import base64
import copy
import datetime
import json
try:
    # Python 3
    from collections.abc import Sequence
except ImportError:
    # Python 2.7
    from collections import Sequence

import six


class ModelViolationError(Exception):
    """
    ModelViolationError is raised if the data in the instances is not matching its definition.
    """


class ModelMisuseError(Exception):
    """
    ModelMisuseError is raised if the Model definition is not valid.
    """


class Field(object):
    """
    Field is the base of all supported fields.
    """
    @property
    def help(self):
        """
        :return: Documentation help string defining what the field is about.
        """
        return self._help or 'No documentation provided for this field `{}`'.format(type(self).__name__)

    def as_nullable(self):
        """
        Set object` "_nullable_" field to True and return the object back
        """
        self._nullable = True
        return self

    def __init__(self, default=None, help=None):  # noqa; pylint: disable=redefined-builtin
        """
        :param default: Default value to be used if the field is not set
        :param help: Documentation string for generating model documentation
        :type help: str
        """
        self._help = help
        self._nullable = False
        self._default = default

        if type(self) is Field:
            raise ModelMisuseError("Do not use this type directly.")

    def _validate_model_value(self, value, name):
        """
        Validates the value in the Model representation

        :param value: Value to be checked
        :param name: Name of the field (used for a better error reporting only)
        :return: None
        """
        if value is None and not self._nullable:
            raise ModelViolationError('The value of "{name}" field is None, but this is not allowed'.format(name=name))

    def _validate_builtin_value(self, value, name):
        """
        Validates the value in the builtin representation

        :param value: Value to be checked
        :param name: Name of the field (used for a better error reporting only)
        :return: None
        """
        if value is None and not self._nullable:
            raise ModelViolationError('The value of "{name}" field is None, but this is not allowed'.format(name=name))

    def _convert_to_model(self, value, name):
        """
        Performs the conversion from a builtin type to the model representation

        :param value: Value to convert
        :param name: Name of the field (used for a better error reporting only)
        :return: Converted value in the model format
        """
        self._validate_builtin_value(value=value, name=name)
        return value

    def _convert_from_model(self, value, name):
        """
        Performs the conversion from a model type to the builtin representation

        :param value: Value to convert
        :param name: Name of the field (used for a better error reporting only)
        :return: Converted value in the builtin format
        """
        self._validate_model_value(value=value, name=name)
        return value

    def from_initialization(self, source, name, target):
        """
        Assigns the value to the target model passed through during the model initialization

        :param source: Dictionary to extract the value from (usually kwargs)
        :type source: dict
        :param name: Name of the field (used for a better error reporting only)
        :type name: str
        :param target: Target model instance
        :type target: Instance of a Model derived class
        :return: None
        """
        # copy the default value for it not to be shared with other
        # instances of the same model
        source_value = copy.copy(source.get(name, self._default))
        self._validate_model_value(value=source_value, name=name)
        setattr(target, name, source_value)

    def to_model(self, source, name, target):
        """
        Converts the value with the given name to the model representation and assigns the attribute

        :param source: Dictionary to extract the value from
        :type source: dict
        :param name: Name of the field (used for a better error reporting only)
        :type name: str
        :param target: Target model instance
        :type target: Instance of a Model derived class
        :return: None
        """
        # copy the default value for it not to be shared with other
        # instances of the same model
        source_value = copy.copy(source.get(name, self._default))
        if source_value is not None:
            source_value = self._convert_to_model(source_value, name=name)
        self._validate_model_value(value=source_value, name=name)
        setattr(target, name, source_value)

    def to_builtin(self, source, name, target):
        """
        Converts the value with the given name to the builtin representation and assigns the field

        :param source: Source model to get the value from
        :type source: Instance of a Model derived class
        :param name: Name of the field (used for a better error reporting only)
        :type name: str
        :param target: Dictionary to set the value to
        :type target: dict
        :return: None
        """
        target[name] = self._convert_from_model(getattr(source, name, None), name=name)

    def serialize(self):
        """
        :return: Serialized form of the field
        """
        return {
            'nullable': self._nullable,
            'class_name': type(self).__name__,
            'default': self._default,
            'help': self._help
        }


class BuiltinField(Field):
    """
    Base class for all builtin types to act as pass-through with an additional validation
    """

    @property
    def _model_type(self):
        """
        :return: Returns the type to be used as a model type representation
        """
        raise NotImplementedError("_model_type needs to be overridden")

    @property
    def _builtin_type(self):
        """
        :return: Returns the type to be used as a builtin type representation (e.g. string)
        """
        return self._model_type

    def _validate_model_value(self, value, name):
        super(BuiltinField, self)._validate_model_value(value, name)
        self._validate(value=value, name=name, expected_type=self._model_type)

    def _validate_builtin_value(self, value, name):
        super(BuiltinField, self)._validate_builtin_value(value, name)
        self._validate(value=value, name=name, expected_type=self._builtin_type)

    def _validate(self, value, name, expected_type):
        if not isinstance(expected_type, Sequence):
            expected_type = (expected_type,)

        if value is None and self._nullable:
            return

        if not isinstance(value, expected_type):
            names = ', '.join(['{}'.format(t.__name__) for t in expected_type])
            raise ModelViolationError("Fields {} is of type: {} expected: {}".format(name, type(value).__name__,
                                                                                     names))


class Boolean(BuiltinField):
    """
    Boolean field
    """
    @property
    def _model_type(self):
        return bool


class Float(BuiltinField):
    """
    Float field
    """
    @property
    def _model_type(self):
        return float


class Integer(BuiltinField):
    """
    Integer field (int, long in python 2, int in python 3)
    """
    @property
    def _model_type(self):
        return six.integer_types


class Number(BuiltinField):
    """
    Combined Integer and Float field
    """
    @property
    def _model_type(self):
        return six.integer_types + (float,)


class String(BuiltinField):
    """
    String field
    """
    @property
    def _model_type(self):
        return six.string_types + (six.binary_type,)


class Blob(BuiltinField):
    """
    Blob field
    """
    @property
    def _model_type(self):
        # NOTE(ivasilev) Both string_types and binary_types are necessary here to pass value checks on
        # serialization/deserialization. Serialized JSON-friendly model will have a string type field (the base64
        # ascii string) while deserialized model will have a binary type field.
        return six.string_types + (six.binary_type,)

    def _convert_to_model(self, value, name):
        self._validate_model_value(value=value, name=name)
        if value is None:
            return None

        return base64.b64decode(value)

    def _convert_from_model(self, value, name):
        self._validate_model_value(value=value, name=name)
        if value is None:
            return None

        # NOTE(ivasilev) b64 encoding is always ascii, thus ascii decoding to get a string
        return base64.b64encode(value).decode('ascii')


class DateTime(BuiltinField):
    """
    DateTime field to handle datetime objects which are converted to the ISO format and parsed back from there
    """
    @property
    def _model_type(self):
        return datetime.datetime

    @property
    def _builtin_type(self):
        return six.string_types

    def _convert_to_model(self, value, name):
        self._validate_builtin_value(value=value, name=name)

        if value is None:
            return value

        # We want Z to be appended but it needs support from our side here:
        value = value.rstrip('Z')

        # If there are fractions, use them
        fractions = ''
        if '.' in value:
            fractions = '.%f'

        # Try to parse with timezone specification, else retry without
        try:
            return datetime.datetime.strptime(value, '%Y-%m-%dT%H:%M:%S{fractions}%Z'.format(fractions=fractions))
        except ValueError:
            try:
                return datetime.datetime.strptime(value, '%Y-%m-%dT%H:%M:%S{fractions}'.format(fractions=fractions))
            except ValueError:
                raise ModelViolationError(
                    "The {name} field contains an invalid datetime value: '{value}'".format(name=name, value=value))

    def _convert_from_model(self, value, name):
        self._validate_model_value(value=value, name=name)

        if not value:
            return value

        if not value.utcoffset():
            return value.isoformat() + 'Z'


class EnumMixin(Field):
    """
    EnumMixin adds the ability to use the field as an Enum type of the field
    """
    def __init__(self, choices, **kwargs):
        """
        :param choices: List of values that are allowed for this field
        :type choices: List or tuple of allowed values
        """
        super(EnumMixin, self).__init__(**kwargs)
        if not isinstance(choices, (tuple, list)):
            raise ModelMisuseError("Choices needs to be a list or a tuple")
        self._choices = choices

    def _validate_model_value(self, value, name):
        super(EnumMixin, self)._validate_model_value(value, name)
        self._validate_choices(value, name)

    def _validate_builtin_value(self, value, name):
        super(EnumMixin, self)._validate_builtin_value(value, name)
        self._validate_choices(value, name)

    def _validate_choices(self, value, name):
        if value is not None and value not in self._choices:
            values = ", ".join(map(str, self._choices))
            raise ModelViolationError(
                'The value of "{name}" field must be one of "{values}"'.format(name=name, values=values))

    def serialize(self):
        result = super(EnumMixin, self).serialize()
        result.update({
            'choices': self._choices
        })
        return result


def Nullable(elem_field):
    """
    Helper function to make a field nullable
    """
    return elem_field.as_nullable()


class StringEnum(EnumMixin, String):
    """
    Field that represents an enumeration of Strings
    """


class IntegerEnum(EnumMixin, Integer):
    """
    Field that represents an enumeration of Integers
    """


class FloatEnum(EnumMixin, Float):
    """
    Field that represents an enumeration of Floats
    """


class NumberEnum(EnumMixin, Number):
    """
    Field that represents an enumeration of Numbers
    """


class List(Field):
    """
        List represents lists of `elem_field` values
    """
    def __init__(self, elem_field, minimum=None, maximum=None, **kwargs):
        """
        :param elem_field:
        :type elem: Instance of :py:class:`Field`
        :param minimum: Minimal number of elements
        :type minimum: int or None
        :param maximum: Maximum number of elements
        :type maximum: int or None
        :param default: Default value to use if the field is not set
        :type default: A list of elements with the value type as specified in `elem_field`
        :param help: Documentation string for generating model documentation
        :type help: str
        """
        super(List, self).__init__(**kwargs)
        # We do a copy of the data in default, to avoid some unwanted side effects
        # Comparison to None is necessary
        if self._default is not None:
            self._default = copy.copy(self._default)
        if not isinstance(elem_field, Field):
            raise ModelMisuseError("elem_field must be an instance of a type derived from Field")
        self._elem_type = elem_field
        self._minimum = minimum or 0
        self._maximum = maximum

    def _validate_count(self, value, name):
        message = 'Element count error for field {name} expected between {minimum} and {maximum} elements got {count}'
        count = len(value)
        if not self._minimum <= count <= (self._maximum or count):
            raise ModelViolationError(
                message.format(name=name, minimum=self._minimum, maximum=self._maximum or count, count=count))

    def _validate_model_value(self, value, name):
        super(List, self)._validate_model_value(value, name)
        if isinstance(value, (list, tuple)):
            self._validate_count(value, name)
            for idx, entry in enumerate(value):
                self._elem_type._validate_model_value(entry, name='{}[{}]'.format(name, idx))
        elif value is not None:
            raise ModelViolationError('Expected list but got {} for the {} field'.format(type(value).__name__, name))

    def _validate_builtin_value(self, value, name):
        super(List, self)._validate_builtin_value(value, name)
        if isinstance(value, (list, tuple)):
            self._validate_count(value, name)
            for idx, entry in enumerate(value):
                self._elem_type._validate_builtin_value(entry, name='{}[{}]'.format(name, idx))
        elif value is not None:
            raise ModelViolationError('Expected list but got {} for the {} field'.format(type(value).__name__, name))

    def _convert_to_model(self, value, name):
        self._validate_builtin_value(value=value, name=name)
        if value is None:
            return value
        converter = self._elem_type._convert_to_model
        return list(converter(entry, name='{}[{}]'.format(name, idx)) for idx, entry in enumerate(value))

    def _convert_from_model(self, value, name):
        self._validate_model_value(value=value, name=name)
        if value is None:
            return value
        converter = self._elem_type._convert_from_model
        return list(converter(entry, name='{}[{}]'.format(name, idx)) for idx, entry in enumerate(value))

    def serialize(self):
        result = super(List, self).serialize()
        result.update({
            'element': self._elem_type.serialize(),
            'maximum': self._maximum,
            'minimum': self._minimum
        })
        return result


class StringMap(Field):
    """
    Map from strings to instances of a given value type.
    """
    def __init__(self, value_type, **kwargs):
        super(StringMap, self).__init__(**kwargs)

        if self._default is not None:
            self._default = copy.copy(self._default)

        if not isinstance(value_type, Field):
            raise ModelMisuseError("value_type must be an instance of a type derived from Field")

        self._value_type = value_type

    def _validate_model_value_using_validator(self, new_map, name, validation_method):
        list_validator_fn = getattr(super(StringMap, self), validation_method)
        list_validator_fn(new_map, name)

        if isinstance(new_map, dict):
            for key in new_map:
                # Check that the key is trully a string
                if not isinstance(key, str):
                    err = 'Expected a key of type `str`, but got a key `{}` of type `{}`'
                    raise ModelViolationError(err.format(key, type(key).__name__))

                value = new_map[key]  # avoid using .items(), as it creates a list of all items (slow) in py2

                # _value_type's validation will check whether the value has a correct type
                value_validator_fn = getattr(self._value_type, validation_method)
                value_validator_fn(value, name='{}[{}]'.format(name, key))
        elif value is not None:
            raise ModelViolationError('Expected a dict but got {} for the {} field'.format(type(value).__name__, name))

    def _validate_model_value(self, value, name):
        self._validate_model_value_using_validator(value, name, '_validate_model_value')

    def _validate_builtin_value(self, value, name):
        self._validate_model_value_using_validator(value, name, '_validate_builtin_value')

    def _convert_to_model(self, value, name):
        self._validate_builtin_value(value=value, name=name)

        if value is None:
            return value

        converter = self._value_type._convert_to_model
        return {key: converter(value[key], name='{0}["{1}"]'.format(name, key)) for key in value}

    def _convert_from_model(self, value, name):
        self._validate_model_value(value=value, name=name)

        if value is None:
            return value

        converter = self._value_type._convert_from_model
        return {key: converter(value[key], name='{0}["{1}"]'.format(name, key)) for key in value}

    def serialize(self):
        result = super(StringMap, self).serialize()
        result['value_type'] = self._value_type.serialize()
        return result


class Model(Field):
    """
    Model is used to use other Models as fields
    """
    def __init__(self, model_type, **kwargs):
        """
        :param model_type: A :py:class:`leapp.model.Model` derived class
        :type model_type: :py:class:`leapp.model.Model` derived class
        :param help: Documentation string for generating the model documentation
        :type help: str
        """
        super(Model, self).__init__(**kwargs)
        from leapp.models import Model as ModelType  # pylint: disable=import-outside-toplevel
        if not isinstance(model_type, type) or not issubclass(model_type, ModelType):
            raise ModelMisuseError("{} must be a type derived from Model".format(model_type))
        self._model_type = model_type

    def _validate_model_value(self, value, name):
        super(Model, self)._validate_model_value(value, name)
        resolved_model = getattr(self._model_type, '_resolved', self._model_type)
        if value and not isinstance(value, resolved_model):
            raise ModelViolationError('Expected an instance of {} for the {} attribute but got {}'.format(
                resolved_model.__name__, name, type(value)))

    def _validate_builtin_value(self, value, name):
        super(Model, self)._validate_model_value(value, name)
        if value and not isinstance(value, dict):
            raise ModelViolationError('Expected a value for the {} field and got {}'.format(name, type(value).__name__))

    def _convert_to_model(self, value, name):
        self._validate_builtin_value(value, name)
        if value is None:
            return value
        return self._model_type(init_method='to_model', **value)

    def _convert_from_model(self, value, name):
        self._validate_model_value(value, name)
        if value is None:
            return value
        return value.dump()

    def serialize(self):
        result = super(Model, self).serialize()
        result.update({
            'model': self._model_type.__name__
        })
        return result


class JSON(String):
    """
    The JSON field allows to use json encodable python types as a value.

    The value will be internally encoded to a JSON string and converted back into, whatever the result of json.loads
    is for that value passed.

        Note: The value `None`, however follows the same rules as for all fields and requires the field to be nullable,
              to allow this value. Within nested values such as lists or dicts, a None value is perfectly valid.
    """

    @property
    def _model_type(self):
        return six.integer_types + (float, tuple, dict, list) + six.string_types

    def _convert_from_model(self, value, name):
        if value is None:
            if not self._nullable:
                raise ModelViolationError(
                    'The value of "{name}" field is None, but this is not allowed'.format(name=name))
            return value
        try:
            return json.dumps(value, sort_keys=True)
        except (TypeError, ValueError):
            raise ModelViolationError('Expected a json encodable value for the field {}'.format(name))

    def _convert_to_model(self, value, name):
        self._validate_builtin_value(value, name)
        if value is None:
            return value
        return json.loads(value)