import { type NextRequest, NextResponse } from "next/server";
import { z } from "zod";
import { auth } from "@/app/(auth)/auth";
import { getStripePriceIdForPlan, isPaidBillingPlanId, type PaidBillingPlanId } from "@/lib/billing/plans";
import { createStripeCheckoutSession, StripeRequestError } from "@/lib/billing/stripe";

const checkoutSchema = z.object({
  planId: z.string(),
});

function getExternalBase(request: NextRequest) {
  return (
    process.env.AUTH_URL ??
    `${request.nextUrl.protocol}//${request.headers.get("host") ?? request.nextUrl.host}`
  );
}

export async function POST(request: NextRequest) {
  try {
    const session = await auth();

    if (!session?.user?.id || !session.user.email) {
      return NextResponse.json({ error: "Unauthorized" }, { status: 401 });
    }

    if (session.user.type === "guest") {
      return NextResponse.json({ error: "Guest user cannot checkout" }, { status: 403 });
    }

    const parsed = checkoutSchema.safeParse(await request.json());

    if (!parsed.success || !isPaidBillingPlanId(parsed.data.planId)) {
      return NextResponse.json({ error: "Invalid plan ID" }, { status: 400 });
    }

    const planId = parsed.data.planId as PaidBillingPlanId;
    const stripeSecretKey = process.env.STRIPE_SECRET_KEY;
    const priceId = getStripePriceIdForPlan(planId);

    if (!stripeSecretKey || !priceId) {
      return NextResponse.json(
        { error: "Billing is not configured. Missing Stripe keys or plan price ID." },
        { status: 503 }
      );
    }

    const baseUrl = getExternalBase(request);
    const successUrl = new URL(`/lovart/pricing?checkout=success&plan=${planId}`, baseUrl).toString();
    const cancelUrl = new URL(`/lovart/pricing?checkout=cancelled&plan=${planId}`, baseUrl).toString();

    const checkoutSession = await createStripeCheckoutSession({
      secretKey: stripeSecretKey,
      priceId,
      userId: session.user.id,
      email: session.user.email,
      planId,
      successUrl,
      cancelUrl,
    });

    return NextResponse.json({
      id: checkoutSession.id,
      url: checkoutSession.url,
    });
  } catch (error) {
    if (error instanceof StripeRequestError) {
      return NextResponse.json({ error: error.message }, { status: error.status });
    }

    console.error("[Billing Checkout API] Error:", error);
    return NextResponse.json({ error: "Failed to create checkout session" }, { status: 500 });
  }
}