From d9294d2ff9ca5f42cc81bf3ee36fac3286e1897e Mon Sep 17 00:00:00 2001
From: Stephen Diehl <stephen.m.diehl@gmail.com>
Date: Thu, 26 Apr 2012 21:21:57 -0400
Subject: [PATCH] Base class for transitions.

---
 zipline/transitions.py | 87 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 87 insertions(+)
 create mode 100644 zipline/transitions.py

diff --git a/zipline/transitions.py b/zipline/transitions.py
new file mode 100644
index 00000000..9a68926f
--- /dev/null
+++ b/zipline/transitions.py
@@ -0,0 +1,87 @@
+import types
+from collections import Container, Hashable, Callable
+
+class Any(object): pass
+
+class Workflow(Container, Callable):
+
+    def __init__(self, states, transitions, initial_state):
+        self.simple = set()
+        self.complx = []
+
+        if isinstance(states[0], tuple):
+            self.groups = {b for _,b in states}
+        else:
+            self.groups = set()
+
+        matcher = lambda b: lambda f,t : t == b
+
+        for (a, b) in transitions.itervalues():
+            if a is Any:
+                self.complx.append(matcher(b))
+            if isinstance(a, Hashable) and isinstance(b, Hashable):
+                self.simple.add((a,b))
+
+    def __call__(self, **kwargs):
+        if 'group' in kwargs:
+            return self.groups
+
+    def __contains__(self, state):
+        if state in self.simple:
+            return True
+        for match in self.complx:
+            if match(*state):
+                return True
+        else:
+            return False
+
+class Flowable:
+
+    @property
+    def state(self):
+        if not hasattr(self, '_state'):
+            self._state = self.initial_state
+        else:
+            return self._state
+
+    @state.setter
+    def state(self, new):
+        if not hasattr(self, '_state'):
+            self._state = self.initial_state
+
+        old = self._state
+
+        if (old, new) in self.workflow:
+            self._state = new
+        else:
+            raise RuntimeError("Invalid State Transition : %s -> %s" %(old, new))
+
+class WorkflowMeta(type):
+    """
+    Base metaclass component workflows.
+    """
+
+    def __new__(cls, name, mro, attrs):
+
+        state         = attrs.get('states', None)
+        transitions   = attrs.get('transitions', None)
+        initial_state = attrs.get('initial_state', None)
+
+        if attrs.get('workflow'):
+            raise RuntimeError('`workflow` is a reserved attribute.')
+
+        if not state:
+            raise RuntimeError('Must specify states')
+
+        if not transitions:
+            raise RuntimeError('Must specify transitions')
+
+        if not transitions:
+            raise RuntimeError('Must specify initial_state')
+
+        new_class = super(WorkflowMeta, cls).__new__(
+            cls, name, mro+(Flowable,), attrs
+        )
+        new_class.workflow = Workflow(state, transitions, initial_state)
+
+        return new_class