config: Add ConfigValue base class and tests.

mopidy/utils/config.py

@@ -17,3 +17,56 @@ def validate_maximum(value, maximum):
     """Maximum validation, normally called in config value's validate()."""
     if maximum is not None and value > maximum:
         raise ValueError('must be smaller than %s.' % maximum)
+
+
+class ConfigValue(object):
+    """Represents a config key's value and how to handle it.
+
+    Normally you will only be interacting with sub-classes for config values
+    that encode either deserialization behavior and/or validation.
+
+    Each config value should be used for the following actions:
+
+    1. Deserializing from a raw string and validating, raising ValueError on
+       failure.
+    2. Serializing a value back to a string that can be stored in a config.
+    3. Formatting a value to a printable form (useful for masking secrets).
+
+    :class:`None` values should not be deserialized, serialized or formatted,
+    the code interacting with the config should simply skip None config values.
+    """
+
+    #: Collection of valid choices for converted value. Must be combined with
+    #: :function:`validate_choices` in :method:`validate` do any thing.
+    choices = None
+
+    #: Minimum of converted value. Must be combined with
+    #: :function:`validate_minimum` in :method:`validate` do any thing.
+    minimum = None
+
+    #: Maximum of converted value. Must be combined with
+    #: :function:`validate_maximum` in :method:`validate` do any thing.
+    maximum = None
+
+    #: Indicate if we should mask the when printing for human consumption.
+    secret = None
+
+    def __init__(self, choices=None, minimum=None, maximum=None, secret=None):
+        self.choices = choices
+        self.minimum = minimum
+        self.maximum = maximum
+        self.secret = secret
+
+    def deserialize(self, value):
+        """Cast raw string to appropriate type."""
+        return value
+
+    def serialize(self, value):
+        """Convert value back to string for saving."""
+        return str(value)
+
+    def format(self, value):
+        """Format value for display."""
+        if self.secret:
+            return '********'
+        return self.serialize(value)

tests/utils/config_test.py

@@ -51,3 +51,38 @@ class ValidateMaximumTest(unittest.TestCase):
     def test_to_large_value_fails_with_zero_as_maximum(self):
         with self.assertRaises(ValueError):
             config.validate_maximum(5, 0)
+
+
+class ConfigValueTest(unittest.TestCase):
+    def test_init(self):
+        value = config.ConfigValue()
+        self.assertIsNone(value.choices)
+        self.assertIsNone(value.minimum)
+        self.assertIsNone(value.maximum)
+        self.assertIsNone(value.secret)
+
+    def test_init_with_params(self):
+        value = config.ConfigValue(
+            choices=['foo'], minimum=0, maximum=10, secret=True)
+        self.assertEqual(['foo'], value.choices)
+        self.assertEqual(0, value.minimum)
+        self.assertEqual(10, value.maximum)
+        self.assertEqual(True, value.secret)
+
+    def test_deserialize_passes_through(self):
+        value = config.ConfigValue()
+        obj = object()
+        self.assertEqual(obj, value.deserialize(obj))
+
+    def test_serialize_converts_to_string(self):
+        value = config.ConfigValue()
+        self.assertIsInstance(value.serialize(object()), basestring)
+
+    def test_format_uses_serialize(self):
+        value = config.ConfigValue()
+        obj = object()
+        self.assertEqual(value.serialize(obj), value.format(obj))
+
+    def test_format_masks_secrets(self):
+        value = config.ConfigValue(secret=True)
+        self.assertEqual('********', value.format(object()))