From 6eb606bb61b46be4745e2c79904fdc212365449d Mon Sep 17 00:00:00 2001
From: Jan Pokorný <jpokorny@redhat.com>
Date: May 25 2017 17:00:01 +0000
Subject: command: factor "common_protocols" out as a class method of Format


Signed-off-by: Jan Pokorný <jpokorny@redhat.com>

---

diff --git a/command.py b/command.py
index d1048d1..1330bef 100644
--- a/command.py
+++ b/command.py
@@ -6,7 +6,6 @@
 __author__ = "Jan Pokorný <jpokorny @at@ Red Hat .dot. com>"
 
 from collections import MutableMapping
-from functools import reduce
 try:
     from itertools import zip_longest
 except ImportError:  # PY2 backward compatibility
@@ -205,26 +204,17 @@ class _Command(object):
                         "filter `{0}' is feeded by `{1}' more than once",
                         i.__class__.__name__, pass_through.__class__.__name__
                     )
-                common_protocols = None  # for when CompositeFormat involved
+                com = None  # for when CompositeFormat involved
                 if (hasattr(pass_through.out_format, '_protocols')
-                    and hasattr(i.in_format, '_protocols')):
-                    common_protocols = sorted(
-                        reduce(
-                            set.intersection,
-                            map(set, (pass_through.out_format._protocols,
-                                    i.in_format._protocols))
-                        ),
-                        key=lambda x:
-                            int(x == pass_through.out_format.native_protocol)
-                            + int(x == i.in_format.native_protocol)
-                    )
-                    if not common_protocols:
+                        and hasattr(i.in_format, '_protocols')):
+                    com = pass_through.out_format.common_protocols(i.in_format)
+                    if not com:
                         raise CommandError(me,
                             "filter `{0}' and its feeder `{1}' have no protocol"
                             " in common",
                             i.__class__.__name__, pass_through.__class__.__name__
                         )
-                bt[pass_through] = common_protocols
+                bt[pass_through] = com
             if i_tail:
                 # PASSDOWN
                 # this uses a dirty trick of exploiting the end of the list
diff --git a/format.py b/format.py
index 2198244..55e1846 100644
--- a/format.py
+++ b/format.py
@@ -245,6 +245,23 @@ class _Format(object):
             setattr(self, attr, get_protocol_proxy(getattr(self, attr)))
         self._swallow(protocol, *args)
 
+    @MimicMeta.passdeco(classmethod)
+    def common_protocols(cls, foreign):
+        """Get common local vs. foreign protocols, native ones prioritized"""
+        # XXX composite format
+        if not hasattr(foreign, '_protocols'):
+            raise FormatError(cls, "cannot check common protocols for `{0}'",
+                              repr(foreign))
+        return sorted(
+            reduce(
+                set.intersection,
+                map(set, (cls._protocols, foreign._protocols))
+            ),
+            key=lambda x:
+                int(x == cls.native_protocol) * 2
+                + int(x == foreign.native_protocol)
+        )
+
     @MimicMeta.classmethod
     def as_instance(cls, *decl_or_instance, **kwargs):
         """Create an instance or verify and return existing one"""