from __future__ import annotations

from django.db import transaction
from django.db.models import F, Q
from django.utils import timezone

from communications.mentions import mentioned_user_ids
from communications.models import ChatReadState, Message
from notifications.push_lifecycle import delete_message_notifications


def soft_delete_message(
    message: Message,
    *,
    deleted_by,
    replacement_content: str | None = None,
) -> bool:
    """Soft-delete a message and remove it from cached unread counters."""
    with transaction.atomic():
        locked_message = Message.objects.select_for_update().get(pk=message.pk)
        if locked_message.is_deleted:
            return False

        unread_states = ChatReadState.objects.filter(
            chat_id=locked_message.chat_id,
            unread_count__gt=0,
        ).exclude(user_id=locked_message.author_id)
        unread_states = unread_states.filter(
            Q(last_read_message_id__isnull=True)
            | Q(last_read_message_id__lt=locked_message.id)
        )
        unread_states.update(unread_count=F("unread_count") - 1)

        mention_recipient_ids = mentioned_user_ids(locked_message.mentions)
        if mention_recipient_ids:
            unread_states.filter(
                user_id__in=mention_recipient_ids,
                unread_mention_count__gt=0,
            ).update(unread_mention_count=F("unread_mention_count") - 1)

        locked_message.is_deleted = True
        locked_message.deleted_at = timezone.now()
        locked_message.deleted_by = deleted_by
        update_fields = ["is_deleted", "deleted_at", "deleted_by"]
        if replacement_content is not None:
            locked_message.content = replacement_content
            update_fields.append("content")
        locked_message.save(update_fields=update_fields)

        delete_message_notifications(
            chat_id=locked_message.chat_id,
            message_id=locked_message.id,
        )

        message.is_deleted = locked_message.is_deleted
        message.deleted_at = locked_message.deleted_at
        message.deleted_by = locked_message.deleted_by
        if replacement_content is not None:
            message.content = replacement_content
        return True