cli: add dependency graph printing

Introduce a new command 'show-dependencies' that prints producent/
consumer dependencies between all actors in a given workflow in the DOT
format that allows easy visualization.

Author: MichalHe

leapp/snactor/commands/show_dependencies.py

@@ -0,0 +1,66 @@
+import itertools
+from collections import defaultdict
+import datetime
+import sys
+
+from leapp.exceptions import CommandError, LeappError
+from leapp.logger import configure_logger
+from leapp.repository.scan import find_and_scan_repositories
+from leapp.snactor.context import with_snactor_context
+from leapp.utils.clicmd import command, command_arg
+from leapp.utils.repository import find_repository_basedir, requires_repository
+
+_LONG_DESCRIPTION = '''
+Outputs the graph of dependencies between actors formed by producer/consumer their relations in the DOT langauge.
+The DOT language allows easy visualization of the graph.
+'''
+
+
+@command('show-dependencies',
+         help='Print dependency graph of a workflow in the DOT language.',
+         description=_LONG_DESCRIPTION)
+@command_arg('workflow_name')
+@requires_repository
+@with_snactor_context
+def cli(params):
+    start = datetime.datetime.utcnow()
+    configure_logger()
+    repository = find_and_scan_repositories(find_repository_basedir('.'), include_locals=True)
+    try:
+        repository.load()
+    except LeappError as exc:
+        sys.stderr.write(exc.message)
+        sys.stderr.write('\n')
+        sys.exit(1)
+
+    workflow = repository.lookup_workflow(params.workflow_name)
+    if not workflow:
+        raise CommandError('Could not find any workflow named "{}"'.format(params.name))
+
+    workflow_instance = workflow()
+
+    # Information about message consuments and producers:
+    dependency_graph = defaultdict(lambda: {'producers': set(), 'consumers': set()})
+
+    for staged_phase in workflow_instance.phase_actors:
+        # staged_phase = ('name' <str>, 'Before' <PhaseActors>, 'Main' <PhaseActors>, 'After' <PhaseActors>)
+        before_stage, main_stage, after_stage = staged_phase[1:]
+
+        for actor in itertools.chain(before_stage.actors, main_stage.actors, after_stage.actors):
+            for consumed_message in actor.consumes:
+                dependency_graph[consumed_message.__name__]['consumers'].add(actor.name)
+            for produced_message in actor.produces:
+                dependency_graph[produced_message.__name__]['producents'].add(actor.name)
+
+    # Display the dependency graph in the DOT format. We don't want to add dependencies on another library,
+    # so we do the formatting ourselves since its pretty straightforward
+    dot_output_lines = ['digraph LeappDependencyGraph {']
+
+    for message, message_info in dependency_graph.items():
+        for producent, consument in itertools.product(message_info['producents'], message_info['consuments']):
+            output_line = '  "{0}" -> "{1}" [label="{2}"]'.format(producent, consument, message)
+            dot_output_lines.append(output_line)
+
+    dot_output_lines.append('}')
+    dot_output = '\n'.join(dot_output_lines) + '\n'
+    print(dot_output, end='')