"""
YAML serializer.

Requires PyYaml (http://pyyaml.org/), but that's checked for in __init__.
"""

import decimal
import yaml
from io import StringIO

from django.db import models
from django.core.serializers.base import DeserializationError
from django.core.serializers.python import Serializer as PythonSerializer
from django.core.serializers.python import Deserializer as PythonDeserializer
from django.utils import six


class DjangoSafeDumper(yaml.SafeDumper):
    def represent_decimal(self, data):
        return self.represent_scalar('tag:yaml.org,2002:str', str(data))

DjangoSafeDumper.add_representer(decimal.Decimal, DjangoSafeDumper.represent_decimal)

class Serializer(PythonSerializer):
    """
    Convert a queryset to YAML.
    """

    internal_use_only = False

    def handle_field(self, obj, field):
        # A nasty special case: base YAML doesn't support serialization of time
        # types (as opposed to dates or datetimes, which it does support). Since
        # we want to use the "safe" serializer for better interoperability, we
        # need to do something with those pesky times. Converting 'em to strings
        # isn't perfect, but it's better than a "!!python/time" type which would
        # halt deserialization under any other language.
        if isinstance(field, models.TimeField) and getattr(obj, field.name) is not None:
            self._current[field.name] = str(getattr(obj, field.name))
        else:
            super(Serializer, self).handle_field(obj, field)

    def end_serialization(self):
        yaml.dump(self.objects, self.stream, Dumper=DjangoSafeDumper, **self.options)

    def getvalue(self):
        # Grand-parent super
        return super(PythonSerializer, self).getvalue()

def Deserializer(stream_or_string, **options):
    """
    Deserialize a stream or string of YAML data.
    """
    if isinstance(stream_or_string, bytes):
        stream_or_string = stream_or_string.decode('utf-8')
    if isinstance(stream_or_string, six.string_types):
        stream = StringIO(stream_or_string)
    else:
        stream = stream_or_string
    try:
        for obj in PythonDeserializer(yaml.safe_load(stream), **options):
            yield obj
    except GeneratorExit:
        raise
    except Exception as e:
        # Map to deserializer error
        raise DeserializationError(e)