1 files changed, 78 insertions, 0 deletions
diff --git a/morphlib/definitions_version.py b/morphlib/definitions_version.py
new file mode 100644
index 00000000..44bed178
--- /dev/null
+++ b/morphlib/definitions_version.py
@@ -0,0 +1,78 @@
+# Copyright (C) 2015  Codethink Limited
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; version 2 of the License.
+#
+# 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/>.
+#
+# =*= License: GPL-2 =*=
+
+
+'''Functions for dealing with the definitions VERSION marker file.'''
+
+
+import cliapp
+import yaml
+
+import morphlib
+
+
+SUPPORTED_VERSIONS = [3, 4, 5, 6]
+
+
+class DefinitionsVersionError(cliapp.AppException):
+    pass
+
+
+class UnknownVersionError(DefinitionsVersionError):  # pragma: no cover
+    def __init__(self, version):
+        DefinitionsVersionError.__init__(
+            self, "Definitions format version %s is not supported" % version)
+
+
+class InvalidVersionFileError(DefinitionsVersionError):  # pragma: no cover
+    def __init__(self):
+        DefinitionsVersionError.__init__(self, "invalid VERSION file")
+
+
+def parse_version_file(version_text):
+    '''Parse VERSION file and return the version of the format if:
+
+    VERSION is a YAML file
+    and it's a dict
+    and has the key 'version'
+    and the type stored in the 'version' key is an int
+
+    otherwise returns None
+
+    '''
+    yaml_obj = yaml.safe_load(version_text)
+
+    return (yaml_obj['version'] if yaml_obj is not None
+                                and isinstance(yaml_obj, dict)
+                                and 'version' in yaml_obj
+                                and isinstance(yaml_obj['version'], int)
+
+                                else None)
+
+
+def check_version_file(version_text):  # pragma: no cover
+    '''Check the VERSION information is valid and is a supported version.'''
+
+    if version_text == None:
+        raise InvalidVersionFileError()
+
+    version = morphlib.definitions_version.parse_version_file(version_text)
+
+    if version == None:
+        raise InvalidVersionFileError()
+
+    if version not in SUPPORTED_VERSIONS:
+        raise UnknownVersionError(version)