Add state to dot->svg tool

Add a helper tool that can convert the
allowed state transitions into a dot graph
which itself then converts it into a browser
compatible svg file, which can then be looked
at to have a pretty state diagram.

Change-Id: I3cbbc75bd58182700ddc07f00395da5d1093a26c

taskflow/states.py

@@ -109,7 +109,7 @@ def check_flow_transition(old_state, new_state):
 
     If transition can be performed, it returns True. If transition
     should be ignored, it returns False. If transition is not
-    invalid, it raises InvalidStateException.
+    valid, it raises InvalidStateException.
     """
     if old_state == new_state:
         return False

tools/state_graph.py

@@ -0,0 +1,65 @@
+#!/usr/bin/env python
+
+import os
+import sys
+
+top_dir = os.path.abspath(os.path.join(os.path.dirname(__file__),
+                                       os.pardir))
+sys.path.insert(0, top_dir)
+
+import optparse
+import subprocess
+import tempfile
+
+import networkx as nx
+
+from taskflow import states
+from taskflow.utils import graph_utils as gu
+
+
+def mini_exec(cmd, ok_codes=(0,)):
+    stdout = subprocess.PIPE
+    stderr = subprocess.PIPE
+    proc = subprocess.Popen(cmd, stdout=stdout, stderr=stderr, stdin=None)
+    (stdout, stderr) = proc.communicate()
+    rc = proc.returncode
+    if rc not in ok_codes:
+        raise RuntimeError("Could not run %s [%s]", cmd, rc)
+    return (stdout, stderr)
+
+
+def make_svg(graph, output_filename):
+    # NOTE(harlowja): requires pydot!
+    gdot = gu.export_graph_to_dot(graph)
+    with tempfile.NamedTemporaryFile(suffix=".dot") as fh:
+        fh.write(gdot)
+        fh.flush()
+        cmd = ['dot', '-Tsvg', fh.name]
+        stdout, _stderr = mini_exec(cmd)
+        with open(output_filename, "wb") as fh:
+            fh.write(stdout)
+    # NOTE(harlowja): if u want a png instead u can run the following which
+    # requires ImageMagick and its little helper `convert` program.
+    #
+    # $ convert input.svg output.png
+
+
+def main():
+    parser = optparse.OptionParser()
+    parser.add_option("-f", "--file", dest="filename",
+                      help="write svg to FILE", metavar="FILE",
+                      default="states.svg")
+    (options, args) = parser.parse_args()
+    g = nx.DiGraph(name="State transitions")
+    for (u, v) in states._ALLOWED_FLOW_TRANSITIONS:
+        if not g.has_node(u):
+            g.add_node(u)
+        if not g.has_node(v):
+            g.add_node(v)
+        g.add_edge(u, v)
+    make_svg(g, options.filename)
+    print("Created svg at '%s'" % (options.filename))
+
+
+if __name__ == '__main__':
+    main()