LibVT: Factor out terminal emulation from Terminal to make it reusable

Now that we're bringing back the in-kernel virtual console, we should
move towards having a single implementation of terminal emulation.

This patch rips out the emulation code from the Terminal application
and turns it into the beginnings of LibVT.

The basic design idea is that users of VT::Terminal will implement and
provide a VT::TerminalClient subclass to handle presentation-specific
things. We'll need to iterate on this, but it's a start. :^)

3 files changed, 84 insertions, 1141 deletions

diff --git a/Applications/Makefile.common b/Applications/Makefile.common
index 8935cb38be..90302abafc 100755
--- a/Applications/Makefile.common
+++ b/Applications/Makefile.common
@@ -3,7 +3,7 @@ DEFINES += -DUSERLAND
 all: $(APP)
 
 $(APP): $(OBJS)
-	$(LD) -o $(APP) $(LDFLAGS) $(OBJS) -lgui -ldraw -laudio -lipc -lcore -lc
+	$(LD) -o $(APP) $(LDFLAGS) $(OBJS) -lgui -ldraw -laudio -lipc -lvt -lcore -lc
 
 .cpp.o:
 	@echo "CXX $<"; $(CXX) $(CXXFLAGS) -o $@ -c $<
diff --git a/Applications/Terminal/Terminal.cpp b/Applications/Terminal/Terminal.cpp
index ba83a1e7c7..5fd56b25a2 100644
--- a/Applications/Terminal/Terminal.cpp
+++ b/Applications/Terminal/Terminal.cpp
@@ -4,11 +4,11 @@
 #include <AK/StdLibExtras.h>
 #include <AK/StringBuilder.h>
 #include <Kernel/KeyCode.h>
+#include <LibDraw/Font.h>
 #include <LibGUI/GApplication.h>
 #include <LibGUI/GClipboard.h>
 #include <LibGUI/GPainter.h>
 #include <LibGUI/GWindow.h>
-#include <LibDraw/Font.h>
 #include <errno.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -17,13 +17,12 @@
 #include <unistd.h>
 
 //#define TERMINAL_DEBUG
-u8 Terminal::Attribute::default_foreground_color = 7;
-u8 Terminal::Attribute::default_background_color = 0;
 
 Terminal::Terminal(int ptm_fd, RefPtr<CConfigFile> config)
-    : m_ptm_fd(ptm_fd)
+    : m_terminal(*this)
+    , m_ptm_fd(ptm_fd)
     , m_notifier(ptm_fd, CNotifier::Read)
-    , m_config(config)
+    , m_config(move(config))
 {
     set_frame_shape(FrameShape::Container);
     set_frame_shadow(FrameShadow::Sunken);
@@ -59,916 +58,24 @@ Terminal::Terminal(int ptm_fd, RefPtr<CConfigFile> config)
             return;
         }
         for (ssize_t i = 0; i < nread; ++i)
-            on_char(buffer[i]);
+            m_terminal.on_char(buffer[i]);
         flush_dirty_lines();
     };
 
     m_line_height = font().glyph_height() + m_line_spacing;
 
-    set_size(m_config->read_num_entry("Window", "Width", 80),
-        m_config->read_num_entry("Window", "Height", 25));
-}
-
-Terminal::Line::Line(u16 length)
-{
-    set_length(length);
-}
-
-Terminal::Line::~Line()
-{
-    delete[] characters;
-    delete[] attributes;
-}
-
-void Terminal::Line::set_length(u16 new_length)
-{
-    if (m_length == new_length)
-        return;
-    auto* new_characters = new u8[new_length];
-    auto* new_attributes = new Attribute[new_length];
-    memset(new_characters, ' ', new_length);
-    if (characters && attributes) {
-        memcpy(new_characters, characters, min(m_length, new_length));
-        memcpy(new_attributes, attributes, min(m_length, new_length) * sizeof(Attribute));
-    }
-    delete[] characters;
-    delete[] attributes;
-    characters = new_characters;
-    attributes = new_attributes;
-    m_length = new_length;
-}
-
-void Terminal::Line::clear(Attribute attribute)
-{
-    if (dirty) {
-        memset(characters, ' ', m_length);
-        for (u16 i = 0; i < m_length; ++i)
-            attributes[i] = attribute;
-        return;
-    }
-    for (unsigned i = 0; i < m_length; ++i) {
-        if (characters[i] != ' ')
-            dirty = true;
-        characters[i] = ' ';
-    }
-    for (unsigned i = 0; i < m_length; ++i) {
-        if (attributes[i] != attribute)
-            dirty = true;
-        attributes[i] = attribute;
-    }
+    m_terminal.set_size(m_config->read_num_entry("Window", "Width", 80), m_config->read_num_entry("Window", "Height", 25));
 }
 
 Terminal::~Terminal()
 {
 }
 
-void Terminal::clear()
-{
-    for (size_t i = 0; i < rows(); ++i)
-        line(i).clear(m_current_attribute);
-    set_cursor(0, 0);
-}
-
-inline bool is_valid_parameter_character(u8 ch)
-{
-    return ch >= 0x30 && ch <= 0x3f;
-}
-
-inline bool is_valid_intermediate_character(u8 ch)
-{
-    return ch >= 0x20 && ch <= 0x2f;
-}
-
-inline bool is_valid_final_character(u8 ch)
-{
-    return ch >= 0x40 && ch <= 0x7e;
-}
-
 static inline Color lookup_color(unsigned color)
 {
     return Color::from_rgb(xterm_colors[color]);
 }
 
-void Terminal::escape$h_l(bool should_set, bool question_param, const ParamVector& params)
-{
-    int mode = 2;
-    if (params.size() > 0) {
-        mode = params[0];
-    }
-    if (!question_param) {
-        switch (mode) {
-            // FIXME: implement *something* for this
-        default:
-            unimplemented_escape();
-            break;
-        }
-    } else {
-        switch (mode) {
-        case 25:
-            // Hide cursor command, but doesn't need to be run (for now, because
-            // we don't do inverse control codes anyways)
-            if (should_set)
-                dbgprintf("Terminal: Hide Cursor escapecode recieved. Not needed: ignored.\n");
-            else
-                dbgprintf("Terminal: Show Cursor escapecode recieved. Not needed: ignored.\n");
-            break;
-        default:
-            break;
-        }
-    }
-}
-
-void Terminal::escape$m(const ParamVector& params)
-{
-    if (params.is_empty()) {
-        m_current_attribute.reset();
-        return;
-    }
-    if (params.size() == 3 && params[1] == 5) {
-        if (params[0] == 38) {
-            m_current_attribute.foreground_color = params[2];
-            return;
-        } else if (params[0] == 48) {
-            m_current_attribute.background_color = params[2];
-            return;
-        }
-    }
-    for (auto param : params) {
-        switch (param) {
-        case 0:
-            // Reset
-            m_current_attribute.reset();
-            break;
-        case 1:
-            m_current_attribute.flags |= Attribute::Bold;
-            break;
-        case 3:
-            m_current_attribute.flags |= Attribute::Italic;
-            break;
-        case 4:
-            m_current_attribute.flags |= Attribute::Underline;
-            break;
-        case 5:
-            m_current_attribute.flags |= Attribute::Blink;
-            break;
-        case 7:
-            m_current_attribute.flags |= Attribute::Negative;
-            break;
-        case 22:
-            m_current_attribute.flags &= ~Attribute::Bold;
-            break;
-        case 23:
-            m_current_attribute.flags &= ~Attribute::Italic;
-            break;
-        case 24:
-            m_current_attribute.flags &= ~Attribute::Underline;
-            break;
-        case 25:
-            m_current_attribute.flags &= ~Attribute::Blink;
-            break;
-        case 27:
-            m_current_attribute.flags &= ~Attribute::Negative;
-            break;
-        case 30:
-        case 31:
-        case 32:
-        case 33:
-        case 34:
-        case 35:
-        case 36:
-        case 37:
-            // Foreground color
-            if (m_current_attribute.flags & Attribute::Bold)
-                param += 8;
-            m_current_attribute.foreground_color = param - 30;
-            break;
-        case 39:
-            // reset foreground
-            m_current_attribute.foreground_color = Attribute::default_foreground_color;
-            break;
-        case 40:
-        case 41:
-        case 42:
-        case 43:
-        case 44:
-        case 45:
-        case 46:
-        case 47:
-            // Background color
-            if (m_current_attribute.flags & Attribute::Bold)
-                param += 8;
-            m_current_attribute.background_color = param - 40;
-            break;
-        case 49:
-            // reset background
-            m_current_attribute.background_color = Attribute::default_background_color;
-            break;
-        default:
-            dbgprintf("FIXME: escape$m: p: %u\n", param);
-        }
-    }
-}
-
-void Terminal::escape$s(const ParamVector&)
-{
-    m_saved_cursor_row = m_cursor_row;
-    m_saved_cursor_column = m_cursor_column;
-}
-
-void Terminal::escape$u(const ParamVector&)
-{
-    set_cursor(m_saved_cursor_row, m_saved_cursor_column);
-}
-
-void Terminal::escape$t(const ParamVector& params)
-{
-    if (params.size() < 1)
-        return;
-    dbgprintf("FIXME: escape$t: Ps: %u (param count: %d)\n", params[0], params.size());
-}
-
-void Terminal::escape$r(const ParamVector& params)
-{
-    unsigned top = 1;
-    unsigned bottom = m_rows;
-    if (params.size() >= 1)
-        top = params[0];
-    if (params.size() >= 2)
-        bottom = params[1];
-    if ((bottom - top) < 2 || bottom > m_rows) {
-        dbgprintf("Error: escape$r: scrolling region invalid: %u-%u\n", top, bottom);
-        return;
-    }
-    m_scroll_region_top = top - 1;
-    m_scroll_region_bottom = bottom - 1;
-    set_cursor(0, 0);
-}
-
-void Terminal::escape$H(const ParamVector& params)
-{
-    unsigned row = 1;
-    unsigned col = 1;
-    if (params.size() >= 1)
-        row = params[0];
-    if (params.size() >= 2)
-        col = params[1];
-    set_cursor(row - 1, col - 1);
-}
-
-void Terminal::escape$A(const ParamVector& params)
-{
-    int num = 1;
-    if (params.size() >= 1)
-        num = params[0];
-    if (num == 0)
-        num = 1;
-    int new_row = (int)m_cursor_row - num;
-    if (new_row < 0)
-        new_row = 0;
-    set_cursor(new_row, m_cursor_column);
-}
-
-void Terminal::escape$B(const ParamVector& params)
-{
-    int num = 1;
-    if (params.size() >= 1)
-        num = params[0];
-    if (num == 0)
-        num = 1;
-    int new_row = (int)m_cursor_row + num;
-    if (new_row >= m_rows)
-        new_row = m_rows - 1;
-    set_cursor(new_row, m_cursor_column);
-}
-
-void Terminal::escape$C(const ParamVector& params)
-{
-    int num = 1;
-    if (params.size() >= 1)
-        num = params[0];
-    if (num == 0)
-        num = 1;
-    int new_column = (int)m_cursor_column + num;
-    if (new_column >= m_columns)
-        new_column = m_columns - 1;
-    set_cursor(m_cursor_row, new_column);
-}
-
-void Terminal::escape$D(const ParamVector& params)
-{
-    int num = 1;
-    if (params.size() >= 1)
-        num = params[0];
-    if (num == 0)
-        num = 1;
-    int new_column = (int)m_cursor_column - num;
-    if (new_column < 0)
-        new_column = 0;
-    set_cursor(m_cursor_row, new_column);
-}
-
-void Terminal::escape$G(const ParamVector& params)
-{
-    int new_column = 1;
-    if (params.size() >= 1)
-        new_column = params[0] - 1;
-    if (new_column < 0)
-        new_column = 0;
-    set_cursor(m_cursor_row, new_column);
-}
-
-void Terminal::escape$b(const ParamVector& params)
-{
-    if (params.size() < 1)
-        return;
-
-    for (unsigned i = 0; i < params[0]; ++i)
-        put_character_at(m_cursor_row, m_cursor_column++, m_last_char);
-}
-
-void Terminal::escape$d(const ParamVector& params)
-{
-    int new_row = 1;
-    if (params.size() >= 1)
-        new_row = params[0] - 1;
-    if (new_row < 0)
-        new_row = 0;
-    set_cursor(new_row, m_cursor_column);
-}
-
-void Terminal::escape$X(const ParamVector& params)
-{
-    // Erase characters (without moving cursor)
-    int num = 1;
-    if (params.size() >= 1)
-        num = params[0];
-    if (num == 0)
-        num = 1;
-    // Clear from cursor to end of line.
-    for (int i = m_cursor_column; i < num; ++i) {
-        put_character_at(m_cursor_row, i, ' ');
-    }
-}
-
-void Terminal::escape$K(const ParamVector& params)
-{
-    int mode = 0;
-    if (params.size() >= 1)
-        mode = params[0];
-    switch (mode) {
-    case 0:
-        // Clear from cursor to end of line.
-        for (int i = m_cursor_column; i < m_columns; ++i) {
-            put_character_at(m_cursor_row, i, ' ');
-        }
-        break;
-    case 1:
-        // Clear from cursor to beginning of line.
-        for (int i = 0; i < m_cursor_column; ++i) {
-            put_character_at(m_cursor_row, i, ' ');
-        }
-        break;
-    case 2:
-        // Clear the complete line
-        for (int i = 0; i < m_columns; ++i) {
-            put_character_at(m_cursor_row, i, ' ');
-        }
-        break;
-    default:
-        unimplemented_escape();
-        break;
-    }
-}
-
-void Terminal::escape$J(const ParamVector& params)
-{
-    int mode = 0;
-    if (params.size() >= 1)
-        mode = params[0];
-    switch (mode) {
-    case 0:
-        // Clear from cursor to end of screen.
-        for (int i = m_cursor_column; i < m_columns; ++i)
-            put_character_at(m_cursor_row, i, ' ');
-        for (int row = m_cursor_row + 1; row < m_rows; ++row) {
-            for (int column = 0; column < m_columns; ++column) {
-                put_character_at(row, column, ' ');
-            }
-        }
-        break;
-    case 1:
-        /// Clear from cursor to beginning of screen
-        for (int i = m_cursor_column - 1; i >= 0; --i)
-            put_character_at(m_cursor_row, i, ' ');
-        for (int row = m_cursor_row - 1; row >= 0; --row) {
-            for (int column = 0; column < m_columns; ++column) {
-                put_character_at(row, column, ' ');
-            }
-        }
-        break;
-    case 2:
-        clear();
-        break;
-    case 3:
-        // FIXME: <esc>[3J should also clear the scrollback buffer.
-        clear();
-        break;
-    default:
-        unimplemented_escape();
-        break;
-    }
-}
-
-void Terminal::escape$S(const ParamVector& params)
-{
-    int count = 1;
-    if (params.size() >= 1)
-        count = params[0];
-
-    for (u16 i = 0; i < count; i++)
-        scroll_up();
-}
-
-void Terminal::escape$T(const ParamVector& params)
-{
-    int count = 1;
-    if (params.size() >= 1)
-        count = params[0];
-
-    for (u16 i = 0; i < count; i++)
-        scroll_down();
-}
-
-void Terminal::escape$L(const ParamVector& params)
-{
-    int count = 1;
-    if (params.size() >= 1)
-        count = params[0];
-    invalidate_cursor();
-    for (; count > 0; --count) {
-        m_lines.insert(m_cursor_row + m_scroll_region_top, make<Line>(m_columns));
-        if (m_scroll_region_bottom + 1 < m_lines.size())
-            m_lines.remove(m_scroll_region_bottom + 1);
-        else
-            m_lines.remove(m_lines.size() - 1);
-    }
-    m_need_full_flush = true;
-}
-
-void Terminal::escape$M(const ParamVector& params)
-{
-    int count = 1;
-    if (params.size() >= 1)
-        count = params[0];
-
-    if (count == 1 && m_cursor_row == 0) {
-        scroll_up();
-        return;
-    }
-
-    int max_count = m_rows - (m_scroll_region_top + m_cursor_row);
-    count = min(count, max_count);
-
-    for (int c = count; c > 0; --c) {
-        m_lines.remove(m_cursor_row + m_scroll_region_top);
-        if (m_scroll_region_bottom < m_lines.size())
-            m_lines.insert(m_scroll_region_bottom, make<Line>(m_columns));
-        else
-            m_lines.append(make<Line>(m_columns));
-    }
-}
-
-void Terminal::escape$P(const ParamVector& params)
-{
-    int num = 1;
-    if (params.size() >= 1)
-        num = params[0];
-
-    if (num == 0)
-        num = 1;
-
-    auto& line = this->line(m_cursor_row);
-
-    // Move n characters of line to the left
-    for (int i = m_cursor_column; i < line.m_length - num; i++)
-        line.characters[i] = line.characters[i + num];
-
-    // Fill remainder of line with blanks
-    for (int i = line.m_length - num; i < line.m_length; i++)
-        line.characters[i] = ' ';
-
-    line.dirty = true;
-}
-
-void Terminal::execute_xterm_command()
-{
-    m_final = '@';
-    bool ok;
-    unsigned value = String::copy(m_xterm_param1).to_uint(ok);
-    if (ok) {
-        switch (value) {
-        case 0:
-        case 1:
-        case 2:
-            set_window_title(String::copy(m_xterm_param2));
-            break;
-        default:
-            unimplemented_xterm_escape();
-            break;
-        }
-    }
-    m_xterm_param1.clear_with_capacity();
-    m_xterm_param2.clear_with_capacity();
-}
-
-void Terminal::execute_escape_sequence(u8 final)
-{
-    bool question_param = false;
-    m_final = final;
-    ParamVector params;
-
-    if (m_parameters.size() > 0 && m_parameters[0] == '?') {
-        question_param = true;
-        m_parameters.remove(0);
-    }
-    auto paramparts = String::copy(m_parameters).split(';');
-    for (auto& parampart : paramparts) {
-        bool ok;
-        unsigned value = parampart.to_uint(ok);
-        if (!ok) {
-            // FIXME: Should we do something else?
-            m_parameters.clear_with_capacity();
-            m_intermediates.clear_with_capacity();
-            return;
-        }
-        params.append(value);
-    }
-
-#if defined(TERMINAL_DEBUG)
-    dbgprintf("Terminal::execute_escape_sequence: Handled final '%c'\n", final);
-    dbgprintf("Params: ");
-    for (auto& p : params) {
-        dbgprintf("%d ", p);
-    }
-    dbgprintf("\b\n");
-#endif
-
-    switch (final) {
-    case 'A':
-        escape$A(params);
-        break;
-    case 'B':
-        escape$B(params);
-        break;
-    case 'C':
-        escape$C(params);
-        break;
-    case 'D':
-        escape$D(params);
-        break;
-    case 'H':
-        escape$H(params);
-        break;
-    case 'J':
-        escape$J(params);
-        break;
-    case 'K':
-        escape$K(params);
-        break;
-    case 'M':
-        escape$M(params);
-        break;
-    case 'P':
-        escape$P(params);
-        break;
-    case 'S':
-        escape$S(params);
-        break;
-    case 'T':
-        escape$T(params);
-        break;
-    case 'L':
-        escape$L(params);
-        break;
-    case 'G':
-        escape$G(params);
-        break;
-    case 'X':
-        escape$X(params);
-        break;
-    case 'b':
-        escape$b(params);
-        break;
-    case 'd':
-        escape$d(params);
-        break;
-    case 'm':
-        escape$m(params);
-        break;
-    case 's':
-        escape$s(params);
-        break;
-    case 'u':
-        escape$u(params);
-        break;
-    case 't':
-        escape$t(params);
-        break;
-    case 'r':
-        escape$r(params);
-        break;
-    case 'l':
-        escape$h_l(true, question_param, params);
-        break;
-    case 'h':
-        escape$h_l(false, question_param, params);
-        break;
-    default:
-        dbgprintf("Terminal::execute_escape_sequence: Unhandled final '%c'\n", final);
-        break;
-    }
-
-#if defined(TERMINAL_DEBUG)
-    dbgprintf("\n");
-    for (auto& line : m_lines) {
-        dbgprintf("Terminal: Line: ");
-        for (int i = 0; i < line->length; i++) {
-            dbgprintf("%c", line->characters[i]);
-        }
-        dbgprintf("\n");
-    }
-#endif
-
-    m_parameters.clear_with_capacity();
-    m_intermediates.clear_with_capacity();
-}
-
-void Terminal::newline()
-{
-    u16 new_row = m_cursor_row;
-    if (m_cursor_row == m_scroll_region_bottom) {
-        scroll_up();
-    } else {
-        ++new_row;
-    }
-    set_cursor(new_row, 0);
-}
-
-void Terminal::scroll_up()
-{
-    // NOTE: We have to invalidate the cursor first.
-    invalidate_cursor();
-    m_lines.remove(m_scroll_region_top);
-    m_lines.insert(m_scroll_region_bottom, make<Line>(m_columns));
-    m_need_full_flush = true;
-}
-
-void Terminal::scroll_down()
-{
-    // NOTE: We have to invalidate the cursor first.
-    invalidate_cursor();
-    m_lines.remove(m_scroll_region_bottom);
-    m_lines.insert(m_scroll_region_top, make<Line>(m_columns));
-    m_need_full_flush = true;
-}
-
-void Terminal::set_cursor(unsigned a_row, unsigned a_column)
-{
-    unsigned row = min(a_row, m_rows - 1u);
-    unsigned column = min(a_column, m_columns - 1u);
-    if (row == m_cursor_row && column == m_cursor_column)
-        return;
-    ASSERT(row < rows());
-    ASSERT(column < columns());
-    invalidate_cursor();
-    m_cursor_row = row;
-    m_cursor_column = column;
-    if (column != columns() - 1u)
-        m_stomp = false;
-    invalidate_cursor();
-}
-
-void Terminal::put_character_at(unsigned row, unsigned column, u8 ch)
-{
-    ASSERT(row < rows());
-    ASSERT(column < columns());
-    auto& line = this->line(row);
-    line.characters[column] = ch;
-    line.attributes[column] = m_current_attribute;
-    line.attributes[column].flags |= Attribute::Touched;
-    line.dirty = true;
-
-    m_last_char = ch;
-}
-
-void Terminal::on_char(u8 ch)
-{
-#ifdef TERMINAL_DEBUG
-    dbgprintf("Terminal::on_char: %b (%c), fg=%u, bg=%u\n", ch, ch, m_current_attribute.foreground_color, m_current_attribute.background_color);
-#endif
-    switch (m_escape_state) {
-    case ExpectBracket:
-        if (ch == '[')
-            m_escape_state = ExpectParameter;
-        else if (ch == '(') {
-            m_swallow_current = true;
-            m_escape_state = ExpectParameter;
-        } else if (ch == ']')
-            m_escape_state = ExpectXtermParameter1;
-        else
-            m_escape_state = Normal;
-        return;
-    case ExpectXtermParameter1:
-        if (ch != ';') {
-            m_xterm_param1.append(ch);
-            return;
-        }
-        m_escape_state = ExpectXtermParameter2;
-        return;
-    case ExpectXtermParameter2:
-        if (ch != '\007') {
-            m_xterm_param2.append(ch);
-            return;
-        }
-        m_escape_state = ExpectXtermFinal;
-        [[fallthrough]];
-    case ExpectXtermFinal:
-        m_escape_state = Normal;
-        if (ch == '\007')
-            execute_xterm_command();
-        return;
-    case ExpectParameter:
-        if (is_valid_parameter_character(ch)) {
-            m_parameters.append(ch);
-            return;
-        }
-        m_escape_state = ExpectIntermediate;
-        [[fallthrough]];
-    case ExpectIntermediate:
-        if (is_valid_intermediate_character(ch)) {
-            m_intermediates.append(ch);
-            return;
-        }
-        m_escape_state = ExpectFinal;
-        [[fallthrough]];
-    case ExpectFinal:
-        if (is_valid_final_character(ch)) {
-            m_escape_state = Normal;
-            if (!m_swallow_current)
-                execute_escape_sequence(ch);
-            m_swallow_current = false;
-            return;
-        }
-        m_escape_state = Normal;
-        m_swallow_current = false;
-        return;
-    case Normal:
-        break;
-    }
-
-    switch (ch) {
-    case '\0':
-        return;
-    case '\033':
-        m_escape_state = ExpectBracket;
-        m_swallow_current = false;
-        return;
-    case 8: // Backspace
-        if (m_cursor_column) {
-            set_cursor(m_cursor_row, m_cursor_column - 1);
-            put_character_at(m_cursor_row, m_cursor_column, ' ');
-            return;
-        }
-        return;
-    case '\a':
-        if (m_should_beep)
-            sysbeep();
-        else {
-            m_visual_beep_timer.restart(200);
-            m_visual_beep_timer.set_single_shot(true);
-            m_visual_beep_timer.on_timeout = [this] {
-                force_repaint();
-            };
-            force_repaint();
-        }
-        return;
-    case '\t': {
-        for (unsigned i = m_cursor_column; i < columns(); ++i) {
-            if (m_horizontal_tabs[i]) {
-                set_cursor(m_cursor_row, i);
-                return;
-            }
-        }
-        return;
-    }
-    case '\r':
-        set_cursor(m_cursor_row, 0);
-        return;
-    case '\n':
-        newline();
-        return;
-    }
-
-    auto new_column = m_cursor_column + 1;
-    if (new_column < columns()) {
-        put_character_at(m_cursor_row, m_cursor_column, ch);
-        set_cursor(m_cursor_row, new_column);
-    } else {
-        if (m_stomp) {
-            m_stomp = false;
-            newline();
-            put_character_at(m_cursor_row, m_cursor_column, ch);
-            set_cursor(m_cursor_row, 1);
-        } else {
-            // Curious: We wait once on the right-hand side
-            m_stomp = true;
-            put_character_at(m_cursor_row, m_cursor_column, ch);
-        }
-    }
-}
-
-void Terminal::inject_string(const String& str)
-{
-    for (int i = 0; i < str.length(); ++i)
-        on_char(str[i]);
-}
-
-void Terminal::unimplemented_escape()
-{
-    StringBuilder builder;
-    builder.appendf("((Unimplemented escape: %c", m_final);
-    if (!m_parameters.is_empty()) {
-        builder.append(" parameters:");
-        for (int i = 0; i < m_parameters.size(); ++i)
-            builder.append((char)m_parameters[i]);
-    }
-    if (!m_intermediates.is_empty()) {
-        builder.append(" intermediates:");
-        for (int i = 0; i < m_intermediates.size(); ++i)
-            builder.append((char)m_intermediates[i]);
-    }
-    builder.append("))");
-    inject_string(builder.to_string());
-}
-
-void Terminal::unimplemented_xterm_escape()
-{
-    auto message = String::format("((Unimplemented xterm escape: %c))\n", m_final);
-    inject_string(message);
-}
-
-void Terminal::set_size(u16 columns, u16 rows)
-{
-    if (columns == m_columns && rows == m_rows)
-        return;
-
-#if defined(TERMINAL_DEBUG)
-    dbgprintf("Terminal: RESIZE to: %d rows\n", rows);
-#endif
-
-    if (rows > m_rows) {
-        while (m_lines.size() < rows)
-            m_lines.append(make<Line>(columns));
-    } else {
-        m_lines.shrink(rows);
-    }
-
-    for (int i = 0; i < rows; ++i)
-        m_lines[i].set_length(columns);
-
-    m_columns = columns;
-    m_rows = rows;
-
-    m_scroll_region_top = 0;
-    m_scroll_region_bottom = rows - 1;
-
-    m_cursor_row = min((int)m_cursor_row, m_rows - 1);
-    m_cursor_column = min((int)m_cursor_column, m_columns - 1);
-    m_saved_cursor_row = min((int)m_saved_cursor_row, m_rows - 1);
-    m_saved_cursor_column = min((int)m_saved_cursor_column, m_columns - 1);
-
-    m_horizontal_tabs.resize(columns);
-    for (unsigned i = 0; i < columns; ++i)
-        m_horizontal_tabs[i] = (i % 8) == 0;
-    // Rightmost column is always last tab on line.
-    m_horizontal_tabs[columns - 1] = 1;
-
-    m_pixel_width = (frame_thickness() * 2) + (m_inset * 2) + (m_columns * font().glyph_width('x'));
-    m_pixel_height = (frame_thickness() * 2) + (m_inset * 2) + (m_rows * (font().glyph_height() + m_line_spacing)) - m_line_spacing;
-
-    set_size_policy(SizePolicy::Fixed, SizePolicy::Fixed);
-    set_preferred_size(m_pixel_width, m_pixel_height);
-
-    m_needs_background_fill = true;
-    force_repaint();
-
-    winsize ws;
-    ws.ws_row = rows;
-    ws.ws_col = columns;
-    int rc = ioctl(m_ptm_fd, TIOCSWINSZ, &ws);
-    ASSERT(rc == 0);
-}
-
 Rect Terminal::glyph_rect(u16 row, u16 column)
 {
     int y = row * m_line_height;
@@ -979,24 +86,11 @@ Rect Terminal::glyph_rect(u16 row, u16 column)
 Rect Terminal::row_rect(u16 row)
 {
     int y = row * m_line_height;
-    Rect rect = { frame_thickness() + m_inset, y + frame_thickness() + m_inset, font().glyph_width('x') * m_columns, font().glyph_height() };
+    Rect rect = { frame_thickness() + m_inset, y + frame_thickness() + m_inset, font().glyph_width('x') * m_terminal.columns(), font().glyph_height() };
     rect.inflate(0, m_line_spacing);
     return rect;
 }
 
-bool Terminal::Line::has_only_one_background_color() const
-{
-    if (!m_length)
-        return true;
-    // FIXME: Cache this result?
-    auto color = attributes[0].background_color;
-    for (size_t i = 1; i < m_length; ++i) {
-        if (attributes[i].background_color != color)
-            return false;
-    }
-    return true;
-}
-
 void Terminal::event(CEvent& event)
 {
     if (event.type() == GEvent::WindowBecameActive || event.type() == GEvent::WindowBecameInactive) {
@@ -1087,16 +181,16 @@ void Terminal::paint_event(GPaintEvent& event)
         painter.fill_rect(frame_inner_rect(), Color(Color::Black).with_alpha(m_opacity));
     invalidate_cursor();
 
-    for (u16 row = 0; row < m_rows; ++row) {
-        auto& line = this->line(row);
+    for (u16 row = 0; row < m_terminal.rows(); ++row) {
+        auto& line = m_terminal.line(row);
         bool has_only_one_background_color = line.has_only_one_background_color();
         if (m_visual_beep_timer.is_active())
             painter.fill_rect(row_rect(row), Color::Red);
         else if (has_only_one_background_color)
             painter.fill_rect(row_rect(row), lookup_color(line.attributes[0].background_color).with_alpha(m_opacity));
-        for (u16 column = 0; column < m_columns; ++column) {
+        for (u16 column = 0; column < m_terminal.columns(); ++column) {
             char ch = line.characters[column];
-            bool should_reverse_fill_for_cursor_or_selection = (m_cursor_blink_state && m_in_active_window && row == m_cursor_row && column == m_cursor_column)
+            bool should_reverse_fill_for_cursor_or_selection = (m_cursor_blink_state && m_in_active_window && row == m_terminal.cursor_row() && column == m_terminal.cursor_column())
                 || selection_contains({ row, column });
             auto& attribute = line.attributes[column];
             auto character_rect = glyph_rect(row, column);
@@ -1109,18 +203,18 @@ void Terminal::paint_event(GPaintEvent& event)
             painter.draw_glyph(
                 character_rect.location(),
                 ch,
-                attribute.flags & Attribute::Bold ? Font::default_bold_fixed_width_font() : font(),
+                attribute.flags & VT::Attribute::Bold ? Font::default_bold_fixed_width_font() : font(),
                 lookup_color(should_reverse_fill_for_cursor_or_selection ? attribute.background_color : attribute.foreground_color));
         }
     }
 
     if (!m_in_active_window) {
-        auto cell_rect = glyph_rect(m_cursor_row, m_cursor_column).inflated(0, m_line_spacing);
-        painter.draw_rect(cell_rect, lookup_color(line(m_cursor_row).attributes[m_cursor_column].foreground_color));
+        auto cell_rect = glyph_rect(m_terminal.cursor_row(), m_terminal.cursor_column()).inflated(0, m_line_spacing);
+        painter.draw_rect(cell_rect, lookup_color(m_terminal.line(m_terminal.cursor_row()).attributes[m_terminal.cursor_column()].foreground_color));
     }
 }
 
-void Terminal::set_window_title(const String& title)
+void Terminal::set_window_title(const StringView& title)
 {
     auto* w = window();
     if (!w)
@@ -1130,19 +224,19 @@ void Terminal::set_window_title(const String& title)
 
 void Terminal::invalidate_cursor()
 {
-    line(m_cursor_row).dirty = true;
+    m_terminal.invalidate_cursor();
 }
 
 void Terminal::flush_dirty_lines()
 {
-    if (m_need_full_flush) {
+    if (m_terminal.m_need_full_flush) {
         update();
-        m_need_full_flush = false;
+        m_terminal.m_need_full_flush = false;
         return;
     }
     Rect rect;
-    for (int i = 0; i < m_rows; ++i) {
-        if (line(i).dirty)
+    for (int i = 0; i < m_terminal.rows(); ++i) {
+        if (m_terminal.line(i).dirty)
             rect = rect.united(row_rect(i));
     }
     update(rect);
@@ -1151,8 +245,8 @@ void Terminal::flush_dirty_lines()
 void Terminal::force_repaint()
 {
     m_needs_background_fill = true;
-    for (int i = 0; i < m_rows; ++i)
-        line(i).dirty = true;
+    for (int i = 0; i < m_terminal.rows(); ++i)
+        m_terminal.line(i).dirty = true;
     update();
 }
 
@@ -1160,7 +254,7 @@ void Terminal::resize_event(GResizeEvent& event)
 {
     int new_columns = (event.size().width() - frame_thickness() * 2 - m_inset * 2) / font().glyph_width('x');
     int new_rows = (event.size().height() - frame_thickness() * 2 - m_inset * 2) / m_line_height;
-    set_size(new_columns, new_rows);
+    m_terminal.set_size(new_columns, new_rows);
 }
 
 void Terminal::apply_size_increments_to_window(GWindow& window)
@@ -1185,14 +279,14 @@ void Terminal::set_opacity(u8 new_opacity)
     force_repaint();
 }
 
-BufferPosition Terminal::normalized_selection_start() const
+VT::BufferPosition Terminal::normalized_selection_start() const
 {
     if (m_selection_start < m_selection_end)
         return m_selection_start;
     return m_selection_end;
 }
 
-BufferPosition Terminal::normalized_selection_end() const
+VT::BufferPosition Terminal::normalized_selection_end() const
 {
     if (m_selection_start < m_selection_end)
         return m_selection_end;
@@ -1201,10 +295,10 @@ BufferPosition Terminal::normalized_selection_end() const
 
 bool Terminal::has_selection() const
 {
-     return m_selection_start.is_valid() && m_selection_end.is_valid();
+    return m_selection_start.is_valid() && m_selection_end.is_valid();
 }
 
-bool Terminal::selection_contains(const BufferPosition& position) const
+bool Terminal::selection_contains(const VT::BufferPosition& position) const
 {
     if (!has_selection())
         return false;
@@ -1212,7 +306,7 @@ bool Terminal::selection_contains(const BufferPosition& position) const
     return position >= normalized_selection_start() && position <= normalized_selection_end();
 }
 
-BufferPosition Terminal::buffer_position_at(const Point& position) const
+VT::BufferPosition Terminal::buffer_position_at(const Point& position) const
 {
     auto adjusted_position = position.translated(-(frame_thickness() + m_inset), -(frame_thickness() + m_inset));
     int row = adjusted_position.y() / m_line_height;
@@ -1221,10 +315,10 @@ BufferPosition Terminal::buffer_position_at(const Point& position) const
         row = 0;
     if (column < 0)
         column = 0;
-    if (row >= m_rows)
-        row = m_rows - 1;
-    if (column >= m_columns)
-        column = m_columns - 1;
+    if (row >= m_terminal.rows())
+        row = m_terminal.rows() - 1;
+    if (column >= m_terminal.columns())
+        column = m_terminal.columns() - 1;
     return { row, column };
 }
 
@@ -1274,9 +368,9 @@ String Terminal::selected_text() const
 
     for (int row = start.row(); row <= end.row(); ++row) {
         int first_column = row == start.row() ? start.column() : 0;
-        int last_column = row == end.row() ? end.column() : m_columns - 1;
+        int last_column = row == end.row() ? end.column() : m_terminal.columns() - 1;
         for (int column = first_column; column <= last_column; ++column) {
-            auto& line = this->line(row);
+            auto& line = m_terminal.line(row);
             if (line.attributes[column].is_untouched()) {
                 builder.append('\n');
                 break;
@@ -1290,3 +384,35 @@ String Terminal::selected_text() const
 
     return builder.to_string();
 }
+
+void Terminal::terminal_did_resize(u16 columns, u16 rows)
+{
+    m_pixel_width = (frame_thickness() * 2) + (m_inset * 2) + (columns * font().glyph_width('x'));
+    m_pixel_height = (frame_thickness() * 2) + (m_inset * 2) + (rows * (font().glyph_height() + m_line_spacing)) - m_line_spacing;
+
+    set_size_policy(SizePolicy::Fixed, SizePolicy::Fixed);
+    set_preferred_size(m_pixel_width, m_pixel_height);
+
+    m_needs_background_fill = true;
+    force_repaint();
+
+    winsize ws;
+    ws.ws_row = rows;
+    ws.ws_col = columns;
+    int rc = ioctl(m_ptm_fd, TIOCSWINSZ, &ws);
+    ASSERT(rc == 0);
+}
+
+void Terminal::beep()
+{
+    if (m_should_beep) {
+        sysbeep();
+        return;
+    }
+    m_visual_beep_timer.restart(200);
+    m_visual_beep_timer.set_single_shot(true);
+    m_visual_beep_timer.on_timeout = [this] {
+        force_repaint();
+    };
+    force_repaint();
+}
diff --git a/Applications/Terminal/Terminal.h b/Applications/Terminal/Terminal.h
index 48a9defe43..3d985c56e4 100644
--- a/Applications/Terminal/Terminal.h
+++ b/Applications/Terminal/Terminal.h
@@ -1,68 +1,22 @@
 #pragma once
 
 #include <AK/AKString.h>
-#include <AK/NonnullOwnPtrVector.h>
-#include <AK/Types.h>
 #include <LibCore/CConfigFile.h>
 #include <LibCore/CNotifier.h>
 #include <LibCore/CTimer.h>
 #include <LibDraw/GraphicsBitmap.h>
 #include <LibDraw/Rect.h>
 #include <LibGUI/GFrame.h>
+#include <LibVT/Terminal.h>
 
-class Font;
-
-class BufferPosition {
-public:
-    BufferPosition() {}
-    BufferPosition(int row, int column)
-        : m_row(row)
-        , m_column(column)
-    {
-    }
-
-    bool is_valid() const { return m_row >= 0 && m_column >= 0; }
-    int row() const { return m_row; }
-    int column() const { return m_column; }
-
-    bool operator<(const BufferPosition& other) const
-    {
-        return m_row < other.m_row || (m_row == other.m_row && m_column < other.m_column);
-    }
-
-    bool operator<=(const BufferPosition& other) const
-    {
-        return *this < other || *this == other;
-    }
-
-    bool operator>=(const BufferPosition& other) const
-    {
-        return !(*this < other);
-    }
-
-    bool operator==(const BufferPosition& other) const
-    {
-        return m_row == other.m_row && m_column == other.m_column;
-    }
-
-    bool operator!=(const BufferPosition& other) const
-    {
-        return !(*this == other);
-    }
-
-private:
-    int m_row { -1 };
-    int m_column { -1 };
-};
-
-class Terminal final : public GFrame {
+class Terminal final : public GFrame
+    , public VT::TerminalClient {
     C_OBJECT(Terminal)
 public:
     explicit Terminal(int ptm_fd, RefPtr<CConfigFile> config);
     virtual ~Terminal() override;
 
     void create_window();
-    void on_char(u8);
 
     void flush_dirty_lines();
     void force_repaint();
@@ -77,15 +31,14 @@ public:
     RefPtr<CConfigFile> config() const { return m_config; }
 
     bool has_selection() const;
-    bool selection_contains(const BufferPosition&) const;
+    bool selection_contains(const VT::BufferPosition&) const;
     String selected_text() const;
-    BufferPosition buffer_position_at(const Point&) const;
-    BufferPosition normalized_selection_start() const;
-    BufferPosition normalized_selection_end() const;
+    VT::BufferPosition buffer_position_at(const Point&) const;
+    VT::BufferPosition normalized_selection_start() const;
+    VT::BufferPosition normalized_selection_end() const;
 
 private:
-    typedef Vector<unsigned, 4> ParamVector;
-
+    // ^GWidget
     virtual void event(CEvent&) override;
     virtual void paint_event(GPaintEvent&) override;
     virtual void resize_event(GResizeEvent&) override;
@@ -94,155 +47,24 @@ private:
     virtual void mousemove_event(GMouseEvent&) override;
     virtual void mouseup_event(GMouseEvent&) override;
 
-    void scroll_up();
-    void scroll_down();
-    void newline();
-    void set_cursor(unsigned row, unsigned column);
-    void put_character_at(unsigned row, unsigned column, u8 ch);
-    void invalidate_cursor();
-    void set_window_title(const String&);
+    // ^TerminalClient
+    virtual void beep() override;
+    virtual void set_window_title(const StringView&) override;
+    virtual void terminal_did_resize(u16 columns, u16 rows) override;
 
-    void inject_string(const String&);
-    void unimplemented_escape();
-    void unimplemented_xterm_escape();
 
-    void escape$A(const ParamVector&);
-    void escape$B(const ParamVector&);
-    void escape$C(const ParamVector&);
-    void escape$D(const ParamVector&);
-    void escape$H(const ParamVector&);
-    void escape$J(const ParamVector&);
-    void escape$K(const ParamVector&);
-    void escape$M(const ParamVector&);
-    void escape$P(const ParamVector&);
-    void escape$G(const ParamVector&);
-    void escape$X(const ParamVector&);
-    void escape$b(const ParamVector&);
-    void escape$d(const ParamVector&);
-    void escape$m(const ParamVector&);
-    void escape$s(const ParamVector&);
-    void escape$u(const ParamVector&);
-    void escape$t(const ParamVector&);
-    void escape$r(const ParamVector&);
-    void escape$S(const ParamVector&);
-    void escape$T(const ParamVector&);
-    void escape$L(const ParamVector&);
-    void escape$h_l(bool, bool, const ParamVector&);
-
-    void clear();
-
-    void set_size(u16 columns, u16 rows);
-    u16 columns() const { return m_columns; }
-    u16 rows() const { return m_rows; }
     Rect glyph_rect(u16 row, u16 column);
     Rect row_rect(u16 row);
-    void update_cursor();
-
-    struct Attribute {
-        Attribute() { reset(); }
 
-        static u8 default_foreground_color;
-        static u8 default_background_color;
-
-        void reset()
-        {
-            foreground_color = default_foreground_color;
-            background_color = default_background_color;
-            flags = Flags::NoAttributes;
-        }
-        u8 foreground_color;
-        u8 background_color;
-
-        enum Flags {
-            NoAttributes = 0x00,
-            Bold = 0x01,
-            Italic = 0x02,
-            Underline = 0x04,
-            Negative = 0x08,
-            Blink = 0x10,
-            Touched = 0x20,
-        };
-
-        bool is_untouched() const { return !(flags & Touched); }
-
-        // TODO: it would be really nice if we had a helper for enums that
-        // exposed bit ops for class enums...
-        int flags = Flags::NoAttributes;
-
-        bool operator==(const Attribute& other) const
-        {
-            return foreground_color == other.foreground_color && background_color == other.background_color && flags == other.flags;
-        }
-        bool operator!=(const Attribute& other) const
-        {
-            return !(*this == other);
-        }
-    };
-
-    struct Line {
-        explicit Line(u16 columns);
-        ~Line();
-        void clear(Attribute);
-        bool has_only_one_background_color() const;
-        void set_length(u16);
-        u8* characters { nullptr };
-        Attribute* attributes { nullptr };
-        bool dirty { false };
-        u16 m_length { 0 };
-    };
-    Line& line(size_t index)
-    {
-        ASSERT(index < m_rows);
-        return m_lines[index];
-    }
-    const Line& line(size_t index) const
-    {
-        ASSERT(index < m_rows);
-        return m_lines[index];
-    }
-
-    NonnullOwnPtrVector<Line> m_lines;
-
-    BufferPosition m_selection_start;
-    BufferPosition m_selection_end;
-
-    int m_scroll_region_top { 0 };
-    int m_scroll_region_bottom { 0 };
+    void update_cursor();
+    void invalidate_cursor();
 
-    u16 m_columns { 0 };
-    u16 m_rows { 0 };
+    VT::Terminal m_terminal;
 
-    u16 m_cursor_row { 0 };
-    u16 m_cursor_column { 0 };
-    u16 m_saved_cursor_row { 0 };
-    u16 m_saved_cursor_column { 0 };
-    bool m_stomp { false };
+    VT::BufferPosition m_selection_start;
+    VT::BufferPosition m_selection_end;
 
     bool m_should_beep { false };
-
-    Attribute m_current_attribute;
-
-    void execute_escape_sequence(u8 final);
-    void execute_xterm_command();
-
-    enum EscapeState {
-        Normal,
-        ExpectBracket,
-        ExpectParameter,
-        ExpectIntermediate,
-        ExpectFinal,
-
-        ExpectXtermParameter1,
-        ExpectXtermParameter2,
-        ExpectXtermFinal,
-    };
-    EscapeState m_escape_state { Normal };
-    Vector<u8> m_parameters;
-    Vector<u8> m_intermediates;
-    Vector<u8> m_xterm_param1;
-    Vector<u8> m_xterm_param2;
-    Vector<bool> m_horizontal_tabs;
-    u8 m_final { 0 };
     bool m_belling { false };
 
     int m_pixel_width { 0 };
@@ -254,10 +76,7 @@ private:
 
     int m_ptm_fd { -1 };
 
-    bool m_swallow_current { false };
-
     bool m_in_active_window { false };
-    bool m_need_full_flush { false };
 
     CNotifier m_notifier;
 
@@ -270,6 +89,4 @@ private:
     CTimer m_cursor_blink_timer;
     CTimer m_visual_beep_timer;
     RefPtr<CConfigFile> m_config;
-
-    u8 m_last_char { 0 };
 };