"""GEMS Pass 2: add repo_id FK to workstreams (ADR-001 alignment)

Revision ID: f2a3b4c5d6e7
Revises: e1f2a3b4c5d6
Create Date: 2026-03-02 00:00:00.000000
"""
from typing import Sequence, Union

import sqlalchemy as sa
from alembic import op
from sqlalchemy.dialects import postgresql

revision: str = "f2a3b4c5d6e7"
down_revision: Union[str, None] = "e1f2a3b4c5d6"
branch_labels: Union[str, Sequence[str], None] = None
depends_on: Union[str, Sequence[str], None] = None


def upgrade() -> None:
    op.add_column(
        "workstreams",
        sa.Column("repo_id", postgresql.UUID(as_uuid=True), nullable=True),
    )
    op.create_foreign_key(
        "fk_workstream_repo_id",
        "workstreams", "managed_repos",
        ["repo_id"], ["id"],
        ondelete="SET NULL",
    )
    op.create_index("ix_workstreams_repo_id", "workstreams", ["repo_id"])

    # Best-effort backfill: topic → domain → first repo (by created_at)
    # Records with no repo in their domain remain NULL (requires manual resolution)
    op.execute("""
        UPDATE workstreams ws
        SET repo_id = sub.repo_id
        FROM (
            SELECT DISTINCT ON (ws.id)
                ws.id   AS ws_id,
                mr.id   AS repo_id
            FROM workstreams ws
            JOIN topics      t  ON t.id  = ws.topic_id
            JOIN managed_repos mr ON mr.domain_id = t.domain_id
            WHERE mr.status = 'active'
            ORDER BY ws.id, mr.created_at
        ) sub
        WHERE ws.id = sub.ws_id
    """)


def downgrade() -> None:
    op.drop_index("ix_workstreams_repo_id", table_name="workstreams")
    op.drop_constraint("fk_workstream_repo_id", "workstreams", type_="foreignkey")
    op.drop_column("workstreams", "repo_id")