"""Add ondelete to transitive FK constraints.

Without these, deleting a user would fail because the DB-level CASCADE
only reaches first-level children (calendars, projects, people, locations).
Second-level children (calendar_events via calendar_id, project_tasks via
project_id, etc.) need their own ondelete rules to allow the full cascade.

FK changes:
  calendar_events.calendar_id  → CASCADE   (events die with calendar)
  calendar_events.location_id  → SET NULL  (optional ref, just unlink)
  project_tasks.project_id     → CASCADE   (tasks die with project)
  project_tasks.person_id      → SET NULL  (optional assignee, just unlink)
  todos.project_id             → SET NULL  (optional ref, just unlink)

Revision ID: 036
Revises: 035
Create Date: 2026-02-27
"""
from alembic import op

revision = "036"
down_revision = "035"
branch_labels = None
depends_on = None


def upgrade() -> None:
    # calendar_events.calendar_id → CASCADE
    op.drop_constraint(
        "fk_calendar_events_calendar_id", "calendar_events", type_="foreignkey"
    )
    op.create_foreign_key(
        "fk_calendar_events_calendar_id",
        "calendar_events",
        "calendars",
        ["calendar_id"],
        ["id"],
        ondelete="CASCADE",
    )

    # calendar_events.location_id → SET NULL
    op.drop_constraint(
        "calendar_events_location_id_fkey", "calendar_events", type_="foreignkey"
    )
    op.create_foreign_key(
        "calendar_events_location_id_fkey",
        "calendar_events",
        "locations",
        ["location_id"],
        ["id"],
        ondelete="SET NULL",
    )

    # project_tasks.project_id → CASCADE
    op.drop_constraint(
        "project_tasks_project_id_fkey", "project_tasks", type_="foreignkey"
    )
    op.create_foreign_key(
        "project_tasks_project_id_fkey",
        "project_tasks",
        "projects",
        ["project_id"],
        ["id"],
        ondelete="CASCADE",
    )

    # project_tasks.person_id → SET NULL
    op.drop_constraint(
        "project_tasks_person_id_fkey", "project_tasks", type_="foreignkey"
    )
    op.create_foreign_key(
        "project_tasks_person_id_fkey",
        "project_tasks",
        "people",
        ["person_id"],
        ["id"],
        ondelete="SET NULL",
    )

    # todos.project_id → SET NULL
    op.drop_constraint(
        "todos_project_id_fkey", "todos", type_="foreignkey"
    )
    op.create_foreign_key(
        "todos_project_id_fkey",
        "todos",
        "projects",
        ["project_id"],
        ["id"],
        ondelete="SET NULL",
    )


def downgrade() -> None:
    # Reverse: remove ondelete by re-creating without it
    for table, col, ref_table, constraint in [
        ("todos", "project_id", "projects", "todos_project_id_fkey"),
        ("project_tasks", "person_id", "people", "project_tasks_person_id_fkey"),
        ("project_tasks", "project_id", "projects", "project_tasks_project_id_fkey"),
        ("calendar_events", "location_id", "locations", "calendar_events_location_id_fkey"),
        ("calendar_events", "calendar_id", "calendars", "fk_calendar_events_calendar_id"),
    ]:
        op.drop_constraint(constraint, table, type_="foreignkey")
        op.create_foreign_key(constraint, table, ref_table, [col], ["id"])