from django.db import models

from funkwhale_api.common import fields
from funkwhale_api.favorites.models import TrackFavorite
from funkwhale_api.history.models import Listening


def combined_recent(limit, **kwargs):
    datetime_field = kwargs.pop('datetime_field', 'creation_date')
    source_querysets = {
        qs.model._meta.label: qs for qs in kwargs.pop('querysets')
    }
    querysets = {
        k: qs.annotate(
            __type=models.Value(
                qs.model._meta.label, output_field=models.CharField()
            )
        ).values('pk', datetime_field, '__type')
        for k, qs in source_querysets.items()
    }
    _qs_list = list(querysets.values())
    union_qs = _qs_list[0].union(*_qs_list[1:])
    records = []
    for row in union_qs.order_by('-{}'.format(datetime_field))[:limit]:
        records.append({
            'type': row['__type'],
            'when': row[datetime_field],
            'pk': row['pk']
        })
    # Now we bulk-load each object type in turn
    to_load = {}
    for record in records:
        to_load.setdefault(record['type'], []).append(record['pk'])
    fetched = {}

    for key, pks in to_load.items():
        for item in source_querysets[key].filter(pk__in=pks):
            fetched[(key, item.pk)] = item

    # Annotate 'records' with loaded objects
    for record in records:
        record['object'] = fetched[(record['type'], record['pk'])]
    return records


def get_activity(user, limit=20):
    query = fields.privacy_level_query(
        user, lookup_field='user__privacy_level')
    querysets = [
        Listening.objects.filter(query).select_related(
            'track',
            'user',
            'track__artist',
            'track__album__artist',
        ),
        TrackFavorite.objects.filter(query).select_related(
            'track',
            'user',
            'track__artist',
            'track__album__artist',
        ),
    ]
    records = combined_recent(limit=limit, querysets=querysets)
    return [r['object'] for r in records]