1 files changed, 155 insertions, 0 deletions
diff --git a/cloudinit/mergers/__init__.py b/cloudinit/mergers/__init__.py
new file mode 100644
index 00000000..45e88fb3
--- /dev/null
+++ b/cloudinit/mergers/__init__.py
@@ -0,0 +1,155 @@
+# vi: ts=4 expandtab
+#
+#    Copyright (C) 2012 Yahoo! Inc.
+#
+#    Author: Joshua Harlow <harlowja@yahoo-inc.com>
+#
+#    This program is free software: you can redistribute it and/or modify
+#    it under the terms of the GNU General Public License version 3, as
+#    published by the Free Software Foundation.
+#
+#    This program is distributed in the hope that it will be useful,
+#    but WITHOUT ANY WARRANTY; without even the implied warranty of
+#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+#    GNU General Public License for more details.
+#
+#    You should have received a copy of the GNU General Public License
+#    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+import re
+
+from cloudinit import importer
+from cloudinit import log as logging
+from cloudinit import type_utils
+
+NAME_MTCH = re.compile(r"(^[a-zA-Z_][A-Za-z0-9_]*)\((.*?)\)$")
+
+LOG = logging.getLogger(__name__)
+DEF_MERGE_TYPE = "list(extend)+dict()+str(append)"
+
+
+class UnknownMerger(object):
+    # Named differently so auto-method finding
+    # doesn't pick this up if there is ever a type
+    # named "unknown"
+    def _handle_unknown(self, meth_wanted, value, merge_with):
+        return value
+
+    # This merging will attempt to look for a '_on_X' method
+    # in our own object for a given object Y with type X,
+    # if found it will be called to perform the merge of a source
+    # object and a object to merge_with.
+    #
+    # If not found the merge will be given to a '_handle_unknown'
+    # function which can decide what to do wit the 2 values.
+    def merge(self, source, merge_with):
+        type_name = type_utils.obj_name(source)
+        type_name = type_name.lower()
+        method_name = "_on_%s" % (type_name)
+        meth = None
+        args = [source, merge_with]
+        if hasattr(self, method_name):
+            meth = getattr(self, method_name)
+        if not meth:
+            meth = self._handle_unknown
+            args.insert(0, method_name)
+        return meth(*args)
+
+
+class LookupMerger(UnknownMerger):
+    def __init__(self, lookups=None):
+        UnknownMerger.__init__(self)
+        if lookups is None:
+            self._lookups = []
+        else:
+            self._lookups = lookups
+
+    # For items which can not be merged by the parent this object
+    # will lookup in a internally maintained set of objects and
+    # find which one of those objects can perform the merge. If
+    # any of the contained objects have the needed method, they
+    # will be called to perform the merge.
+    def _handle_unknown(self, meth_wanted, value, merge_with):
+        meth = None
+        for merger in self._lookups:
+            if hasattr(merger, meth_wanted):
+                # First one that has that method/attr gets to be
+                # the one that will be called
+                meth = getattr(merger, meth_wanted)
+                break
+        if not meth:
+            return UnknownMerger._handle_unknown(self, meth_wanted,
+                                                 value, merge_with)
+        return meth(value, merge_with)
+
+
+def dict_extract_mergers(config):
+    parsed_mergers = []
+    raw_mergers = config.get('merge_how')
+    if raw_mergers is None:
+        raw_mergers = config.get('merge_type')
+    if raw_mergers is None:
+        return parsed_mergers
+    if isinstance(raw_mergers, (str, basestring)):
+        return string_extract_mergers(raw_mergers)
+    for m in raw_mergers:
+        if isinstance(m, (dict)):
+            name = m['name']
+            name = name.replace("-", "_").strip()
+            opts = m['settings']
+        else:
+            name = m[0]
+            if len(m) >= 2:
+                opts = m[1:]
+            else:
+                opts = []
+        if name:
+            parsed_mergers.append((name, opts))
+    return parsed_mergers
+
+
+def string_extract_mergers(merge_how):
+    parsed_mergers = []
+    for m_name in merge_how.split("+"):
+        # Canonicalize the name (so that it can be found
+        # even when users alter it in various ways)
+        m_name = m_name.lower().strip()
+        m_name = m_name.replace("-", "_")
+        if not m_name:
+            continue
+        match = NAME_MTCH.match(m_name)
+        if not match:
+            msg = "Matcher identifer '%s' is not in the right format" % (m_name)
+            raise ValueError(msg)
+        (m_name, m_ops) = match.groups()
+        m_ops = m_ops.strip().split(",")
+        m_ops = [m.strip().lower() for m in m_ops if m.strip()]
+        parsed_mergers.append((m_name, m_ops))
+    return parsed_mergers
+
+
+def default_mergers():
+    return tuple(string_extract_mergers(DEF_MERGE_TYPE))
+
+
+def construct(parsed_mergers):
+    mergers_to_be = []
+    for (m_name, m_ops) in parsed_mergers:
+        merger_locs = importer.find_module(m_name,
+                                           [__name__],
+                                           ['Merger'])
+        if not merger_locs:
+            msg = "Could not find merger named '%s'" % (m_name)
+            raise ImportError(msg)
+        else:
+            mod = importer.import_module(merger_locs[0])
+            mod_attr = getattr(mod, 'Merger')
+            mergers_to_be.append((mod_attr, m_ops))
+    # Now form them...
+    mergers = []
+    root = LookupMerger(mergers)
+    for (attr, opts) in mergers_to_be:
+        mergers.append(attr(root, opts))
+    return root
+
+