"""

A Python "serializer". Doesn't do much serializing per se -- just converts to

and from basic Python data types (lists, dicts, strings, etc.). Useful as a basis for

other serializers.

"""

from django.conf import settings

from django.core.serializers import base

from django.db import models, DEFAULT_DB_ALIAS

from django.utils.encoding import smart_unicode, is_protected_type

class Serializer(base.Serializer):

    """

    Serializes a QuerySet to basic Python objects.

    """

    internal_use_only = True

    def start_serialization(self):

        self._current = None

        self.objects = []

    def end_serialization(self):

        pass

    def start_object(self, obj):

        self._current = {}

    def end_object(self, obj):

        self.objects.append({

            "model"  : smart_unicode(obj._meta),

            "pk"     : smart_unicode(obj._get_pk_val(), strings_only=True),

            "fields" : self._current

        })

        self._current = None

    def handle_field(self, obj, field):

        value = field._get_val_from_obj(obj)

        # Protected types (i.e., primitives like None, numbers, dates,

        # and Decimals) are passed through as is. All other values are

        # converted to string first.

        if is_protected_type(value):

            self._current[field.name] = value

        else:

            self._current[field.name] = field.value_to_string(obj)

    def handle_fk_field(self, obj, field):

        related = getattr(obj, field.name)

        if related is not None:

            if self.use_natural_keys and hasattr(related, 'natural_key'):

                related = related.natural_key()

            else:

                if field.rel.field_name == related._meta.pk.name:

                    # Related to remote object via primary key

                    related = related._get_pk_val()

                else:

                    # Related to remote object via other field

                    related = smart_unicode(getattr(related, field.rel.field_name), strings_only=True)

        self._current[field.name] = related

    def handle_m2m_field(self, obj, field):

        if field.rel.through._meta.auto_created:

            if self.use_natural_keys and hasattr(field.rel.to, 'natural_key'):

                m2m_value = lambda value: value.natural_key()

            else:

                m2m_value = lambda value: smart_unicode(value._get_pk_val(), strings_only=True)

            self._current[field.name] = [m2m_value(related)

                               for related in getattr(obj, field.name).iterator()]

    def getvalue(self):

        return self.objects

def Deserializer(object_list, **options):

    """

    Deserialize simple Python objects back into Django ORM instances.

    It's expected that you pass the Python objects themselves (instead of a

    stream or a string) to the constructor

    """

    db = options.pop('using', DEFAULT_DB_ALIAS)

    models.get_apps()

    for d in object_list:

        # Look up the model and starting build a dict of data for it.

        Model = _get_model(d["model"])

        data = {Model._meta.pk.attname : Model._meta.pk.to_python(d["pk"])}

        m2m_data = {}

        # Handle each field

        for (field_name, field_value) in d["fields"].iteritems():

            if isinstance(field_value, str):

                field_value = smart_unicode(field_value, options.get("encoding", settings.DEFAULT_CHARSET), strings_only=True)

            field = Model._meta.get_field(field_name)

            # Handle M2M relations

            if field.rel and isinstance(field.rel, models.ManyToManyRel):

                if hasattr(field.rel.to._default_manager, 'get_by_natural_key'):

                    def m2m_convert(value):

                        if hasattr(value, '__iter__'):

                            return field.rel.to._default_manager.db_manager(db).get_by_natural_key(*value).pk

                        else:

                            return smart_unicode(field.rel.to._meta.pk.to_python(value))

                else:

                    m2m_convert = lambda v: smart_unicode(field.rel.to._meta.pk.to_python(v))

                m2m_data[field.name] = [m2m_convert(pk) for pk in field_value]

            # Handle FK fields

            elif field.rel and isinstance(field.rel, models.ManyToOneRel):

                if field_value is not None:

                    if hasattr(field.rel.to._default_manager, 'get_by_natural_key'):

                        if hasattr(field_value, '__iter__'):

                            obj = field.rel.to._default_manager.db_manager(db).get_by_natural_key(*field_value)

                            value = getattr(obj, field.rel.field_name)

                            # If this is a natural foreign key to an object that

                            # has a FK/O2O as the foreign key, use the FK value

                            if field.rel.to._meta.pk.rel:

                                value = value.pk

                        else:

                            value = field.rel.to._meta.get_field(field.rel.field_name).to_python(field_value)

                        data[field.attname] = value

                    else:

                        data[field.attname] = field.rel.to._meta.get_field(field.rel.field_name).to_python(field_value)

                else:

                    data[field.attname] = None

            # Handle all other fields

            else:

                data[field.name] = field.to_python(field_value)

        yield base.DeserializedObject(Model(**data), m2m_data)

def _get_model(model_identifier):

    """

    Helper to look up a model from an "app_label.module_name" string.

    """

    try:

        Model = models.get_model(*model_identifier.split("."))

    except TypeError:

        Model = None

    if Model is None:

        raise base.DeserializationError(u"Invalid model identifier: '%s'" % model_identifier)

    return Model