-- 039_requisition_department_id.sql
-- Many requisitions -> one department. Adds requisitions.department_id, the FK
-- behind Requisition.department_id / Requisition.department and
-- Department.requisitions (backend/candidate_forms/models.py,
-- backend/department/models.py).
--
-- A new file, not an edit to 020 or 038: manual migrations run once and are
-- recorded in manual_migrations, so changes to an applied file never reach an
-- existing database. Applied at startup by alembic_setup.run_manual_sql()
-- after 038, so app.departments already exists.
--
-- The legacy free-text requisitions.department column is kept and only read
-- here to backfill: rows whose text equals a department's name or short code
-- (case-insensitive, trimmed) get that department's id. Unmatched rows stay
-- NULL. Drop the text column in a later migration once nothing reads it.

ALTER TABLE app.requisitions
    ADD COLUMN IF NOT EXISTS department_id uuid;

DO $$
BEGIN
    IF NOT EXISTS (
        SELECT 1 FROM pg_constraint
        WHERE conname = 'fk_requisitions_department_id_departments'
    ) THEN
        ALTER TABLE app.requisitions
            ADD CONSTRAINT fk_requisitions_department_id_departments
            FOREIGN KEY (department_id) REFERENCES app.departments (id);
    END IF;
END $$;

CREATE INDEX IF NOT EXISTS ix_requisitions_department_id
    ON app.requisitions (department_id);

-- Backfill from the legacy text column, if it is still there.
DO $$
BEGIN
    IF EXISTS (
        SELECT 1 FROM information_schema.columns
        WHERE table_schema = 'app'
          AND table_name = 'requisitions'
          AND column_name = 'department'
    ) THEN
        UPDATE app.requisitions r
        SET department_id = d.id
        FROM app.departments d
        WHERE r.department_id IS NULL
          AND lower(btrim(r.department)) IN (lower(d.name), lower(d.short_code));
    END IF;
END $$;