[gitg] Fix unstage_patch by reversing applying patch

[Jesse van den Kieboom <jessevdk src gnome org>]

commit 92d891bd4ed4d52af497cd4b53ac221976abf375
Author: Jesse van den Kieboom <jessevdk gmail com>
Date:   Sun Jan 5 20:10:46 2014 +0100

    Fix unstage_patch by reversing applying patch

 libgitg/gitg-stage.vala |   37 ++++++++++++++++++++++++++++++++++++-
 1 files changed, 36 insertions(+), 1 deletions(-)
---
diff --git a/libgitg/gitg-stage.vala b/libgitg/gitg-stage.vala
index 9cca512..de55461 100644
--- a/libgitg/gitg-stage.vala
+++ b/libgitg/gitg-stage.vala
@@ -55,6 +55,39 @@ public class PatchSet
 
        public string  filename;
        public Patch[] patches;
+
+       public PatchSet reversed()
+       {
+               var ret = new PatchSet();
+
+               ret.filename = filename;
+               ret.patches = new Patch[patches.length];
+
+               for (int i = 0; i < patches.length; i++)
+               {
+                       var orig = patches[i];
+
+                       var p = Patch() {
+                               old_offset = orig.new_offset,
+                               new_offset = orig.old_offset,
+                               length = orig.length
+                       };
+
+                       switch (patches[i].type)
+                       {
+                               case Type.ADD:
+                                       p.type = Type.REMOVE;
+                                       break;
+                               case Type.REMOVE:
+                                       p.type = Type.ADD;
+                                       break;
+                       }
+
+                       ret.patches[i] = p;
+               }
+
+               return ret;
+       }
 }
 
 public class Stage : Object
@@ -755,7 +788,9 @@ public class Stage : Object
                        var head_stream = new MemoryInputStream.from_bytes(new Bytes(head_content));
                        var index_stream = new MemoryInputStream.from_bytes(new Bytes(index_content));
 
-                       apply_patch(index, head_stream, index_stream, patch);
+                       var reversed = patch.reversed();
+
+                       apply_patch(index, index_stream, head_stream, reversed);
 
                        head_stream.close();
                        index_stream.close();