-- Additive only: existing identifiers and both old counters and drafts stay intact.
CREATE TABLE "business_number_policies" (
  "version" INTEGER PRIMARY KEY CHECK ("version" = 2),
  "effective_at" TIMESTAMP(3) NOT NULL,
  "enabled" BOOLEAN NOT NULL DEFAULT false,
  "updated_at" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
  "updated_by" UUID NOT NULL,
  "reference" TEXT NOT NULL
);
CREATE TABLE "business_number_counters" (
  "key" TEXT PRIMARY KEY,
  "current_number" BIGINT NOT NULL DEFAULT 0 CHECK ("current_number" >= 0),
  "updated_at" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP
);
ALTER TABLE "purchase_requests" ADD COLUMN "numbering_version" INTEGER NOT NULL DEFAULT 1
  CHECK ("numbering_version" IN (1, 2));
-- No INSERT into policy; activation is a separate, explicitly authorized operation.

-- Keep the original eligibility and issued high-water durable across rollback or
-- accidental administrative resets. A pause changes only policy.enabled.
CREATE FUNCTION guard_business_numbering_history() RETURNS trigger AS $$
BEGIN
  IF TG_OP = 'DELETE' THEN
    RAISE EXCEPTION 'business numbering history cannot be deleted' USING ERRCODE = '23514';
  END IF;
  IF TG_TABLE_NAME = 'business_number_policies' THEN
    IF NEW.version <> OLD.version OR NEW.effective_at <> OLD.effective_at THEN
      RAISE EXCEPTION 'business numbering activation is immutable' USING ERRCODE = '23514';
    END IF;
  ELSIF TG_TABLE_NAME = 'business_number_counters' THEN
    IF NEW.key <> OLD.key OR NEW.current_number < OLD.current_number THEN
      RAISE EXCEPTION 'business numbering high-water cannot decrease' USING ERRCODE = '23514';
    END IF;
  END IF;
  RETURN NEW;
END;
$$ LANGUAGE plpgsql;
CREATE TRIGGER business_number_policy_history BEFORE UPDATE OR DELETE ON business_number_policies
  FOR EACH ROW EXECUTE FUNCTION guard_business_numbering_history();
CREATE TRIGGER business_number_counter_history BEFORE UPDATE OR DELETE ON business_number_counters
  FOR EACH ROW EXECUTE FUNCTION guard_business_numbering_history();
CREATE FUNCTION guard_purchase_numbering_version() RETURNS trigger AS $$
BEGIN
  IF NEW.numbering_version <> OLD.numbering_version THEN
    RAISE EXCEPTION 'purchase numbering eligibility is immutable' USING ERRCODE = '23514';
  END IF;
  RETURN NEW;
END;
$$ LANGUAGE plpgsql;
CREATE TRIGGER purchase_numbering_version BEFORE UPDATE OF numbering_version ON purchase_requests
  FOR EACH ROW EXECUTE FUNCTION guard_purchase_numbering_version();