1 files changed, 89 insertions, 0 deletions
diff --git a/src/changes.hh b/src/changes.hh
new file mode 100644
index 00000000..963ca786
--- /dev/null
+++ b/src/changes.hh
@@ -0,0 +1,89 @@
+#ifndef changes_hh_INCLUDED
+#define changes_hh_INCLUDED
+
+#include "buffer.hh"
+#include "coord.hh"
+
+namespace Kakoune
+{
+
+// This tracks position changes for changes that are done
+// in a forward way (each change takes place at a position)
+// *after* the previous one.
+struct ForwardChangesTracker
+{
+    BufferCoord cur_pos; // last change position at current modification
+    BufferCoord old_pos; // last change position at start
+
+    void update(const Buffer::Change& change);
+    void update(const Buffer& buffer, size_t& timestamp);
+
+    BufferCoord get_old_coord(BufferCoord coord) const;
+    BufferCoord get_new_coord(BufferCoord coord) const;
+    BufferCoord get_new_coord_tolerant(BufferCoord coord) const;
+
+    bool relevant(const Buffer::Change& change, BufferCoord old_coord) const;
+};
+
+const Buffer::Change* forward_sorted_until(const Buffer::Change* first, const Buffer::Change* last);
+const Buffer::Change* backward_sorted_until(const Buffer::Change* first, const Buffer::Change* last);
+
+template<typename RangeContainer>
+void update_forward(ConstArrayView<Buffer::Change> changes, RangeContainer& ranges)
+{
+    ForwardChangesTracker changes_tracker;
+
+    auto change_it = changes.begin();
+    auto advance_while_relevant = [&](const BufferCoord& pos) mutable {
+        while (change_it != changes.end() and changes_tracker.relevant(*change_it, pos))
+            changes_tracker.update(*change_it++);
+    };
+
+    for (auto& range : ranges)
+    {
+        auto& first = get_first(range);
+        auto& last = get_last(range);
+        advance_while_relevant(first);
+        first = changes_tracker.get_new_coord_tolerant(first);
+
+        advance_while_relevant(last);
+        last = changes_tracker.get_new_coord_tolerant(last);
+    }
+}
+
+template<typename RangeContainer>
+void update_backward(ConstArrayView<Buffer::Change> changes, RangeContainer& ranges)
+{
+    ForwardChangesTracker changes_tracker;
+
+    using ReverseIt = std::reverse_iterator<const Buffer::Change*>;
+    auto change_it = ReverseIt(changes.end());
+    auto change_end = ReverseIt(changes.begin());
+    auto advance_while_relevant = [&](const BufferCoord& pos) mutable {
+        while (change_it != change_end)
+        {
+            auto change = *change_it;
+            change.begin = changes_tracker.get_new_coord(change.begin);
+            change.end = changes_tracker.get_new_coord(change.end);
+            if (not changes_tracker.relevant(change, pos))
+                break;
+            changes_tracker.update(change);
+            ++change_it;
+        }
+    };
+
+    for (auto& range : ranges)
+    {
+        auto& first = get_first(range);
+        auto& last = get_last(range);
+        advance_while_relevant(first);
+        first = changes_tracker.get_new_coord_tolerant(first);
+
+        advance_while_relevant(last);
+        last = changes_tracker.get_new_coord_tolerant(last);
+    }
+}
+
+}
+
+#endif // changes_hh_INCLUDED