# Source code for mopidy.config.schemas

    import collections

    from mopidy.config import types

    def _did_you_mean(name, choices):
        """Suggest most likely setting based on levenshtein."""
        if not choices:
            return None

        name = name.lower()
        candidates = [(_levenshtein(name, c), c) for c in choices]
        candidates.sort()

        if candidates[0][0] <= 3:
            return candidates[0][1]
        return None

    def _levenshtein(a, b):
        """Calculates the Levenshtein distance between a and b."""
        n, m = len(a), len(b)
        if n > m:
            return _levenshtein(b, a)

        current = range(n + 1)
        for i in range(1, m + 1):
            previous, current = current, [i] + [0] * n
            for j in range(1, n + 1):
                add, delete = previous[j] + 1, current[j - 1] + 1
                change = previous[j - 1]
                if a[j - 1] != b[i - 1]:
                    change += 1
                current[j] = min(add, delete, change)
        return current[n]

    class ConfigSchema(collections.OrderedDict):

        """Logical group of config values that correspond to a config section.

        Schemas are set up by assigning config keys with config values to
        instances. Once setup :meth:`deserialize` can be called with a dict of
        values to process. For convienience we also support :meth:`format` method
        that can used for converting the values to a dict that can be printed and
        :meth:`serialize` for converting the values to a form suitable for
        persistence.
        """

        def __init__(self, name):
            super().__init__()
            self.name = name

        def deserialize(self, values):
            """Validates the given ``values`` using the config schema.

            Returns a tuple with cleaned values and errors.
            """
            errors = {}
            result = {}

            for key, value in values.items():
                try:
                    result[key] = self[key].deserialize(value)
                except KeyError:  # not in our schema
                    errors[key] = "unknown config key."
                    suggestion = _did_you_mean(key, self.keys())
                    if suggestion:
                        errors[key] += f" Did you mean {suggestion!r}?"
                except ValueError as e:  # deserialization failed
                    result[key] = None
                    errors[key] = str(e)

            for key in self.keys():
                if isinstance(self[key], types.Deprecated):
                    result.pop(key, None)
                elif key not in result and key not in errors:
                    result[key] = None
                    errors[key] = "config key not found."

            return result, errors

        def serialize(self, values, display=False):
            """Converts the given ``values`` to a format suitable for persistence.

            If ``display`` is :class:`True` secret config values, like passwords,
            will be masked out.

            Returns a dict of config keys and values."""
            result = collections.OrderedDict()
            for key in self.keys():
                if key in values:
                    result[key] = self[key].serialize(values[key], display)
            return result

    class MapConfigSchema:

        """Schema for handling multiple unknown keys with the same type.

        Does not sub-class :class:`ConfigSchema`, but implements the same
        serialize/deserialize interface.
        """

        def __init__(self, name, value_type):
            self.name = name
            self._value_type = value_type

        def deserialize(self, values):
            errors = {}
            result = {}

            for key, value in values.items():
                try:
                    result[key] = self._value_type.deserialize(value)
                except ValueError as e:  # deserialization failed
                    result[key] = None
                    errors[key] = str(e)
            return result, errors

        def serialize(self, values, display=False):
            result = collections.OrderedDict()
            for key in sorted(values.keys()):
                result[key] = self._value_type.serialize(values[key], display)
            return result