-- Cancel + supersede: a new terminal CANCELLED status, cancel metadata, and a
-- self-referential supersede link (cancelled PO -> the existing PO that replaces it).
ALTER TYPE "POStatus" ADD VALUE 'CANCELLED';
ALTER TYPE "ActionType" ADD VALUE 'CANCELLED';
ALTER TYPE "ActionType" ADD VALUE 'SUPERSEDED';

ALTER TABLE "PurchaseOrder" ADD COLUMN "cancelledAt" TIMESTAMP(3);
ALTER TABLE "PurchaseOrder" ADD COLUMN "cancellationReason" TEXT;
ALTER TABLE "PurchaseOrder" ADD COLUMN "supersededById" TEXT;

ALTER TABLE "PurchaseOrder" ADD CONSTRAINT "PurchaseOrder_supersededById_fkey"
  FOREIGN KEY ("supersededById") REFERENCES "PurchaseOrder"("id") ON DELETE SET NULL ON UPDATE CASCADE;