From dc3efec379dfe55fc8086eed53a36532ebe325c4 Mon Sep 17 00:00:00 2001
From: Claudiu Popa <cpopa@cloudbasesolutions.com>
Date: Tue, 1 Sep 2015 13:19:32 +0300
Subject: [PATCH] Add a version filtering strategy

The current patch proposes the addition of a new data source strategy
for filtering the strategies by a given list of versions.

Each data source exports a new API, called ``version()``, which should
return the underlying version of the said data source. This implies that
each data source module can export multiple versioned data sources and it's
the duty of an external strategy to select the appropiate data source with
regard to a particular set of versions.

Change-Id: I6ef2fdd6520a53fc600232247f23bd22b848461e
---
 cloudinit/sources/base.py                |  4 +++
 cloudinit/sources/openstack/base.py      |  4 +++
 cloudinit/sources/strategy.py            | 19 +++++++++++++
 cloudinit/tests/sources/test_strategy.py | 35 ++++++++++++++++++++++++
 4 files changed, 62 insertions(+)

diff --git a/cloudinit/sources/base.py b/cloudinit/sources/base.py
index 8453f5c4..65f58538 100644
--- a/cloudinit/sources/base.py
+++ b/cloudinit/sources/base.py
@@ -140,6 +140,10 @@ class BaseDataSource(object):
         This should return an instance of :class:`APIResponse`.
         """
 
+    @abc.abstractmethod
+    def version(self):
+        """Get the version of the current data source."""
+
     def instance_id(self):
         """Get this instance's id."""
 
diff --git a/cloudinit/sources/openstack/base.py b/cloudinit/sources/openstack/base.py
index 6b44f5b7..01f59a38 100644
--- a/cloudinit/sources/openstack/base.py
+++ b/cloudinit/sources/openstack/base.py
@@ -50,6 +50,10 @@ class BaseOpenStackSource(base.BaseDataSource):
     def _path_join(self, path, *addons):
         """Join one or more components together."""
 
+    def version(self):
+        """Get the underlying data source version."""
+        return self._version
+
     def _working_version(self):
         versions = self._available_versions()
         # OS_VERSIONS is stored in chronological order, so
diff --git a/cloudinit/sources/strategy.py b/cloudinit/sources/strategy.py
index 32a9b66c..547f8b61 100644
--- a/cloudinit/sources/strategy.py
+++ b/cloudinit/sources/strategy.py
@@ -77,3 +77,22 @@ class SerialSearchStrategy(BaseSearchStrategy):
         for data_source in data_sources:
             if self.is_datasource_available(data_source):
                 yield data_source
+
+
+class FilterVersionStrategy(BaseSearchStrategy):
+    """A strategy for filtering data sources by their version
+
+    :param versions:
+        A list of strings, where each strings is a possible
+        version that a data source can have.
+    """
+
+    def __init__(self, versions=None):
+        if versions is None:
+            versions = []
+        self._versions = versions
+        super(FilterVersionStrategy, self).__init__()
+
+    def search_data_sources(self, data_sources):
+        return (source for source in data_sources
+                if source.version() in self._versions)
diff --git a/cloudinit/tests/sources/test_strategy.py b/cloudinit/tests/sources/test_strategy.py
index fa1b0314..9d84a0bc 100644
--- a/cloudinit/tests/sources/test_strategy.py
+++ b/cloudinit/tests/sources/test_strategy.py
@@ -63,3 +63,38 @@ class TestStrategy(tests.TestCase):
             valid_sources = list(instance.search_data_sources(sources))
 
         self.assertEqual(available_sources, valid_sources)
+
+    def test_filter_version_strategy(self):
+        class SourceV1(object):
+            def version(self):
+                return 'first'
+
+        class SourceV2(SourceV1):
+            def version(self):
+                return 'second'
+
+        class SourceV3(object):
+            def version(self):
+                return 'third'
+
+        sources = [SourceV1(), SourceV2(), SourceV3()]
+        instance = strategy.FilterVersionStrategy(['third', 'first'])
+
+        filtered_sources = sorted(
+            source.version()
+            for source in instance.search_data_sources(sources))
+
+        self.assertEqual(len(filtered_sources), 2)
+        self.assertEqual(filtered_sources, ['first', 'third'])
+
+    def test_filter_version_strategy_no_versions_given(self):
+        class SourceV1(object):
+            def version(self):
+                return 'first'
+
+        sources = [SourceV1()]
+        instance = strategy.FilterVersionStrategy()
+
+        filtered_sources = list(instance.search_data_sources(sources))
+
+        self.assertEqual(len(filtered_sources), 0)