구독 결제 연동: Stripe

npm install stripe @stripe/stripe-js

STRIPE_SECRET_KEY=sk_test_...
NEXT_PUBLIC_STRIPE_PUBLISHABLE_KEY=pk_test_...
STRIPE_WEBHOOK_SECRET=whsec_...

// app/api/checkout/route.ts
import Stripe from 'stripe';
import { NextRequest, NextResponse } from 'next/server';

const stripe = new Stripe(process.env.STRIPE_SECRET_KEY!);

export async function POST(req: NextRequest) {
  const { priceId, userId } = await req.json();

  const session = await stripe.checkout.sessions.create({
    mode: 'subscription',
    payment_method_types: ['card'],
    line_items: [{ price: priceId, quantity: 1 }],
    success_url: `${process.env.NEXT_PUBLIC_URL}/dashboard?success=true`,
    cancel_url: `${process.env.NEXT_PUBLIC_URL}/pricing?canceled=true`,
    customer_email: undefined,
    metadata: { userId },
    // 한국 결제 추가 (Stripe Korea)
    payment_method_options: {
      card: { request_three_d_secure: 'any' },
    },
  });

  return NextResponse.json({ url: session.url });
}

'use client';
import { loadStripe } from '@stripe/stripe-js';

const stripePromise = loadStripe(process.env.NEXT_PUBLIC_STRIPE_PUBLISHABLE_KEY!);

export function SubscribeButton({ priceId }: { priceId: string }) {
  const handleClick = async () => {
    const res = await fetch('/api/checkout', {
      method: 'POST',
      body: JSON.stringify({ priceId, userId: 'current-user-id' }),
    });
    const { url } = await res.json();
    window.location.href = url;  // Stripe Checkout으로 리다이렉트
  };

  return <button onClick={handleClick}>구독하기</button>;
}

// app/api/webhooks/stripe/route.ts
import Stripe from 'stripe';
import { headers } from 'next/headers';

const stripe = new Stripe(process.env.STRIPE_SECRET_KEY!);

export async function POST(req: Request) {
  const body = await req.text();
  const sig = (await headers()).get('stripe-signature')!;

  let event: Stripe.Event;
  try {
    event = stripe.webhooks.constructEvent(body, sig, process.env.STRIPE_WEBHOOK_SECRET!);
  } catch (err) {
    return new Response('Webhook signature verification failed', { status: 400 });
  }

  switch (event.type) {
    case 'checkout.session.completed': {
      const session = event.data.object;
      // 사용자 DB에 구독 활성화 표시
      await activateSubscription(session.metadata!.userId, session.subscription as string);
      break;
    }
    case 'customer.subscription.deleted': {
      const sub = event.data.object;
      await deactivateSubscription(sub.id);
      break;
    }
    case 'invoice.payment_failed': {
      // 결제 실패 → 사용자에게 이메일
      await sendPaymentFailedEmail(event.data.object.customer_email!);
      break;
    }
  }

  return new Response('ok', { status: 200 });
}

// 플랜 변경
async function changePlan(subscriptionId: string, newPriceId: string) {
  const subscription = await stripe.subscriptions.retrieve(subscriptionId);
  await stripe.subscriptions.update(subscriptionId, {
    items: [{ id: subscription.items.data[0].id, price: newPriceId }],
    proration_behavior: 'create_prorations',  // 비율 정산
  });
}

// 해지 (다음 결제일까지 유지)
async function cancelAtPeriodEnd(subscriptionId: string) {
  await stripe.subscriptions.update(subscriptionId, {
    cancel_at_period_end: true,
  });
}