Add function that maintains the dependency graph.

The function takes care that all edges are present in the dependency
graph.

This fixes a bug that when adding a todo with a parent which appears
later in the file, the edge wouldn't be drawn.

TodoList.py

@@ -53,6 +53,29 @@ class TodoList(object):
 
         return hits[0] if len(hits) else None
 
+    def _maintain_dep_graph(self, p_todo):
+        """
+        Makes sure that the dependency graph is consistent according to the
+        given todo.
+        """
+
+        dep_id = p_todo.tag_value('id')
+        # maintain dependency graph
+        if dep_id:
+            self._depgraph.add_node(p_todo.number)
+
+            # connect all tasks we have in memory so far that refer to this
+            # task
+            for dep in \
+                [dep for dep in self._todos if dep.has_tag('p', dep_id)]:
+
+                self._depgraph.add_edge(p_todo.number, dep.number, dep_id)
+
+        for child in p_todo.tag_values('p'):
+            parent = self.todo_by_dep_id(child)
+            if parent:
+                self._depgraph.add_edge(parent.number, p_todo.number, child)
+
     def add(self, p_src):
         """
         Given a todo string, parse it and put it to the end of the list.
@@ -76,14 +99,7 @@ class TodoList(object):
             todo = Todo.Todo(p_src, number)
             self._todos.append(todo)
 
-            # maintain dependency graph
-            if todo.has_tag('id'):
-                self._depgraph.add_node(todo.number)
-
-            for child in todo.tag_values('p'):
-                parent = self.todo_by_dep_id(child)
-                if parent:
-                    self._depgraph.add_edge(parent.number, todo.number, child)
+            self._maintain_dep_graph(todo)
 
     def delete(self, p_number):
         """ Deletes a todo item from the list. """

test/TodoListTest.py

@@ -133,6 +133,7 @@ class TodoListDependencyTester(unittest.TestCase):
         self.todolist.add("Bar p:1")
         self.todolist.add("Baz p:1 id:2")
         self.todolist.add("Buzz p:2")
+        self.todolist.add("Fnord")
 
     def test_check_dep(self):
         children = self.todolist.children(1)
@@ -158,6 +159,12 @@ class TodoListDependencyTester(unittest.TestCase):
         self.assertEqual(self.todolist.children(2), [])
         self.assertEqual(self.todolist.parents(1), [])
 
+    def test_add_dep(self):
+        self.todolist.add_dependency(5, 4)
+
+        self.assertTrue(self.todolist.todo(5).has_tag('id', '3'))
+        self.assertTrue(self.todolist.todo(4).has_tag('p', '3'))
+
     def test_remove_dep1(self):
         self.todolist.remove_dependency(3, 4)
 
@@ -168,7 +175,7 @@ class TodoListDependencyTester(unittest.TestCase):
         old = str(self.todolist)
         self.todolist.remove_dependency(1, 4)
 
-        self.assertEquals(str(self.todolist),old)
+        self.assertEquals(str(self.todolist), old)
 
     def test_remove_task(self):
         self.todolist.delete(3)