"""

Module for abstract serializer/unserializer base classes.

"""

from StringIO import StringIO

from django.db import models

from django.utils.encoding import smart_str, smart_unicode

from django.utils import datetime_safe

class SerializationError(Exception):

    """Something bad happened during serialization."""

    pass

class DeserializationError(Exception):

    """Something bad happened during deserialization."""

    pass

class Serializer(object):

    """

    Abstract serializer base class.

    """

    # Indicates if the implemented serializer is only available for

    # internal Django use.

    internal_use_only = False

    def serialize(self, queryset, **options):

        """

        Serialize a queryset.

        """

        self.options = options

        self.stream = options.get("stream", StringIO())

        self.selected_fields = options.get("fields")

        self.start_serialization()

        for obj in queryset:

            self.start_object(obj)

            for field in obj._meta.local_fields:

                if field.serialize:

                    if field.rel is None:

                        if self.selected_fields is None or field.attname in self.selected_fields:

                            self.handle_field(obj, field)

                    else:

                        if self.selected_fields is None or field.attname[:-3] in self.selected_fields:

                            self.handle_fk_field(obj, field)

            for field in obj._meta.many_to_many:

                if field.serialize:

                    if self.selected_fields is None or field.attname in self.selected_fields:

                        self.handle_m2m_field(obj, field)

            self.end_object(obj)

        self.end_serialization()

        return self.getvalue()

    def get_string_value(self, obj, field):

        """

        Convert a field's value to a string.

        """

        return smart_unicode(field.value_to_string(obj))

    def start_serialization(self):

        """

        Called when serializing of the queryset starts.

        """

        raise NotImplementedError

    def end_serialization(self):

        """

        Called when serializing of the queryset ends.

        """

        pass

    def start_object(self, obj):

        """

        Called when serializing of an object starts.

        """

        raise NotImplementedError

    def end_object(self, obj):

        """

        Called when serializing of an object ends.

        """

        pass

    def handle_field(self, obj, field):

        """

        Called to handle each individual (non-relational) field on an object.

        """

        raise NotImplementedError

    def handle_fk_field(self, obj, field):

        """

        Called to handle a ForeignKey field.

        """

        raise NotImplementedError

    def handle_m2m_field(self, obj, field):

        """

        Called to handle a ManyToManyField.

        """

        raise NotImplementedError

    def getvalue(self):

        """

        Return the fully serialized queryset (or None if the output stream is

        not seekable).

        """

        if callable(getattr(self.stream, 'getvalue', None)):

            return self.stream.getvalue()

class Deserializer(object):

    """

    Abstract base deserializer class.

    """

    def __init__(self, stream_or_string, **options):

        """

        Init this serializer given a stream or a string

        """

        self.options = options

        if isinstance(stream_or_string, basestring):

            self.stream = StringIO(stream_or_string)

        else:

            self.stream = stream_or_string

        # hack to make sure that the models have all been loaded before

        # deserialization starts (otherwise subclass calls to get_model()

        # and friends might fail...)

        models.get_apps()

    def __iter__(self):

        return self

    def next(self):

        """Iteration iterface -- return the next item in the stream"""

        raise NotImplementedError

class DeserializedObject(object):

    """

    A deserialized model.

    Basically a container for holding the pre-saved deserialized data along

    with the many-to-many data saved with the object.

    Call ``save()`` to save the object (with the many-to-many data) to the

    database; call ``save(save_m2m=False)`` to save just the object fields

    (and not touch the many-to-many stuff.)

    """

    def __init__(self, obj, m2m_data=None):

        self.object = obj

        self.m2m_data = m2m_data

    def __repr__(self):

        return "<DeserializedObject: %s>" % smart_str(self.object)

    def save(self, save_m2m=True):

        # Call save on the Model baseclass directly. This bypasses any

        # model-defined save. The save is also forced to be raw.

        # This ensures that the data that is deserialized is literally

        # what came from the file, not post-processed by pre_save/save

        # methods.

        models.Model.save_base(self.object, raw=True)

        if self.m2m_data and save_m2m:

            for accessor_name, object_list in self.m2m_data.items():

                setattr(self.object, accessor_name, object_list)

        # prevent a second (possibly accidental) call to save() from saving

        # the m2m data twice.

        self.m2m_data = None