From e5ac938486edd6edf3b0ec21b14cb16cf095debd Mon Sep 17 00:00:00 2001
From: Isis Lovecruft <isis@leap.se>
Date: Sat, 11 May 2013 18:30:22 +0000
Subject: [PATCH] Add hastily written check_preferences().

 * TODO I sleepily realised two lines before the end of bashing this out that
   it should just be a set difference.
---
 gnupg/parsers.py | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/gnupg/parsers.py b/gnupg/parsers.py
index 3707191..ab10a0c 100644
--- a/gnupg/parsers.py
+++ b/gnupg/parsers.py
@@ -44,6 +44,33 @@ class UsageError(Exception):
     """Raised when incorrect usage of the API occurs.."""
 
 
+def _check_preferences(prefs, pref_type=None):
+    cipher   = frozenset(['AES256', 'AES192', 'CAMELLIA256', 'CAMELLIA192',
+                         'TWOFISH',])
+    digest   = frozenset(['SHA512', 'SHA384', 'SHA256', 'SHA224'])
+    compress = frozenset(['ZLIB', 'ZIP', 'Uncompressed'])
+    all      = frozenset([ciphers, hashes, compress])
+
+    if isinstance(prefs, str):
+        prefs = prefs.split(' ')
+    if not pref_type:
+        pref_type = all
+
+    ## xxx we should use set differences
+    if pref_type == 'cipher':
+        for pref in prefs:
+            if not cipher.contains(pref): return
+    if pref_type == 'digest':
+        for pref in prefs:
+            if not digest.contains(pref): return
+    if pref_type == 'compress':
+        for pref in prefs:
+            if not compress.contains(pref): return
+    if pref_type == 'all':
+        for pref in prefs:
+            if not all.contains(pref): return
+    return ' '.join([pref for pref in prefs])
+
 def _fix_unsafe(shell_input):
     """Find characters used to escape from a string into a shell, and wrap them
     in quotes if they exist. Regex pilfered from python-3.x shlex module.