From fc07f6c4fad4fab905eabb3a0106a78b2bd4c82e Mon Sep 17 00:00:00 2001
From: Karl Kroening <karlk@kralnet.us>
Date: Wed, 5 Jul 2017 04:07:30 -0600
Subject: [PATCH] #17: remove `Node._parents`

---
 ffmpeg/_run.py  |  7 +++---
 ffmpeg/dag.py   | 59 +++++++++++++++++++++++++++++++------------------
 ffmpeg/nodes.py |  5 -----
 3 files changed, 41 insertions(+), 30 deletions(-)

diff --git a/ffmpeg/_run.py b/ffmpeg/_run.py
index 533160e..09a3ae5 100644
--- a/ffmpeg/_run.py
+++ b/ffmpeg/_run.py
@@ -55,7 +55,7 @@ def _get_input_args(input_node):
 def _get_filter_spec(i, node, stream_name_map):
     stream_name = _get_stream_name('v{}'.format(i))
     stream_name_map[node] = stream_name
-    inputs = [stream_name_map[parent] for parent in node._parents]
+    inputs = [stream_name_map[edge.upstream_node] for edge in node.incoming_edges]
     filter_spec = '{}{}{}'.format(''.join(inputs), node._get_filter(), stream_name)
     return filter_spec
 
@@ -75,7 +75,8 @@ def _get_global_args(node):
 def _get_output_args(node, stream_name_map):
     args = []
     if node.name != merge_outputs.__name__:
-        stream_name = stream_name_map[node._parents[0]]
+        assert len(node.incoming_edges) == 1
+        stream_name = stream_name_map[node.incoming_edges[0].upstream_node]
         if stream_name != '[0]':
             args += ['-map', stream_name]
         if node.name == output.__name__:
@@ -96,7 +97,7 @@ def get_args(node):
     """Get command-line arguments for ffmpeg."""
     args = []
     # TODO: group nodes together, e.g. `-i somefile -r somerate`.
-    sorted_nodes, child_map = topo_sort([node])
+    sorted_nodes, outgoing_edge_maps = topo_sort([node])
     del(node)
     input_nodes = [node for node in sorted_nodes if isinstance(node, InputNode)]
     output_nodes = [node for node in sorted_nodes if isinstance(node, OutputNode) and not
diff --git a/ffmpeg/dag.py b/ffmpeg/dag.py
index 181ec8e..25e8d21 100644
--- a/ffmpeg/dag.py
+++ b/ffmpeg/dag.py
@@ -96,6 +96,20 @@ class DagNode(object):
 DagEdge = namedtuple('DagEdge', ['downstream_node', 'downstream_label', 'upstream_node', 'upstream_label'])
 
 
+def get_incoming_edges(downstream_node, incoming_edge_map):
+    edges = []
+    for downstream_label, (upstream_node, upstream_label) in incoming_edge_map.items():
+        edges += [DagEdge(downstream_node, downstream_label, upstream_node, upstream_label)]
+    return edges
+
+
+def get_outgoing_edges(upstream_node, outgoing_edge_map):
+    edges = []
+    for upstream_label, (downstream_node, downstream_label) in outgoing_edge_map:
+        edges += [DagEdge(downstream_node, downstream_label, upstream_node, upstream_label)]
+    return edges
+
+
 class KwargReprNode(DagNode):
     """A DagNode that can be represented as a set of args+kwargs.
     """
@@ -142,11 +156,7 @@ class KwargReprNode(DagNode):
 
     @property
     def incoming_edges(self):
-        edges = []
-        for downstream_label, (upstream_node, upstream_label) in self.incoming_edge_map.items():
-            downstream_node = self
-            edges += [DagEdge(downstream_node, downstream_label, upstream_node, upstream_label)]
-        return edges
+        return get_incoming_edges(self, self.incoming_edge_map)
 
     @property
     def incoming_edge_map(self):
@@ -157,24 +167,29 @@ class KwargReprNode(DagNode):
         return self.name
 
 
-def topo_sort(start_nodes):
+def topo_sort(downstream_nodes):
     marked_nodes = []
     sorted_nodes = []
-    child_map = {}
-    def visit(node, child):
-        if node in marked_nodes:
+    outgoing_edge_maps = {}
+
+    def visit(upstream_node, upstream_label, downstream_node, downstream_label):
+        if upstream_node in marked_nodes:
             raise RuntimeError('Graph is not a DAG')
-        if child is not None:
-            if node not in child_map:
-                child_map[node] = []
-            child_map[node].append(child)
-        if node not in sorted_nodes:
-            marked_nodes.append(node)
-            parents = [edge.upstream_node for edge in node.incoming_edges]
-            [visit(parent, node) for parent in parents]
-            marked_nodes.remove(node)
-            sorted_nodes.append(node)
-    unmarked_nodes = list(copy.copy(start_nodes))
+
+        if downstream_node is not None:
+            if upstream_node not in outgoing_edge_maps:
+                outgoing_edge_maps[upstream_node] = {}
+            outgoing_edge_maps[upstream_node][upstream_label] = (downstream_node, downstream_label)
+
+        if upstream_node not in sorted_nodes:
+            marked_nodes.append(upstream_node)
+            for edge in upstream_node.incoming_edges:
+                visit(edge.upstream_node, edge.upstream_label, edge.downstream_node, edge.downstream_label)
+            marked_nodes.remove(upstream_node)
+            sorted_nodes.append(upstream_node)
+
+    unmarked_nodes = [(node, 0) for node in downstream_nodes]
     while unmarked_nodes:
-        visit(unmarked_nodes.pop(), None)
-    return sorted_nodes, child_map
+        upstream_node, upstream_label = unmarked_nodes.pop()
+        visit(upstream_node, upstream_label, None, None)
+    return sorted_nodes, outgoing_edge_maps
diff --git a/ffmpeg/nodes.py b/ffmpeg/nodes.py
index 0d00437..67415f8 100644
--- a/ffmpeg/nodes.py
+++ b/ffmpeg/nodes.py
@@ -13,11 +13,6 @@ class Node(KwargReprNode):
             incoming_edge_map[downstream_label] = (upstream_node, upstream_label)
         super(Node, self).__init__(incoming_edge_map, name, args, kwargs)
 
-    @property
-    def _parents(self):
-        # TODO: change graph compilation to use `self.incoming_edges` instead.
-        return [edge.upstream_node for edge in self.incoming_edges]
-
 
 class InputNode(Node):
     """InputNode type"""