diff --git a/jedi/refactoring.py b/jedi/refactoring.py
index 91837f2a..8ddb52a2 100644
--- a/jedi/refactoring.py
+++ b/jedi/refactoring.py
@@ -1,23 +1,80 @@
 """ Introduce refactoring """
 
 import api
+import modules
+import difflib
 
 
 class Refactoring(object):
-    def __init__(self, changed_lines, renamed_files):
-        self.changed_lines = changed_lines
-        self.renamed_files = renamed_files
+    def __init__(self, change_dct):
+        """
+        :param change_dct: dict(old_path=(new_path, old_lines, new_lines))
+        """
+        self.change_dct = change_dct
+
+    def old_files(self):
+        dct = {}
+        for old_path, (new_path, old_l, new_l) in self.change_dct.items():
+            dct[new_path] = '\n'.join(new_l)
+        return dct
+
+    def new_files(self):
+        dct = {}
+        for old_path, (new_path, old_l, new_l) in self.change_dct.items():
+            dct[new_path] = '\n'.join(new_l)
+        return dct
 
     def diff(self):
-        return ''
+        texts = []
+        for old_path, (new_path, old_l, new_l) in self.change_dct.items():
+            print old_path, new_path, old_l, new_l
+            if old_path:
+                udiff = difflib.unified_diff(old_l, new_l)
+            else:
+                udiff = difflib.unified_diff(old_l, new_l, old_path, new_path)
+            texts.append('\n'.join(udiff))
+        return '\n'.join(texts)
 
 
-def rename(new_name, *args, **kwargs):
+def rename(new_name, source, *args, **kwargs):
     """ The `args` / `kwargs` params are the same as in `api.Script`.
     :param operation: The refactoring operation to execute.
     :type operation: str
+    :type source: str
     :return: list of changed lines/changed files
     """
-    script = api.Script(*args, **kwargs)
+    dct = {}
+    def process(path, old_lines, new_lines):
+        if new_lines is not None:  # goto next file, save last
+            dct[path] = path, old_lines, new_lines
+
+    script = api.Script(source, *args, **kwargs)
     old_names = script.related_names()
-    return []
+    order = sorted(old_names, key=lambda x: (x.module_path, x.start_pos),
+                            reverse=True)
+
+    current_path = object()
+    new_lines = old_lines = None
+    for name in order:
+        assert isinstance(name, api.api_classes.RelatedName)
+        if name.in_builtin_module():
+            continue
+        if current_path != name.module_path:
+            current_path = name.module_path
+
+            process(current_path, old_lines, new_lines)
+            if current_path is not None:
+                # None means take the source that is a normal param.
+                with open(current_path) as f:
+                    source = f.read()
+
+            new_lines = modules.source_to_unicode(source).splitlines()
+            old_lines = new_lines[:]
+
+        nr, indent = name.start_pos
+        line = new_lines[nr - 1]
+        new_lines[nr - 1] = line[:indent] + new_name + \
+                            line[indent + len(name.name_part):]
+
+    process(current_path, old_lines, new_lines)
+    return Refactoring(dct)