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+// SPDX-License-Identifier: GPL-2.0-or-later
+/** @file Syntax coloring via Gtksourceview and Pango markup.
+ */
+/* Authors:
+ *   Rafael Siejakowski <rs@rs-math.net>
+ *
+ * Copyright (C) 2022 Authors
+ *
+ * Released under GNU GPL v2+, read the file 'COPYING' for more information.
+ */
+
+#ifndef SEEN_UI_UI_SYNTAX_H
+#define SEEN_UI_UI_SYNTAX_H
+
+#include <memory>
+#include <optional>
+#include <vector>
+#include <gtkmm/textview.h>
+#include <glibmm.h>
+#include <glibmm/ustring.h>
+
+#include "color.h"
+
+namespace Inkscape::UI::Syntax {
+
+/** The style of a single element in a (Pango markup)-enabled widget. */
+struct Style
+{
+    std::optional<Glib::ustring> color;
+    std::optional<Glib::ustring> background;
+    uint8_t bold      : 1;
+    uint8_t italic    : 1;
+    uint8_t underline : 1;
+
+    Style()
+        : bold{false}
+        , italic{false}
+        , underline{false}
+    {}
+
+    bool isDefault() const { return !color && !background && !bold && !italic && !underline; }
+    Glib::ustring openingTag() const;
+    Glib::ustring closingTag() const;
+};
+
+/** The styles used for simple XML syntax highlighting. */
+struct XMLStyles
+{
+    Style prolog;
+    Style comment;
+    Style angular_brackets;
+    Style tag_name;
+    Style attribute_name;
+    Style attribute_value;
+    Style content;
+    Style error;
+};
+
+/** @brief A formatter for XML syntax, based on Pango markup.
+ *
+ * This mechanism is used in the TreeView in the XML Dialog,
+ * where the syntax highlighting of XML tags is accomplished
+ * via Pango markup.
+ */
+class XMLFormatter
+{
+public:
+    XMLFormatter() = default;
+    XMLFormatter(XMLStyles &&styles)
+        : _style{styles}
+    {}
+
+    void setStyle(XMLStyles const &new_style) { _style = new_style; }
+    void setStyle(XMLStyles &&new_style) { _style = new_style; }
+
+    void openTag(char const *tag_name);
+    void addAttribute(char const *attribute_name, char const *attribute_value);
+    Glib::ustring finishTag(bool self_close = false);
+
+    Glib::ustring formatContent(char const* content, bool wrap_in_quotes = true) const;
+    Glib::ustring formatComment(char const* comment, bool wrap_in_comment_marks = true) const;
+    Glib::ustring formatProlog(char const* prolog) const { return _format(_style.prolog, prolog); }
+
+private:
+    Glib::ustring _format(Style const &style, Glib::ustring const &content) const;
+    Glib::ustring _format(Style const &style, char const *content) const
+    {
+        return style.openingTag() + Glib::Markup::escape_text(content) + style.closingTag();
+    }
+
+    XMLStyles _style;
+    Glib::ustring _wip;
+};
+
+/// Build XML styles from a GTKSourceView syntax color theme.
+XMLStyles build_xml_styles(const Glib::ustring& syntax_theme);
+
+/// Syntax highlighting mode (language).
+enum class SyntaxMode
+{
+    PlainText,     ///< Plain text (no highlighting).
+    InlineCss,     ///< Inline CSS (contents of a style="..." attribute).
+    CssStyle,      ///< File-scope CSS (contents of a CSS file or a <style> tag).
+    SvgPathData,   ///< Contents of the 'd' attribute of the SVG <path> element.
+    SvgPolyPoints  ///< Contents of the 'points' attribute of <polyline> or <polygon>.
+};
+
+/// Base class for styled text editing widget.
+class TextEditView
+{
+public:
+    virtual ~TextEditView() = default;
+    virtual void setStyle(const Glib::ustring& theme) = 0;
+    virtual void setText(const Glib::ustring& text) = 0;
+    virtual Glib::ustring getText() const = 0;
+    virtual Gtk::TextView& getTextView() const = 0;
+
+    static std::unique_ptr<TextEditView> create(SyntaxMode mode);
+};
+
+} // namespace Inkscape::UI::Syntax
+
+#endif // SEEN_UI_UI_SYNTAX_H
+
+/*
+  Local Variables:
+  mode:c++
+  c-file-style:"stroustrup"
+  c-file-offsets:((innamespace . 0)(inline-open . 0)(case-label . +))
+  indent-tabs-mode:nil
+  fill-column:99
+  End:
+*/
+// vim: filetype=cpp:expandtab:shiftwidth=4:tabstop=8:softtabstop=4:fileencoding=utf-8:textwidth=99 :