''' basics for an activitypub serializer '''
from dataclasses import dataclass, fields, MISSING
from json import JSONEncoder

from django.apps import apps
from django.db import IntegrityError, transaction

from bookwyrm.connectors import ConnectorException, get_data
from bookwyrm.tasks import app

class ActivitySerializerError(ValueError):
    ''' routine problems serializing activitypub json '''


class ActivityEncoder(JSONEncoder):
    '''  used to convert an Activity object into json '''
    def default(self, o):
        return o.__dict__


@dataclass
class Link:
    ''' for tagging a book in a status '''
    href: str
    name: str
    type: str = 'Link'


@dataclass
class Mention(Link):
    ''' a subtype of Link for mentioning an actor '''
    type: str = 'Mention'


@dataclass
class Signature:
    ''' public key block '''
    creator: str
    created: str
    signatureValue: str
    type: str = 'RsaSignature2017'

def naive_parse(activity_objects, activity_json, serializer=None):
    ''' this navigates circular import issues '''
    if not serializer:
        if activity_json.get('publicKeyPem'):
            # ugh
            activity_json['type'] = 'PublicKey'
        try:
            activity_type = activity_json['type']
            serializer = activity_objects[activity_type]
        except KeyError as e:
            raise ActivitySerializerError(e)

    return serializer(activity_objects=activity_objects, **activity_json)


@dataclass(init=False)
class ActivityObject:
    ''' actor activitypub json '''
    id: str
    type: str

    def __init__(self, activity_objects=None, **kwargs):
        ''' this lets you pass in an object with fields that aren't in the
        dataclass, which it ignores. Any field in the dataclass is required or
        has a default value '''
        for field in fields(self):
            try:
                value = kwargs[field.name]
                if value in (None, MISSING):
                    raise KeyError()
                try:
                    is_subclass = issubclass(field.type, ActivityObject)
                except TypeError:
                    is_subclass = False
                # serialize a model obj
                if hasattr(value, 'to_activity'):
                    value = value.to_activity()
                # parse a dict into the appropriate activity
                elif is_subclass and isinstance(value, dict):
                    if activity_objects:
                        value = naive_parse(activity_objects, value)
                    else:
                        value = naive_parse(activity_objects, value, serializer=field.type)

            except KeyError:
                if field.default == MISSING and \
                        field.default_factory == MISSING:
                    raise ActivitySerializerError(\
                            'Missing required field: %s' % field.name)
                value = field.default
            setattr(self, field.name, value)


    def to_model(self, model=None, instance=None, allow_create=True, save=True):
        ''' convert from an activity to a model instance '''
        model = model or get_model_from_type(self.type)

        # only reject statuses if we're potentially creating them
        if allow_create and \
                hasattr(model, 'ignore_activity') and \
                model.ignore_activity(self):
            return None

        # check for an existing instance
        instance = instance or model.find_existing(self.serialize())

        if not instance and not allow_create:
            # so that we don't create when we want to delete or update
            return None
        instance = instance or model()

        for field in instance.simple_fields:
            try:
                field.set_field_from_activity(instance, self)
            except AttributeError as e:
                raise ActivitySerializerError(e)

        # image fields have to be set after other fields because they can save
        # too early and jank up users
        for field in instance.image_fields:
            field.set_field_from_activity(instance, self, save=save)

        if not save:
            return instance

        with transaction.atomic():
            # we can't set many to many and reverse fields on an unsaved object
            try:
                try:
                    instance.save(broadcast=False)
                except TypeError:
                    instance.save()
            except IntegrityError as e:
                raise ActivitySerializerError(e)

            # add many to many fields, which have to be set post-save
            for field in instance.many_to_many_fields:
                # mention books/users, for example
                field.set_field_from_activity(instance, self)

        # reversed relationships in the models
        for (model_field_name, activity_field_name) in \
                instance.deserialize_reverse_fields:
            # attachments on Status, for example
            values = getattr(self, activity_field_name)
            if values is None or values is MISSING:
                continue

            model_field = getattr(model, model_field_name)
            # creating a Work, model_field is 'editions'
            # creating a User, model field is 'key_pair'
            related_model = model_field.field.model
            related_field_name = model_field.field.name

            for item in values:
                set_related_field.delay(
                    related_model.__name__,
                    instance.__class__.__name__,
                    related_field_name,
                    instance.remote_id,
                    item
                )
        return instance


    def serialize(self):
        ''' convert to dictionary with context attr '''
        data = self.__dict__.copy()
        # recursively serialize
        for (k, v) in data.items():
            try:
                if issubclass(type(v), ActivityObject):
                    data[k] = v.serialize()
            except TypeError:
                pass
        data = {k:v for (k, v) in data.items() if v is not None}
        data['@context'] = 'https://www.w3.org/ns/activitystreams'
        return data


@app.task
@transaction.atomic
def set_related_field(
        model_name, origin_model_name, related_field_name,
        related_remote_id, data):
    ''' load reverse related fields (editions, attachments) without blocking '''
    model = apps.get_model('bookwyrm.%s' % model_name, require_ready=True)
    origin_model = apps.get_model(
        'bookwyrm.%s' % origin_model_name,
        require_ready=True
    )

    with transaction.atomic():
        if isinstance(data, str):
            existing = model.find_existing_by_remote_id(data)
            if existing:
                data = existing.to_activity()
            else:
                data = get_data(data)
        activity = model.activity_serializer(**data)

        # this must exist because it's the object that triggered this function
        instance = origin_model.find_existing_by_remote_id(related_remote_id)
        if not instance:
            raise ValueError(
                'Invalid related remote id: %s' % related_remote_id)

        # set the origin's remote id on the activity so it will be there when
        # the model instance is created
        # edition.parentWork = instance, for example
        model_field = getattr(model, related_field_name)
        if hasattr(model_field, 'activitypub_field'):
            setattr(
                activity,
                getattr(model_field, 'activitypub_field'),
                instance.remote_id
            )
        item = activity.to_model()

        # if the related field isn't serialized (attachments on Status), then
        # we have to set it post-creation
        if not hasattr(model_field, 'activitypub_field'):
            setattr(item, related_field_name, instance)
            item.save()


def get_model_from_type(activity_type):
    ''' given the activity, what type of model '''
    models = apps.get_models()
    model = [m for m in models if hasattr(m, 'activity_serializer') and \
        hasattr(m.activity_serializer, 'type') and \
        m.activity_serializer.type == activity_type]
    if not model:
        raise ActivitySerializerError(
            'No model found for activity type "%s"' % activity_type)
    return model[0]


def resolve_remote_id(remote_id, model=None, refresh=False, save=True):
    ''' take a remote_id and return an instance, creating if necessary '''
    if model:# a bonus check we can do if we already know the model
        result = model.find_existing_by_remote_id(remote_id)
        if result and not refresh:
            return result

    # load the data and create the object
    try:
        data = get_data(remote_id)
    except (ConnectorException, ConnectionError):
        raise ActivitySerializerError(
            'Could not connect to host for remote_id in %s model: %s' % \
                (model.__name__, remote_id))
    # determine the model implicitly, if not provided
    if not model:
        model = get_model_from_type(data.get('type'))

    # check for existing items with shared unique identifiers
    result = model.find_existing(data)
    if result and not refresh:
        return result

    item = model.activity_serializer(**data)
    # if we're refreshing, "result" will be set and we'll update it
    return item.to_model(model=model, instance=result, save=save)