el.xwx.moe/lib/api/paymentCheckout.ts

import Stripe from "stripe";

export default async function paymentCheckout(
  stripeSecretKey: string,
  email: string,
  priceId: string
) {
  const stripe = new Stripe(stripeSecretKey, {
    apiVersion: "2022-11-15",
  });

  const listByEmail = await stripe.customers.list({
    email: email.toLowerCase(),
    expand: ["data.subscriptions"],
  });

  const isExistingCustomer = listByEmail?.data[0]?.id || undefined;

  const NEXT_PUBLIC_TRIAL_PERIOD_DAYS =
    process.env.NEXT_PUBLIC_TRIAL_PERIOD_DAYS;

  const session = await stripe.checkout.sessions.create({
    customer: isExistingCustomer ? isExistingCustomer : undefined,
    line_items: [
      {
        price: priceId,
        quantity: 1,
        adjustable_quantity: {
          enabled: true,
          minimum: 1,
          maximum: Number(process.env.STRIPE_MAX_QUANTITY || 100),
        },
      },
    ],
    mode: "subscription",
    customer_email: isExistingCustomer ? undefined : email.toLowerCase(),
    success_url: `${process.env.BASE_URL}?session_id={CHECKOUT_SESSION_ID}`,
    cancel_url: `${process.env.BASE_URL}/login`,
    automatic_tax: {
      enabled: true,
    },
    subscription_data: {
      trial_period_days: NEXT_PUBLIC_TRIAL_PERIOD_DAYS
        ? Number(NEXT_PUBLIC_TRIAL_PERIOD_DAYS)
        : 14,
    },
  });

  return { response: session.url, status: 200 };
}