1 files changed, 126 insertions, 0 deletions
diff --git a/lib/git/async/graph.py b/lib/git/async/graph.py
new file mode 100644
index 00000000..4e14c81e
--- /dev/null
+++ b/lib/git/async/graph.py
@@ -0,0 +1,126 @@
+"""Simplistic implementation of a graph"""
+
+__all__ = ('Node', 'Graph')
+
+class Node(object):
+	"""A Node in the graph. They know their neighbours, and have an id which should 
+	resolve into a string"""
+	__slots__ = ('in_nodes', 'out_nodes', 'id')
+	
+	def __init__(self, id=None):
+		self.id = id
+		self.in_nodes = list()
+		self.out_nodes = list()
+		
+	def __str__(self):
+		return str(self.id)
+		
+	def __repr__(self):
+		return "%s(%s)" % (type(self).__name__, self.id)
+	
+	
+class Graph(object):
+	"""A simple graph implementation, keeping nodes and providing basic access and 
+	editing functions. The performance is only suitable for small graphs of not 
+	more than 10 nodes !"""
+	__slots__ = "nodes"
+	
+	def __init__(self):
+		self.nodes = list()
+
+	def __del__(self):
+		"""Deletes bidericational dependencies"""
+		for node in self.nodes:
+			node.in_nodes = None
+			node.out_nodes = None
+		# END cleanup nodes
+		
+		# otherwise the nodes would keep floating around
+	
+
+	def add_node(self, node):
+		"""Add a new node to the graph
+		:return: the newly added node"""
+		self.nodes.append(node)
+		return node
+	
+	def remove_node(self, node):
+		"""Delete a node from the graph
+		:return: self"""
+		try:
+			del(self.nodes[self.nodes.index(node)])
+		except ValueError:
+			return self
+		# END ignore if it doesn't exist
+		
+		# clear connections
+		for outn in node.out_nodes:
+			del(outn.in_nodes[outn.in_nodes.index(node)])
+		for inn in node.in_nodes:
+			del(inn.out_nodes[inn.out_nodes.index(node)])
+		node.out_nodes = list()
+		node.in_nodes = list()
+		return self
+	
+	def add_edge(self, u, v):
+		"""Add an undirected edge between the given nodes u and v.
+		
+		return: self
+		:raise ValueError: If the new edge would create a cycle"""
+		if u is v:
+			raise ValueError("Cannot connect a node with itself")
+		
+		# are they already connected ?
+		if 	u in v.in_nodes and v in u.out_nodes or \
+			v in u.in_nodes and u in v.out_nodes:
+			return self
+		# END handle connection exists
+		
+		# cycle check - if we can reach any of the two by following either ones 
+		# history, its a cycle
+		for start, end in ((u, v), (v,u)):
+			if not start.in_nodes: 
+				continue
+			nodes = start.in_nodes[:]
+			seen = set()
+			# depth first search - its faster
+			while nodes:
+				n = nodes.pop()
+				if n in seen:
+					continue
+				seen.add(n)
+				if n is end:
+					raise ValueError("Connecting u with v would create a cycle")
+				nodes.extend(n.in_nodes)
+			# END while we are searching
+		# END for each direction to look
+		
+		# connection is valid, set it up
+		u.out_nodes.append(v)
+		v.in_nodes.append(u)
+		
+		return self
+	
+	def input_inclusive_dfirst_reversed(self, node):
+		"""Return all input nodes of the given node, depth first,
+		It will return the actual input node last, as it is required
+		like that by the pool"""
+		stack = [node]
+		seen = set()
+		
+		# depth first
+		out = list()
+		while stack:
+			n = stack.pop()
+			if n in seen:
+				continue
+			seen.add(n)
+			out.append(n)
+			
+			# only proceed in that direction if visitor is fine with it
+			stack.extend(n.in_nodes)
+			# END call visitor
+		# END while walking
+		out.reverse()
+		return out
+