"""add_unique_constraint_friendship

Revision ID: a2b3c4d5e6f7
Revises: f4e8a1b2c3d9
Create Date: 2026-03-29 00:00:00.000000

"""
from typing import Sequence, Union

from alembic import op
from sqlalchemy import text


# revision identifiers, used by Alembic.
revision: str = 'a2b3c4d5e6f7'
down_revision: Union[str, Sequence[str], None] = 'f4e8a1b2c3d9'
branch_labels: Union[str, Sequence[str], None] = None
depends_on: Union[str, Sequence[str], None] = None


def upgrade() -> None:
    # Remove duplicate (requester_id, addressee_id) pairs that already exist,
    # keeping the earliest row per pair before adding the unique constraint.
    conn = op.get_bind()
    conn.execute(text("""
        DELETE FROM friendships
        WHERE id IN (
            SELECT id FROM (
                SELECT id,
                       ROW_NUMBER() OVER (
                           PARTITION BY requester_id, addressee_id
                           ORDER BY created_at
                       ) AS rn
                FROM friendships
            ) sub
            WHERE rn > 1
        )
    """))

    op.create_unique_constraint(
        "uq_friendship_requester_addressee",
        "friendships",
        ["requester_id", "addressee_id"],
    )


def downgrade() -> None:
    op.drop_constraint("uq_friendship_requester_addressee", "friendships", type_="unique")