morphlib.artifactcachereference: store basename

This is not to make it easier, but to make it not miss if the algorithm
for generating cache names changes.

Strictly speaking it should store the format string for accessing metadata
as well to be compatible, but missing an artifact's metadata is less important.

1 files changed, 13 insertions, 15 deletions

diff --git a/morphlib/artifactcachereference.py b/morphlib/artifactcachereference.py
index 4cc73290..d4b239d5 100644
--- a/morphlib/artifactcachereference.py
+++ b/morphlib/artifactcachereference.py
@@ -18,26 +18,24 @@ class ArtifactCacheReference(object):
     '''Represent the information needed to retrieve an artifact
 
     The artifact cache doesn't need to know the dependencies or the
-    morphology of an artifact, it just needs to know the cache key,
-    name and kind.
+    morphology of an artifact, it just needs to know the basename
+
+    The basename could be generated, from the name, cache_key and kind,
+    but if the algorithm changes then morph wouldn't be able to find
+    old artifacts with a saved ArtifactCacheReference.
+
+    Conversely if it generated the basename then old strata wouldn't be
+    able to refer to new chunks, but strata change more often than the chunks.
     '''
-    def __init__(self, name, cache_key, kind):
-        self.name = name
-        self.cache_key = cache_key
-        self.kind = kind
+    def __init__(self, basename):
+        self._basename = basename
 
     def basename(self):
-        return '%s.%s.%s' % (self.cache_key,
-                             self.kind,
-                             self.name)
+        return self._basename
 
     def metadata_basename(self, metadata_name):
-        return '%s.%s.%s.%s' % (self.cache_key,
-                                self.kind,
-                                self.name,
-                                metadata_name)
+        return '%s.%s' % (self._basename, metadata_name)
 
     @classmethod
     def from_artifact(klass, artifact):
-        return klass(artifact.name, artifact.cache_key,
-                     artifact.source.morphology['kind'])
+        return klass(artifact.basename())