2K" : "\033[2K\033[A", stdout);
}

void VT::save_cursor()
{
    fputs("\033[s", stdout);
    fflush(stdout);
}

void VT::restore_cursor()
{
    fputs("\033[u", stdout);
    fflush(stdout);
}

void VT::clear_to_end_of_line()
{
    fputs("\033[K", stdout);
    fflush(stdout);
}

StringMetrics Editor::actual_rendered_string_metrics(const StringView& string) const
{
    size_t length { 0 };
    StringMetrics metrics;
    VTState state { Free };
    Utf8View view { string };
    auto it = view.begin();

    for (; it != view.end(); ++it) {
        auto c = *it;
        auto it_copy = it;
        ++it_copy;
        auto next_c = it_copy == view.end() ? 0 : *it_copy;
        state = actual_rendered_string_length_step(metrics, length, c, next_c, state);
    }

    metrics.line_lengths.append(length);

    for (auto& line : metrics.line_lengths)
        metrics.max_line_length = max(line, metrics.max_line_length);

    return metrics;
}

StringMetrics Editor::actual_rendered_string_metrics(const Utf32View& view) const
{
    size_t length { 0 };
    StringMetrics metrics;
    VTState state { Free };

    for (size_t i = 0; i < view.length(); ++i) {
        auto c = view.codepoints()[i];
        auto next_c = i + 1 < view.length() ? view.codepoints()[i + 1] : 0;
        state = actual_rendered_string_length_step(metrics, length, c, next_c, state);
    }

    metrics.line_lengths.append(length);

    for (auto& line : metrics.line_lengths)
        metrics.max_line_length = max(line, metrics.max_line_length);

    return metrics;
}

Editor::VTState Editor::actual_rendered_string_length_step(StringMetrics& metrics, size_t& length, u32 c, u32 next_c, VTState state) const
{
    switch (state) {
    case Free:
        if (c == '\x1b') { // escape
            return Escape;
        }
        if (c == '\r') { // carriage return
            length = 0;
            if (!metrics.line_lengths.is_empty())
                metrics.line_lengths.last() = 0;
            return state;
        }
        if (c == '\n') { // return
            metrics.line_lengths.append(length);
            length = 0;
            return state;
        }
        // FIXME: This will not support anything sophisticated
        ++length;
        ++metrics.total_length;
        return state;
    case Escape:
        if (c == ']') {
            if (next_c == '0')
                state = Title;
            return state;
        }
        if (c == '[') {
            return Bracket;
        }
        // FIXME: This does not support non-VT (aside from set-title) escapes
        return state;
    case Bracket:
        if (isdigit(c)) {
            return BracketArgsSemi;
        }
        return state;
    case BracketArgsSemi:
        if (c == ';') {
            return Bracket;
        }
        if (!isdigit(c))
            state = Free;
        return state;
    case Title:
        if (c == 7)
            state = Free;
        return state;
    }
    return state;
}

Vector<size_t, 2> Editor::vt_dsr()
{
    char buf[16];
    u32 length { 0 };

    // Read whatever junk there is before talking to the terminal
    // and insert them later when we're reading user input.
    bool more_junk_to_read { false };
    timeval timeout { 0, 0 };
    fd_set readfds;
    FD_ZERO(&readfds);
    FD_SET(0, &readfds);

    do {
        more_junk_to_read = false;
        (void)select(1, &readfds, nullptr, nullptr, &timeout);
        if (FD_ISSET(0, &readfds)) {
            auto nread = read(0, buf, 16);
            if (nread < 0) {
                m_input_error = Error::ReadFailure;
                finish();
                break;
            }

            if (nread == 0)
                break;

            m_incomplete_data.append(buf, nread);
            more_junk_to_read = true;
        }
    } while (more_junk_to_read);

    if (m_input_error.has_value())
        return { 1, 1 };

    fputs("\033[6n", stdout);
    fflush(stdout);

    do {
        auto nread = read(0, buf + length, 16 - length);
        if (nread < 0) {
            if (errno == 0) {
                // ????
                continue;
            }
            dbg() << "Error while reading DSR: " << strerror(errno);
            m_input_error = Error::ReadFailure;
            finish();
            return { 1, 1 };
        }
        if (nread == 0) {
            m_input_error = Error::Empty;
            finish();
            dbg() << "Terminal DSR issue; received no response";
            return { 1, 1 };
        }
        length += nread;
    } while (buf[length - 1] != 'R' && length < 16);
    size_t row { 1 }, col { 1 };

    if (buf[0] == '\033' && buf[1] == '[') {
        auto parts = StringView(buf + 2, length - 3).split_view(';');
        auto row_opt = parts[0].to_int();
        if (!row_opt.has_value()) {
            dbg() << "Terminal DSR issue; received garbage row";
        } else {
            row = row_opt.value();
        }
        auto col_opt = parts[1].to_int();
        if (!col_opt.has_value()) {
            dbg() << "Terminal DSR issue; received garbage col";
        } else {
            col = col_opt.value();
        }
    }
    return { row, col };
}

String Editor::line(size_t up_to_index) const
{
    StringBuilder builder;
    builder.append(Utf32View { m_buffer.data(), min(m_buffer.size(), up_to_index) });
    return builder.build();
}

bool Editor::should_break_token(Vector<u32, 1024>& buffer, size_t index)
{
    switch (m_configuration.split_mechanism) {
    case Configuration::TokenSplitMechanism::Spaces:
        return buffer[index] == ' ';
    case Configuration::TokenSplitMechanism::UnescapedSpaces:
        return buffer[index] == ' ' && (index == 0 || buffer[index - 1] != '\\');
    }

    ASSERT_NOT_REACHED();
    return true;
};

void Editor::remove_at_index(size_t index)
{
    // See if we have any anchored styles, and reposition them if needed.
    readjust_anchored_styles(index, ModificationKind::Removal);
    auto cp = m_buffer[index];
    m_buffer.remove(index);
    if (cp == '\n')
        ++m_extra_forward_lines;
}

void Editor::readjust_anchored_styles(size_t hint_index, ModificationKind modification)
{
    struct Anchor {
        Span old_span;
        Span new_span;
        Style style;
    };
    Vector<Anchor> anchors_to_relocate;
    auto index_shift = modification == ModificationKind::Insertion ? 1 : -1;
    auto forced_removal = modification == ModificationKind::ForcedOverlapRemoval;

    for (auto& start_entry : m_anchored_spans_starting) {
        for (auto& end_entry : start_entry.value) {
            if (forced_removal) {
                if (start_entry.key <= hint_index && end_entry.key > hint_index) {
                    // Remove any overlapping regions.
                    continue;
                }
            }
            if (start_entry.key >= hint_index) {
                if (start_entry.key == hint_index && end_entry.key == hint_index + 1 && modification == ModificationKind::Removal) {
                    // Remove the anchor, as all its text was wiped.
                    continue;
                }
                // Shift everything.
                anchors_to_relocate.append({ { start_entry.key, end_entry.key, Span::Mode::CodepointOriented }, { start_entry.key + index_shift, end_entry.key + index_shift, Span::Mode::CodepointOriented }, end_entry.value });
                continue;
            }
            if (end_entry.key > hint_index) {
                // Shift just the end.
                anchors_to_relocate.append({ { start_entry.key, end_entry.key, Span::Mode::CodepointOriented }, { start_entry.key, end_entry.key + index_shift, Span::Mode::CodepointOriented }, end_entry.value });
                continue;
            }
            anchors_to_relocate.append({ { start_entry.key, end_entry.key, Span::Mode::CodepointOriented }, { start_entry.key, end_entry.key, Span::Mode::CodepointOriented }, end_entry.value });
        }
    }

    m_anchored_spans_ending.clear();
    m_anchored_spans_starting.clear();
    // Pass over the relocations and update the stale entries.
    for (auto& relocation : anchors_to_relocate) {
        stylize(relocation.new_span, relocation.style);
    }
}

size_t StringMetrics::lines_with_addition(const StringMetrics& offset, size_t column_width) const
{
    size_t lines = 0;

    for (size_t i = 0; i < line_lengths.size() - 1; ++i)
        lines += (line_lengths[i] + column_width) / column_width;

    auto last = line_lengths.last();
    last += offset.line_lengths.first();
    lines += (last + column_width) / column_width;

    for (size_t i = 1; i < offset.line_lengths.size(); ++i)
        lines += (offset.line_lengths[i] + column_width) / column_width;

    return lines;
}
}