dialog: add text-area widget

This patch moves the text-editing facility of app/text_area to a
text-area widget as part of the dialog library. This has two benefits.
First, it simplifies app/text_area by using the dialog API. Second, the
editor can now easily be reused by other dialog-API-based applications.

Fixes #5058

repos/gems/include/dialog/text_area_widget.h

@@ -0,0 +1,224 @@
+/*
+ * \brief  Text dialog
+ * \author Norman Feske
+ * \date   2020-01-14
+ */
+
+/*
+ * Copyright (C) 2020-2023 Genode Labs GmbH
+ *
+ * This file is part of the Genode OS framework, which is distributed
+ * under the terms of the GNU Affero General Public License version 3.
+ */
+
+#ifndef _INCLUDE__DIALOG__TEXT_AREA_WIDGET_H_
+#define _INCLUDE__DIALOG__TEXT_AREA_WIDGET_H_
+
+/* Genode includes */
+#include <util/reconstructible.h>
+#include <util/utf8.h>
+#include <dialog/widgets.h>
+#include <gems/dynamic_array.h>
+
+namespace Dialog { struct Text_area_widget; }
+
+
+struct Dialog::Text_area_widget : Widget<Vbox>
+{
+	public:
+
+		struct Action : Interface, Noncopyable
+		{
+			virtual void trigger_copy() = 0;
+			virtual void trigger_paste() = 0;
+			virtual void trigger_save() = 0;
+			virtual void refresh_text_area() = 0;
+		};
+
+	private:
+
+		Allocator &_alloc;
+
+		struct Character : Codepoint
+		{
+			Character(Codepoint &codepoint) : Codepoint(codepoint) { }
+
+			void print(Output &out) const
+			{
+				if (value == '"')
+					Genode::print(out, "&quot;");
+				else if (value == 9)
+					Genode::print(out, " ");
+				else
+					Codepoint::print(out);
+			}
+		};
+
+		using Line = Dynamic_array<Character>;
+		using Text = Dynamic_array<Line>;
+
+		Text _text { _alloc };
+
+		struct Position
+		{
+			Line::Index x;
+			Text::Index y;
+
+			bool operator != (Position const &other) const
+			{
+				return (x.value != other.x.value) || (y.value != other.y.value);
+			}
+		};
+
+		Position _cursor { { 0 }, { 0 } };
+
+		Position _scroll { { 0 }, { 0 } };
+
+		Constructible<Position> _hovered_position { };
+
+		unsigned _max_lines = ~0U;
+
+		bool _editable = false;
+
+		unsigned _modification_count = 0;
+
+		struct Selection
+		{
+			Constructible<Position> start;
+			Constructible<Position> end;
+
+			void clear()
+			{
+				start.destruct();
+				end  .destruct();
+			}
+
+			bool defined() const
+			{
+				return start.constructed() && end.constructed() && (*start != *end);
+			}
+
+			template <typename FN>
+			void for_each_selected_line(FN const &) const;
+
+			template <typename FN>
+			void with_selection_at_line(Text::Index y, Line const &, FN const &) const;
+
+			/* generate dialog model */
+			void view_selected_line(Scope<Hbox, Float, Label> &, Text::Index, Line const &) const;
+		};
+
+		bool _drag    = false;
+		bool _shift   = false;
+		bool _control = false;
+
+		Selection _selection { };
+
+		static bool _printable(Codepoint code)
+		{
+			if (!code.valid())
+				return false;
+
+			if (code.value == '\t')
+				return true;
+
+			return (code.value >= 0x20 && code.value < 0xf000);
+		}
+
+		bool _cursor_at_last_line() const
+		{
+			return (_cursor.y.value + 1 >= _text.upper_bound().value);
+		}
+
+		bool _cursor_at_end_of_line() const
+		{
+			bool result = false;
+			_text.apply(_cursor.y, [&] (Line &line) {
+				result = (_cursor.x.value >= line.upper_bound().value); });
+			return result;
+		}
+
+		void _tie_cursor_to_end_of_line()
+		{
+			_text.apply(_cursor.y, [&] (Line &line) {
+				if (_cursor.x.value > line.upper_bound().value)
+					_cursor.x = line.upper_bound(); });
+		}
+
+		bool _end_of_text() const
+		{
+			return _cursor_at_last_line() && _cursor_at_end_of_line();
+		}
+
+		void _clamp_scroll_position_to_upper_bound()
+		{
+			if (_max_lines != ~0U)
+				if (_scroll.y.value + _max_lines > _text.upper_bound().value)
+					_scroll.y.value = max(_text.upper_bound().value, _max_lines)
+					                - _max_lines;
+		}
+
+		void _sanitize_scroll_position();
+		void _move_characters(Line &, Line &);
+		void _delete_selection();
+		void _insert_printable(Codepoint);
+		void _handle_printable(Codepoint);
+		void _handle_backspace();
+		void _handle_delete();
+		void _handle_newline();
+		void _handle_left();
+		void _handle_right();
+		void _handle_up();
+		void _handle_down();
+		void _handle_pageup();
+		void _handle_pagedown();
+		void _handle_home();
+		void _handle_end();
+
+		void _with_position_at(At const &, auto const &) const;
+
+	public:
+
+		Text_area_widget(Allocator &alloc) : _alloc(alloc) { clear(); }
+
+		void view(Scope<Vbox> &) const;
+
+		void click(Clicked_at const &);
+		void clack(Clacked_at const &, Action &);
+		void drag (Dragged_at const &);
+
+		void editable(bool editable) { _editable = editable; }
+
+		unsigned modification_count() const { return _modification_count; }
+
+		void max_lines(unsigned max_lines) { _max_lines = max_lines; }
+
+		void handle_event(Event const &, Action &);
+
+		void move_cursor_to(::Dialog::At const &);
+
+		void clear();
+
+		void append_newline() { _text.append(_alloc); }
+
+		void append_character(Codepoint c);
+
+		/* insert character and advance cursor */
+		void insert_at_cursor_position(Codepoint);
+
+		void gen_clipboard_content(Xml_generator &xml) const;
+
+		template <typename FN>
+		void for_each_character(FN const &fn) const
+		{
+			_text.for_each([&] (Text::Index at, Line const &line) {
+				line.for_each([&] (Line::Index, Character c) {
+					fn(c); });
+
+				if (at.value + 1 < _text.upper_bound().value)
+					fn(Codepoint{'\n'});
+			});
+		}
+};
+
+#endif /* _INCLUDE__DIALOG__TEXT_AREA_WIDGET_H_ */