"""add last_read_at to conversation_participants (DM unread tracking)

Revision ID: 0011_add_dm_last_read
Revises: 0010_add_profile_tables
Create Date: 2026-09-15 00:00:00.000000

app/routers/chat_dm.py (DM send/list/conversations endpoints). Unread-count
tracking is implemented as a last-read timestamp per participant: whenever a
user fetches a conversation's message history, their
``conversation_participants`` row's ``last_read_at`` is bumped to "now", and
the conversation-list endpoint counts messages with
``created_at > last_read_at`` (or all messages if never read) as unread for
that participant. Nullable/no default so existing rows (none yet in
practice, but consistent with "never read") read as "everything unread".
"""
from typing import Sequence, Union

from alembic import op
import sqlalchemy as sa

# revision identifiers, used by Alembic.
revision: str = "0011_add_dm_last_read"
down_revision: Union[str, None] = "0010_add_profile_tables"
branch_labels: Union[str, Sequence[str], None] = None
depends_on: Union[str, Sequence[str], None] = None


def upgrade() -> None:
    op.add_column(
        "conversation_participants",
        sa.Column("last_read_at", sa.DateTime(timezone=True), nullable=True),
    )


def downgrade() -> None:
    op.drop_column("conversation_participants", "last_read_at")