[click_helper] Implement AliasedGroup.

Implements get_command used for commands aliasing. Use prefix aliasing.

beat/cmdline/scripts/click_helper.py

@@ -10,6 +10,7 @@ try:
 except NameError:
     basestring = str
 
+
 def verbosity_option(**kwargs):
     """Adds a -v/--verbose option to a click command.
 
@@ -37,3 +38,18 @@ def verbosity_option(**kwargs):
             "--verbose option as often as desired (e.g. '-vvv' for debug).",
             callback=callback, **kwargs)(f)
     return custom_verbosity_option
+
+
+class AliasedGroup(click.Group):
+
+    def get_command(self, ctx, cmd_name):
+        rv = click.Group.get_command(self, ctx, cmd_name)
+        if rv is not None:
+            return rv
+        matches = [x for x in self.list_commands(ctx)
+                   if x.startswith(cmd_name)]
+        if not matches:
+            return None
+        elif len(matches) == 1:
+            return click.Group.get_command(self, ctx, matches[0])
+        ctx.fail('Too many matches: %s' % ', '.join(sorted(matches)))