from rest_framework.compat import smart_text, urlparse
from rest_framework.fields import get_attribute, empty, Field
from rest_framework.reverse import reverse
from rest_framework.utils import html
from django.core.exceptions import ObjectDoesNotExist, ImproperlyConfigured
from django.core.urlresolvers import resolve, get_script_prefix, NoReverseMatch, Resolver404
from django.db.models.query import QuerySet
from django.utils import six
from django.utils.translation import ugettext_lazy as _


class PKOnlyObject(object):
    def __init__(self, pk):
        self.pk = pk


class RelatedField(Field):
    def __init__(self, **kwargs):
        self.queryset = kwargs.pop('queryset', None)
        assert self.queryset is not None or kwargs.get('read_only', None), (
            'Relational field must provide a `queryset` argument, '
            'or set read_only=`True`.'
        )
        assert not (self.queryset is not None and kwargs.get('read_only', None)), (
            'Relational fields should not provide a `queryset` argument, '
            'when setting read_only=`True`.'
        )
        super(RelatedField, self).__init__(**kwargs)

    def __new__(cls, *args, **kwargs):
        # We override this method in order to automagically create
        # `ManyRelation` classes instead when `many=True` is set.
        if kwargs.pop('many', False):
            return ManyRelation(
                child_relation=cls(*args, **kwargs),
                read_only=kwargs.get('read_only', False)
            )
        return super(RelatedField, cls).__new__(cls, *args, **kwargs)

    def run_validation(self, data=empty):
        # We force empty strings to None values for relational fields.
        if data == '':
            data = None
        return super(RelatedField, self).run_validation(data)

    def get_queryset(self):
        queryset = self.queryset
        if isinstance(queryset, QuerySet):
            # Ensure queryset is re-evaluated whenever used.
            queryset = queryset.all()
        return queryset

    def get_iterable(self, instance, source):
        relationship = get_attribute(instance, [source])
        return relationship.all() if (hasattr(relationship, 'all')) else relationship

    @property
    def choices(self):
        return dict([
            (
                str(self.to_representation(item)),
                str(item)
            )
            for item in self.queryset.all()
        ])


class StringRelatedField(RelatedField):
    """
    A read only field that represents its targets using their
    plain string representation.
    """

    def __init__(self, **kwargs):
        kwargs['read_only'] = True
        super(StringRelatedField, self).__init__(**kwargs)

    def to_representation(self, value):
        return six.text_type(value)


class PrimaryKeyRelatedField(RelatedField):
    default_error_messages = {
        'required': 'This field is required.',
        'does_not_exist': "Invalid pk '{pk_value}' - object does not exist.",
        'incorrect_type': 'Incorrect type. Expected pk value, received {data_type}.',
    }

    def to_internal_value(self, data):
        try:
            return self.get_queryset().get(pk=data)
        except ObjectDoesNotExist:
            self.fail('does_not_exist', pk_value=data)
        except (TypeError, ValueError):
            self.fail('incorrect_type', data_type=type(data).__name__)

    def get_attribute(self, instance):
        # We customize `get_attribute` here for performance reasons.
        # For relationships the instance will already have the pk of
        # the related object. We return this directly instead of returning the
        # object itself, which would require a database lookup.
        try:
            return PKOnlyObject(pk=instance.serializable_value(self.source))
        except AttributeError:
            return get_attribute(instance, [self.source])

    def get_iterable(self, instance, source):
        # For consistency with `get_attribute` we're using `serializable_value()`
        # here. Typically there won't be any difference, but some custom field
        # types might return a non-primative value for the pk otherwise.
        #
        # We could try to get smart with `values_list('pk', flat=True)`, which
        # would be better in some case, but would actually end up with *more*
        # queries if the developer is using `prefetch_related` across the
        # relationship.
        relationship = super(PrimaryKeyRelatedField, self).get_iterable(instance, source)
        return [
            PKOnlyObject(pk=item.serializable_value('pk'))
            for item in relationship
        ]

    def to_representation(self, value):
        return value.pk


class HyperlinkedRelatedField(RelatedField):
    lookup_field = 'pk'

    default_error_messages = {
        'required': 'This field is required.',
        'no_match': 'Invalid hyperlink - No URL match',
        'incorrect_match': 'Invalid hyperlink - Incorrect URL match.',
        'does_not_exist': 'Invalid hyperlink - Object does not exist.',
        'incorrect_type': 'Incorrect type. Expected URL string, received {data_type}.',
    }

    def __init__(self, view_name=None, **kwargs):
        assert view_name is not None, 'The `view_name` argument is required.'
        self.view_name = view_name
        self.lookup_field = kwargs.pop('lookup_field', self.lookup_field)
        self.lookup_url_kwarg = kwargs.pop('lookup_url_kwarg', self.lookup_field)
        self.format = kwargs.pop('format', None)

        # We include these simply for dependency injection in tests.
        # We can't add them as class attributes or they would expect an
        # implicit `self` argument to be passed.
        self.reverse = reverse
        self.resolve = resolve

        super(HyperlinkedRelatedField, self).__init__(**kwargs)

    def get_object(self, view_name, view_args, view_kwargs):
        """
        Return the object corresponding to a matched URL.

        Takes the matched URL conf arguments, and should return an
        object instance, or raise an `ObjectDoesNotExist` exception.
        """
        lookup_value = view_kwargs[self.lookup_url_kwarg]
        lookup_kwargs = {self.lookup_field: lookup_value}
        return self.get_queryset().get(**lookup_kwargs)

    def get_url(self, obj, view_name, request, format):
        """
        Given an object, return the URL that hyperlinks to the object.

        May raise a `NoReverseMatch` if the `view_name` and `lookup_field`
        attributes are not configured to correctly match the URL conf.
        """
        # Unsaved objects will not yet have a valid URL.
        if obj.pk is None:
            return None

        lookup_value = getattr(obj, self.lookup_field)
        kwargs = {self.lookup_url_kwarg: lookup_value}
        return self.reverse(view_name, kwargs=kwargs, request=request, format=format)

    def to_internal_value(self, data):
        try:
            http_prefix = data.startswith(('http:', 'https:'))
        except AttributeError:
            self.fail('incorrect_type', data_type=type(data).__name__)

        if http_prefix:
            # If needed convert absolute URLs to relative path
            data = urlparse.urlparse(data).path
            prefix = get_script_prefix()
            if data.startswith(prefix):
                data = '/' + data[len(prefix):]

        try:
            match = self.resolve(data)
        except Resolver404:
            self.fail('no_match')

        if match.view_name != self.view_name:
            self.fail('incorrect_match')

        try:
            return self.get_object(match.view_name, match.args, match.kwargs)
        except (ObjectDoesNotExist, TypeError, ValueError):
            self.fail('does_not_exist')

    def to_representation(self, value):
        request = self.context.get('request', None)
        format = self.context.get('format', None)

        assert request is not None, (
            "`%s` requires the request in the serializer"
            " context. Add `context={'request': request}` when instantiating "
            "the serializer." % self.__class__.__name__
        )

        # By default use whatever format is given for the current context
        # unless the target is a different type to the source.
        #
        # Eg. Consider a HyperlinkedIdentityField pointing from a json
        # representation to an html property of that representation...
        #
        # '/snippets/1/' should link to '/snippets/1/highlight/'
        # ...but...
        # '/snippets/1/.json' should link to '/snippets/1/highlight/.html'
        if format and self.format and self.format != format:
            format = self.format

        # Return the hyperlink, or error if incorrectly configured.
        try:
            return self.get_url(value, self.view_name, request, format)
        except NoReverseMatch:
            msg = (
                'Could not resolve URL for hyperlinked relationship using '
                'view name "%s". You may have failed to include the related '
                'model in your API, or incorrectly configured the '
                '`lookup_field` attribute on this field.'
            )
            raise ImproperlyConfigured(msg % self.view_name)


class HyperlinkedIdentityField(HyperlinkedRelatedField):
    """
    A read-only field that represents the identity URL for an object, itself.

    This is in contrast to `HyperlinkedRelatedField` which represents the
    URL of relationships to other objects.
    """

    def __init__(self, view_name=None, **kwargs):
        assert view_name is not None, 'The `view_name` argument is required.'
        kwargs['read_only'] = True
        kwargs['source'] = '*'
        super(HyperlinkedIdentityField, self).__init__(view_name, **kwargs)


class SlugRelatedField(RelatedField):
    """
    A read-write field the represents the target of the relationship
    by a unique 'slug' attribute.
    """

    default_error_messages = {
        'does_not_exist': _("Object with {slug_name}={value} does not exist."),
        'invalid': _('Invalid value.'),
    }

    def __init__(self, slug_field=None, **kwargs):
        assert slug_field is not None, 'The `slug_field` argument is required.'
        self.slug_field = slug_field
        super(SlugRelatedField, self).__init__(**kwargs)

    def to_internal_value(self, data):
        try:
            return self.get_queryset().get(**{self.slug_field: data})
        except ObjectDoesNotExist:
            self.fail('does_not_exist', slug_name=self.slug_field, value=smart_text(data))
        except (TypeError, ValueError):
            self.fail('invalid')

    def to_representation(self, obj):
        return getattr(obj, self.slug_field)


class ManyRelation(Field):
    """
    Relationships with `many=True` transparently get coerced into instead being
    a ManyRelation with a child relationship.

    The `ManyRelation` class is responsible for handling iterating through
    the values and passing each one to the child relationship.

    You shouldn't need to be using this class directly yourself.
    """
    initial = []
    default_empty_html = []

    def __init__(self, child_relation=None, *args, **kwargs):
        self.child_relation = child_relation
        assert child_relation is not None, '`child_relation` is a required argument.'
        super(ManyRelation, self).__init__(*args, **kwargs)
        self.child_relation.bind(field_name='', parent=self)

    def get_value(self, dictionary):
        # We override the default field access in order to support
        # lists in HTML forms.
        if html.is_html_input(dictionary):
            return dictionary.getlist(self.field_name)
        return dictionary.get(self.field_name, empty)

    def to_internal_value(self, data):
        return [
            self.child_relation.to_internal_value(item)
            for item in data
        ]

    def get_attribute(self, instance):
        return self.child_relation.get_iterable(instance, self.source)

    def to_representation(self, iterable):
        return [
            self.child_relation.to_representation(value)
            for value in iterable
        ]

    @property
    def choices(self):
        queryset = self.child_relation.queryset
        iterable = queryset.all() if (hasattr(queryset, 'all')) else queryset
        items_and_representations = [
            (item, self.child_relation.to_representation(item))
            for item in iterable
        ]
        return dict([
            (
                str(item_representation),
                str(item) + ' - ' + str(item_representation)
            )
            for item, item_representation in items_and_representations
        ])