''' handles all of the activity coming in to the server '''
import json
from base64 import b64decode
from urllib.parse import urldefrag

from Crypto.Hash import SHA256
from Crypto.PublicKey import RSA
from Crypto.Signature import pkcs1_15
import django.db.utils
from django.http import HttpResponse
from django.http import HttpResponseBadRequest, HttpResponseNotFound
from django.views.decorators.csrf import csrf_exempt
import requests

from fedireads import books_manager, models, outgoing
from fedireads import status as status_builder
from fedireads.remote_user import get_or_create_remote_user
from fedireads.tasks import app


@csrf_exempt
def inbox(request, username):
    ''' incoming activitypub events '''
    # TODO: should do some kind of checking if the user accepts
    # this action from the sender probably? idk
    # but this will just throw a 404 if the user doesn't exist
    try:
        models.User.objects.get(localname=username)
    except models.User.DoesNotExist:
        return HttpResponseNotFound()

    return shared_inbox(request)


@csrf_exempt
def shared_inbox(request):
    ''' incoming activitypub events '''
    # TODO: should this be functionally different from the non-shared inbox??
    if request.method == 'GET':
        return HttpResponseNotFound()

    try:
        activity = json.loads(request.body)
    except json.decoder.JSONDecodeError:
        return HttpResponseBadRequest()

    if not activity.get('object'):
        return HttpResponseBadRequest()

    try:
        verify_signature(activity.get('actor'), request)
    except ValueError:
        return HttpResponse(status=401)

    handlers = {
        'Follow': handle_follow,
        'Accept': handle_follow_accept,
        'Reject': handle_follow_reject,
        'Create': handle_create,
        'Like': handle_favorite,
        'Announce': handle_boost,
        'Add': {
            'Tag': handle_tag,
        },
        'Undo': {
            'Follow': handle_unfollow,
            'Like': handle_unfavorite,
        },
        'Update': {
            'Person': None,# TODO: handle_update_user
            'Document': handle_update_book,
        },
    }
    activity_type = activity['type']

    handler = handlers.get(activity_type, None)
    if isinstance(handler, dict):
        handler = handler.get(activity['object']['type'], None)

    if not handler:
        return HttpResponseNotFound()

    handler.delay(activity)
    return HttpResponse()


def get_public_key(key_actor):
    try:
        user = models.User.objects.get(actor=key_actor)
        public_key = user.public_key
        actor = user.actor
    except models.User.DoesNotExist:
        response = requests.get(
            key_actor,
            headers={'Accept': 'application/activity+json'}
        )
        if not response.ok:
            raise ValueError('Could not load public key')
        user_data = response.json()
        public_key = user_data['publicKey']['publicKeyPem']

    return RSA.import_key(public_key)

def verify_signature(required_actor, request):
    ''' verify rsa signature '''
    signature_dict = {}
    for pair in request.headers['Signature'].split(','):
        k, v = pair.split('=', 1)
        v = v.replace('"', '')
        signature_dict[k] = v

    try:
        key_id = signature_dict['keyId']
        headers = signature_dict['headers']
        signature = b64decode(signature_dict['signature'])
    except KeyError:
        raise ValueError('Invalid auth header')

    # TODO Use the fragment - actors can have multiple keys?
    key_actor = urldefrag(key_id).url

    if key_actor != required_actor:
        raise ValueError("Wrong actor created signature.")

    key = get_public_key(key_actor)

    comparison_string = []
    for signed_header_name in headers.split(' '):
        if signed_header_name == '(request-target)':
            comparison_string.append('(request-target): post %s' % request.path)
        else:
            comparison_string.append('%s: %s' % (
                signed_header_name,
                request.headers[signed_header_name]
            ))
    comparison_string = '\n'.join(comparison_string)

    signer = pkcs1_15.new(key)
    digest = SHA256.new()
    digest.update(comparison_string.encode())

    # raises a ValueError if it fails
    signer.verify(digest, signature)


@app.task
def handle_follow(activity):
    ''' someone wants to follow a local user '''
    # figure out who they want to follow -- not using get_or_create because
    # we only allow you to follow local users
    try:
        to_follow = models.User.objects.get(actor=activity['object'])
    except models.User.DoesNotExist:
        return False
    # figure out who the actor is
    user = get_or_create_remote_user(activity['actor'])
    try:
        request = models.UserFollowRequest.objects.create(
            user_subject=user,
            user_object=to_follow,
            relationship_id=activity['id']
        )
    except django.db.utils.IntegrityError as err:
        if err.__cause__.diag.constraint_name != 'userfollowrequest_unique':
            raise
        # Duplicate follow request. Not sure what the correct behaviour is, but
        # just dropping it works for now. We should perhaps generate the
        # Accept, but then do we need to match the activity id?
        return

    if not to_follow.manually_approves_followers:
        status_builder.create_notification(
            to_follow,
            'FOLLOW',
            related_user=user
        )
        outgoing.handle_accept(user, to_follow, request)
    else:
        status_builder.create_notification(
            to_follow,
            'FOLLOW_REQUEST',
            related_user=user
        )


@app.task
def handle_unfollow(activity):
    ''' unfollow a local user '''
    obj = activity['object']
    try:
        requester = get_or_create_remote_user(obj['actor'])
        to_unfollow = models.User.objects.get(actor=obj['object'])
    except models.User.DoesNotExist:
        return False

    to_unfollow.followers.remove(requester)


@app.task
def handle_follow_accept(activity):
    ''' hurray, someone remote accepted a follow request '''
    # figure out who they want to follow
    requester = models.User.objects.get(actor=activity['object']['actor'])
    # figure out who they are
    accepter = get_or_create_remote_user(activity['actor'])

    try:
        request = models.UserFollowRequest.objects.get(
            user_subject=requester,
            user_object=accepter
        )
        request.delete()
    except models.UserFollowRequest.DoesNotExist:
        pass
    accepter.followers.add(requester)


@app.task
def handle_follow_reject(activity):
    ''' someone is rejecting a follow request '''
    requester = models.User.objects.get(actor=activity['object']['actor'])
    rejecter = get_or_create_remote_user(activity['actor'])

    try:
        request = models.UserFollowRequest.objects.get(
            user_subject=requester,
            user_object=rejecter
        )
        request.delete()
    except models.UserFollowRequest.DoesNotExist:
        return False


@app.task
def handle_create(activity):
    ''' someone did something, good on them '''
    user = get_or_create_remote_user(activity['actor'])

    if user.local:
        # we really oughtn't even be sending in this case
        return True

    if activity['object'].get('fedireadsType') and \
            'inReplyToBook' in activity['object']:
        if activity['object']['fedireadsType'] == 'Review':
            builder = status_builder.create_review_from_activity
        elif activity['object']['fedireadsType'] == 'Quotation':
            builder = status_builder.create_quotation_from_activity
        else:
            builder = status_builder.create_comment_from_activity

        # create the status, it'll throw a ValueError if anything is missing
        builder(user, activity['object'])
    elif activity['object'].get('inReplyTo'):
        # only create the status if it's in reply to a status we already know
        if not status_builder.get_status(activity['object']['inReplyTo']):
            return True

        status = status_builder.create_status_from_activity(
            user,
            activity['object']
        )
        if status and status.reply_parent:
            status_builder.create_notification(
                status.reply_parent.user,
                'REPLY',
                related_user=status.user,
                related_status=status,
            )
    return True


@app.task
def handle_favorite(activity):
    ''' approval of your good good post '''
    try:
        status_id = activity['object'].split('/')[-1]
        status = models.Status.objects.get(id=status_id)
        liker = get_or_create_remote_user(activity['actor'])
    except (models.Status.DoesNotExist, models.User.DoesNotExist):
        return False

    if not liker.local:
        status_builder.create_favorite_from_activity(liker, activity)

    status_builder.create_notification(
        status.user,
        'FAVORITE',
        related_user=liker,
        related_status=status,
    )


@app.task
def handle_unfavorite(activity):
    ''' approval of your good good post '''
    favorite_id = activity['object']['id']
    fav = status_builder.get_favorite(favorite_id)
    if not fav:
        return False

    fav.delete()


@app.task
def handle_boost(activity):
    ''' someone gave us a boost! '''
    try:
        status_id = activity['object'].split('/')[-1]
        status = models.Status.objects.get(id=status_id)
        booster = get_or_create_remote_user(activity['actor'])
    except (models.Status.DoesNotExist, models.User.DoesNotExist):
        return False

    if not booster.local:
        status_builder.create_boost_from_activity(booster, activity)

    status_builder.create_notification(
        status.user,
        'BOOST',
        related_user=booster,
        related_status=status,
    )


@app.task
def handle_tag(activity):
    ''' someone is tagging a book '''
    user = get_or_create_remote_user(activity['actor'])
    if not user.local:
        book = activity['target']['id']
        status_builder.create_tag(user, book, activity['object']['name'])


@app.task
def handle_update_book(activity):
    ''' a remote instance changed a book (Document) '''
    document = activity['object']
    # check if we have their copy and care about their updates
    book = models.Book.objects.select_subclasses().filter(
        remote_id=document['url'],
        sync=True,
    ).first()
    if not book:
        return

    books_manager.update_book(book, data=document)