-- A purchase is charged either to a team (a parent product category) or to Pusat.
-- Pusat has no category of its own, so it is stored as a scope rather than a row;
-- which outlet's Pusat it is comes from purchase_orders.outlet_id.
-- team_scope IS NULL means the team was never chosen, which is deliberately
-- distinct from a purchase that belongs to Pusat.
ALTER TABLE purchase_orders
    ADD COLUMN IF NOT EXISTS team_scope VARCHAR(20),
    ADD COLUMN IF NOT EXISTS team_category_id UUID;

ALTER TABLE purchase_orders
    ADD CONSTRAINT fk_purchase_orders_team_category
        FOREIGN KEY (team_category_id) REFERENCES categories(id) ON DELETE RESTRICT;

-- Deleting a category that is still charged on a purchase order must fail rather
-- than silently drop the attribution, hence RESTRICT above and this pairing check.
-- Written as a CASE because an OR chain would evaluate to NULL when team_scope is
-- NULL, and a CHECK only rejects FALSE — a stray team_category_id would slip past.
ALTER TABLE purchase_orders
    ADD CONSTRAINT chk_purchase_orders_team
        CHECK (
            CASE
                WHEN team_scope IS NULL      THEN team_category_id IS NULL
                WHEN team_scope = 'category' THEN team_category_id IS NOT NULL
                WHEN team_scope = 'central'  THEN team_category_id IS NULL
                ELSE false
            END
        );

CREATE INDEX IF NOT EXISTS idx_purchase_orders_team_category_id
    ON purchase_orders(team_category_id);

CREATE INDEX IF NOT EXISTS idx_purchase_orders_team_scope
    ON purchase_orders(team_scope);