refactor(subscription): tighten payment flow boundaries

src/app/subscription/subscription-screen.helpers.ts

@@ -64,3 +64,61 @@ export function toCoinsOfferPlanView(plan: PaymentPlan): CoinsOfferPlanView {
     currency: formatCoinCurrency(plan.currency),
   };
 }
+
+export function toVipOfferPlanViews(
+  plans: readonly PaymentPlan[],
+): VipOfferPlanView[] {
+  return plans.filter(isVipPlan).slice(0, 3).map(toVipOfferPlanView);
+}
+
+export function toCoinsOfferPlanViews(
+  plans: readonly PaymentPlan[],
+): CoinsOfferPlanView[] {
+  return plans.filter(isCreditPlan).map(toCoinsOfferPlanView);
+}
+
+export function findSelectedSubscriptionPlan(input: {
+  canSubscribeVip: boolean;
+  selectedPlanId: string;
+  vipPlans: readonly VipOfferPlanView[];
+  coinPlans: readonly CoinsOfferPlanView[];
+}): VipOfferPlanView | CoinsOfferPlanView | null {
+  const plans = input.canSubscribeVip
+    ? [...input.vipPlans, ...input.coinPlans]
+    : input.coinPlans;
+  return plans.find((plan) => plan.id === input.selectedPlanId) ?? null;
+}
+
+export function getDefaultSubscriptionPlanId(input: {
+  canSubscribeVip: boolean;
+  selectedPlanId: string;
+  status: string;
+  isLoadingPlans: boolean;
+  selectedPlan: VipOfferPlanView | CoinsOfferPlanView | null;
+  vipPlans: readonly VipOfferPlanView[];
+  coinPlans: readonly CoinsOfferPlanView[];
+}): string | null {
+  if (input.canSubscribeVip) {
+    const firstVipPlanId = input.vipPlans[0]?.id ?? "";
+    const hasSelectedVipPlan = input.vipPlans.some(
+      (plan) => plan.id === input.selectedPlanId,
+    );
+    const hasSelectedCoinsPlan = input.coinPlans.some(
+      (plan) => plan.id === input.selectedPlanId,
+    );
+    const canSelectPlan =
+      firstVipPlanId.length > 0 &&
+      (input.status === "ready" ||
+        input.status === "paid" ||
+        input.status === "failed");
+
+    if (!canSelectPlan || hasSelectedVipPlan || hasSelectedCoinsPlan) {
+      return null;
+    }
+    return firstVipPlanId;
+  }
+
+  if (input.isLoadingPlans || input.coinPlans.length === 0) return null;
+  if (input.selectedPlan !== null) return null;
+  return input.coinPlans[0]?.id ?? null;
+}