"""add parent_message_id to messages

Revision ID: d57ba9ebb251
Revises: 675b5321501b
Create Date: 2024-09-11 10:12:45.826265

"""
import sqlalchemy as sa
from alembic import op

import models as models


def _is_pg(conn):
    return conn.dialect.name == "postgresql"

# revision identifiers, used by Alembic.
revision = 'd57ba9ebb251'
down_revision = '675b5321501b'
branch_labels = None
depends_on = None


def upgrade():
    # ### commands auto generated by Alembic - please adjust! ###
    with op.batch_alter_table('messages', schema=None) as batch_op:
        batch_op.add_column(sa.Column('parent_message_id', models.types.StringUUID(), nullable=True))

    # Set parent_message_id for existing messages to distinguish them from new messages with actual parent IDs or NULLs
    conn = op.get_bind()
    if _is_pg(conn):
        # PostgreSQL: Use uuid_nil() function
        op.execute('UPDATE messages SET parent_message_id = uuid_nil() WHERE parent_message_id IS NULL')
    else:
        # MySQL: Use a specific UUID value to represent nil
        op.execute("UPDATE messages SET parent_message_id = '00000000-0000-0000-0000-000000000000' WHERE parent_message_id IS NULL")

    # ### end Alembic commands ###


def downgrade():
    # ### commands auto generated by Alembic - please adjust! ###
    with op.batch_alter_table('messages', schema=None) as batch_op:
        batch_op.drop_column('parent_message_id')

    # ### end Alembic commands ###