Highlight changed parts in "Correct Texts"

Closes #34

TODO.md

@@ -2,6 +2,7 @@ Gaupol 1.5
 ==========
 
 * [ ] Add support for building a Flatpak
+* [x] Highlight changed parts in "Correct Texts" (#34)
 * [x] Add keybinding Ctrl+I for toggling italic (#118)
 * [x] Add keybinding Ctrl+I for toggling italic while editing (#118)
 * [x] Change keybinding for Invert Selection to Ctrl+J

gaupol/assistants.py

@@ -833,17 +833,19 @@ def __init__(self, assistant):
         self._init_tree_view()
         self._init_values()
 
-    def _add_text_column(self, index, title):
+    def _add_text_column(self, index, ref_index, title):
         """Add a multiline text column to the tree view."""
-        renderer = gaupol.MultilineCellRenderer()
+        renderer = gaupol.MultilineDiffCellRenderer()
         renderer.set_show_lengths(True)
         renderer.props.editable = (index == 4)
         renderer.props.ellipsize = Pango.EllipsizeMode.END
         renderer.props.font = gaupol.util.get_font()
+        renderer.props.ref_type = ref_index - index
         renderer.props.yalign = 0
         renderer.props.xpad = 4
         renderer.props.ypad = 4
-        column = Gtk.TreeViewColumn(title, renderer, text=index)
+        column = Gtk.TreeViewColumn(
+            title, renderer, text=index, ref_text=ref_index)
         column.set_resizable(True)
         column.set_expand(True)
         self._tree_view.append_column(column)
@@ -892,8 +894,8 @@ def _init_tree_view(self):
         if gaupol.conf.editor.use_zebra_stripes:
             callback = self._on_renderer_set_background
             column.set_cell_data_func(renderer, callback, None)
-        self._add_text_column(3, _("Original Text"))
-        self._add_text_column(4, _("Corrected Text"))
+        self._add_text_column(3, 4, _("Original Text"))
+        self._add_text_column(4, 3, _("Corrected Text"))
         column = self._tree_view.get_column(2)
         renderer = column.get_cells()[0]
         renderer.connect("edited", self._on_tree_view_cell_edited)

gaupol/config.py

@@ -61,6 +61,9 @@
     },
     "general": {
         "dark_theme": False,
+        "diff_color_change": "#ffff0033",
+        "diff_color_delete": "#ff555533",
+        "diff_color_insert": "#00ff0033",
         "version": None,
     },
     "editor": {

gaupol/renderers/__init__.py

@@ -20,11 +20,13 @@
 from .float     import FloatCellRenderer
 from .integer   import IntegerCellRenderer
 from .multiline import MultilineCellRenderer
+from .multiline import MultilineDiffCellRenderer
 from .time      import TimeCellRenderer
 
 __all__ = (
     "FloatCellRenderer",
     "IntegerCellRenderer",
     "MultilineCellRenderer",
+    "MultilineDiffCellRenderer",
     "TimeCellRenderer",
 )

gaupol/renderers/multiline.py

@@ -18,6 +18,7 @@
 """Cell renderer for multiline text data."""
 
 import aeidon
+import difflib
 import gaupol
 import math
 import re
@@ -28,7 +29,7 @@
 from gi.repository import GObject
 from gi.repository import Gtk
 
-__all__ = ("MultilineCellRenderer",)
+__all__ = ("MultilineCellRenderer", "MultilineDiffCellRenderer")
 
 
 class CellTextView(Gtk.TextView, Gtk.CellEditable):
@@ -221,11 +222,80 @@ def _text_to_markup(self, text, show_lengths, length_unit):
         # We don't actually use the length_unit argument,
         # but do need it accounted for in memoized values.
         if not text: return ""
-        if not show_lengths:
-            return GLib.markup_escape_text(text)
+        text = GLib.markup_escape_text(text)
+        if not show_lengths: return text
+        lines = text.split("\n")
         lengths = gaupol.ruler.get_lengths(text)
+        return "\n".join(("{} <small>[{:d}]</small>"
+                          .format(lines[i], lengths[i])
+                          if lines[i] else lines[i]
+                          for i in range(len(lines))))
+
+
+class MultilineDiffCellRenderer(MultilineCellRenderer):
+
+    """Cell renderer for multiline diffed text data."""
+
+    __gtype_name__ = "MultilineDiffCellRenderer"
+
+    ref_text = GObject.Property(type=str, default="")
+    ref_type = GObject.Property(type=int, default=-1)
+
+    COLOR_CHANGE = gaupol.conf.general.diff_color_change
+    COLOR_DELETE = gaupol.conf.general.diff_color_delete
+    COLOR_INSERT = gaupol.conf.general.diff_color_insert
+
+    def __init__(self):
+        """Initialize a :class:`MultilineDiffCellRenderer` instance."""
+        MultilineCellRenderer.__init__(self)
+        self._ref_text = ""
+
+    def _add_diff_markup(self, a, b):
+        """Return `a` with markup for parts different from `b`."""
+        matcher = difflib.SequenceMatcher(a=a, b=b)
+        ops = matcher.get_opcodes()
+        return "".join(self._highlight(a[i1:i2], tag)
+                       for tag, i1, i2, j1, j2 in ops)
+
+    def _get_diff_color(self, tag):
+        """Return color to use to highlight changes of type `tag`."""
+        if tag == "insert" and self.props.ref_type > 0: return self.COLOR_INSERT
+        if tag == "insert" and self.props.ref_type < 0: return self.COLOR_DELETE
+        if tag == "delete" and self.props.ref_type > 0: return self.COLOR_DELETE
+        if tag == "delete" and self.props.ref_type < 0: return self.COLOR_INSERT
+        return self.COLOR_CHANGE
+
+    def _highlight(self, text, tag):
+        """Return `text` as markup highlighting changes of type `tag`."""
+        if tag == "equal": return text
+        color = self._get_diff_color(tag)
+        return '<span background="{}">{}</span>'.format(color, text)
+
+    def _on_notify_text(self, *args):
+        """Set markup by adding line lengths to text."""
+        # Since GTK+ 3.6, the notify::text signal seems to get
+        # emitted insanely often even if text hasn't changed at
+        # all. Let's try to keep this callback as fast as possible.
+        self._text = self.props.text
+        self._ref_text = self.props.ref_text
+        self.props.markup = self._text_to_markup(self.props.text,
+                                                 self.props.ref_text,
+                                                 self._show_lengths,
+                                                 gaupol.conf.editor.length_unit)
+
+    @aeidon.deco.memoize(1000)
+    def _text_to_markup(self, text, ref_text, show_lengths, length_unit):
+        """Return `text` rendered as markup for display."""
+        # We don't actually use the length_unit argument,
+        # but do need it accounted for in memoized values.
+        if not text: return ""
         text = GLib.markup_escape_text(text)
+        ref_text = GLib.markup_escape_text(ref_text)
+        with aeidon.util.silent(Exception, tb=True):
+            text = self._add_diff_markup(text, ref_text)
+        if not show_lengths: return text
         lines = text.split("\n")
+        lengths = gaupol.ruler.get_lengths(text)
         return "\n".join(("{} <small>[{:d}]</small>"
                           .format(lines[i], lengths[i])
                           if lines[i] else lines[i]

gaupol/renderers/test/test_multiline.py

@@ -41,3 +41,26 @@ def run_renderer(self):
 
     def setup_method(self, method):
         self.renderer = gaupol.MultilineCellRenderer()
+
+
+class TestMultilineDiffCellRenderer(gaupol.TestCase):
+
+    def run_renderer(self):
+        tree_view = Gtk.TreeView()
+        tree_view.set_headers_visible(False)
+        store = Gtk.ListStore(str, str)
+        store.append(("test", "test\ntest"))
+        tree_view.set_model(store)
+        self.renderer.props.editable = True
+        column = Gtk.TreeViewColumn("", self.renderer, text=1, ref_text=0)
+        tree_view.append_column(column)
+        window = Gtk.Window()
+        window.connect("delete-event", Gtk.main_quit)
+        window.set_position(Gtk.WindowPosition.CENTER)
+        window.set_default_size(240, 70)
+        window.add(tree_view)
+        window.show_all()
+        Gtk.main()
+
+    def setup_method(self, method):
+        self.renderer = gaupol.MultilineDiffCellRenderer()