Initial OSS scaffold from Songs2VID (pre-strip)

lib/credits.ts

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+/**
+ * Billing / credit constants for Songs2VID hybrid pricing.
+ * Plan enum in DB: FREE | PREMIUM (Pro = €5/mo "starter_5eur").
+ */
+
+export const CREDIT_CURRENCY = "eur";
+
+/** Free monthly allocation */
+export const FREE_MONTHLY_CREDITS = 10;
+
+/** Pro monthly allocation */
+export const PRO_MONTHLY_CREDITS = 50;
+
+/** Free-tier top-up: buyer picks 1–15 credits */
+export const FREE_TOP_UP_MIN = 1;
+export const FREE_TOP_UP_MAX = 15;
+
+/** €0.25 per extra credit */
+export const CREDIT_PRICE_CENTS = 25;
+
+/** @deprecated use FREE_TOP_UP_MAX */
+export const FREE_TOP_UP_CREDITS = FREE_TOP_UP_MAX;
+
+/** @deprecated use creditPurchaseTotalCents(FREE_TOP_UP_MAX) */
+export const FREE_TOP_UP_PRICE_CENTS = FREE_TOP_UP_MAX * CREDIT_PRICE_CENTS;
+
+/** Pro subscription €5 / month */
+export const PRO_PRICE_CENTS = 500;
+
+/** Soft cap on never-expiring extra credits (Pro / legacy storage bound) */
+export const EXTRA_CREDITS_MAX = 1000;
+
+/**
+ * Hard cap on total accumulated credits (monthly remaining + extras).
+ * On renewal, unused + new monthly is trimmed to this threshold.
+ */
+export const MAX_CREDIT_CAP = 30;
+
+/**
+ * Free plan: extras balance cannot exceed 15.
+ * After monthly (10) + extras (≤15) are used, upgrade to Pro is required.
+ */
+export const FREE_EXTRA_CREDITS_MAX = FREE_TOP_UP_MAX;
+
+/** Stripe Tax / Managed Payments  SaaS personal use */
+export const STRIPE_PRODUCT_TAX_CODE = "txcd_10103000";
+
+export const CREDIT_PURCHASE_MIN = FREE_TOP_UP_MIN;
+export const CREDIT_PURCHASE_MAX = FREE_TOP_UP_MAX;
+export const CREDIT_BALANCE_MAX = EXTRA_CREDITS_MAX;
+
+/** Shown in quota UI errors so UpgradeProLink can attach a CTA */
+export const PRO_UPGRADE_REQUIRED_SUFFIX = " Upload up to 50 videos with Pro!";
+
+export function monthlyCreditsForPlan(plan: "FREE" | "PREMIUM"): number {
+  return plan === "PREMIUM" ? PRO_MONTHLY_CREDITS : FREE_MONTHLY_CREDITS;
+}
+
+export function freeExtraCreditsCap(): number {
+  return FREE_EXTRA_CREDITS_MAX;
+}
+
+export function formatEuroFromCents(cents: number): string {
+  const amount = cents / 100;
+  const formatted = amount % 1 === 0 ? String(amount) : amount.toFixed(2);
+  return `€${formatted}`;
+}
+
+export function creditPurchaseTotalCents(credits: number): number {
+  return credits * CREDIT_PRICE_CENTS;
+}
+
+export function formatCreditPrice(credits = 1): string {
+  return formatEuroFromCents(creditPurchaseTotalCents(credits));
+}
+
+export function validateFreeTopUpAmount(
+  credits: number,
+  currentExtraBalance: number,
+  monthlyRemaining = 0,
+): { ok: true; credits: number; amountCents: number } | { ok: false; error: string } {
+  if (!Number.isInteger(credits)) {
+    return { ok: false, error: "Credit amount must be a whole number." };
+  }
+  if (credits < FREE_TOP_UP_MIN || credits > FREE_TOP_UP_MAX) {
+    return {
+      ok: false,
+      error: `You can buy between ${FREE_TOP_UP_MIN} and ${FREE_TOP_UP_MAX} credits per top-up.`,
+    };
+  }
+  if (currentExtraBalance >= FREE_EXTRA_CREDITS_MAX) {
+    return {
+      ok: false,
+      error: `Free plan extras are capped at ${FREE_EXTRA_CREDITS_MAX}. Upgrade to Pro for 50 videos every month.${PRO_UPGRADE_REQUIRED_SUFFIX}`,
+    };
+  }
+  const freeExtraRoom = FREE_EXTRA_CREDITS_MAX - currentExtraBalance;
+  const totalRoom = Math.max(0, MAX_CREDIT_CAP - monthlyRemaining - currentExtraBalance);
+  const room = Math.min(freeExtraRoom, totalRoom);
+  if (room <= 0) {
+    return {
+      ok: false,
+      error: `Your total credit balance cannot exceed ${MAX_CREDIT_CAP}. Upgrade to Pro or use existing credits first.${PRO_UPGRADE_REQUIRED_SUFFIX}`,
+    };
+  }
+  if (credits > room) {
+    return {
+      ok: false,
+      error: `You can buy up to ${room} more credits under the ${MAX_CREDIT_CAP}-credit account cap.`,
+    };
+  }
+  return { ok: true, credits, amountCents: creditPurchaseTotalCents(credits) };
+}