import { NextResponse } from "next/server";
import { prisma } from "../../../../lib/prisma";
import { cookies } from "next/headers";
import { getServerSession } from "next-auth";
import { authOptions } from "../../../../lib/auth";

export async function POST(req: Request) {
  try {
    const body = await req.json();
    const slug = body.slug as string;
    const productId = body.productId as string;
    const priceId = body.priceId as string;
    const name = body.name as string;
    const unitAmount = Number(body.unitAmount);
    const currency = body.currency as string;
    const quantity = Number(body.quantity) || 1;

    if (
      !slug ||
      !productId ||
      !priceId ||
      !name ||
      !Number.isFinite(unitAmount) ||
      !currency
    ) {
      return NextResponse.json(
        { error: "Missing required cart fields." },
        { status: 400 }
      );
    }

    const store = await prisma.store.findUnique({ where: { slug } });
    if (!store) {
      return NextResponse.json({ error: "Store not found." }, { status: 404 });
    }

    const session = await getServerSession(authOptions);
    const cookieStore = cookies();
    let sessionId = cookieStore.get("sf_session")?.value;
    const createdNew = !sessionId;
    if (!sessionId) sessionId = crypto.randomUUID();

    const sessionCart = await prisma.cart.findUnique({
      where: { storeId_sessionId: { storeId: store.id, sessionId } },
    });

    let cart;
    if (session?.user?.email) {
      const user = await prisma.user.findUnique({
        where: { email: session.user.email },
      });
      if (!user) {
        return NextResponse.json({ error: "User not found." }, { status: 404 });
      }
      const userCart = await prisma.cart.findUnique({
        where: { storeId_userId: { storeId: store.id, userId: user.id } },
      });

      if (!userCart) {
        if (sessionCart) {
          cart = await prisma.cart.update({
            where: { id: sessionCart.id },
            data: { userId: user.id },
          });
        } else {
          cart = await prisma.cart.create({
            data: { storeId: store.id, userId: user.id, sessionId },
          });
        }
      } else if (sessionCart && sessionCart.id !== userCart.id) {
        const sessionItems = await prisma.cartItem.findMany({
          where: { cartId: sessionCart.id },
        });
        for (const item of sessionItems) {
          const existing = await prisma.cartItem.findFirst({
            where: { cartId: userCart.id, priceId: item.priceId },
          });
          if (existing) {
            await prisma.cartItem.update({
              where: { id: existing.id },
              data: { quantity: existing.quantity + item.quantity },
            });
          } else {
            await prisma.cartItem.create({
              data: {
                cartId: userCart.id,
                productId: item.productId,
                priceId: item.priceId,
                name: item.name,
                unitAmount: item.unitAmount,
                currency: item.currency,
                quantity: item.quantity,
              },
            });
          }
        }
        await prisma.cart.delete({ where: { id: sessionCart.id } });
        cart = await prisma.cart.update({
          where: { id: userCart.id },
          data: { sessionId },
        });
      } else if (userCart.sessionId !== sessionId) {
        cart = await prisma.cart.update({
          where: { id: userCart.id },
          data: { sessionId },
        });
      } else {
        cart = userCart;
      }
    } else {
      cart =
        sessionCart ??
        (await prisma.cart.create({ data: { storeId: store.id, sessionId } }));
    }

    const existing = await prisma.cartItem.findFirst({
      where: { cartId: cart.id, priceId },
    });

    const item = existing
      ? await prisma.cartItem.update({
          where: { id: existing.id },
          data: { quantity: existing.quantity + quantity },
        })
      : await prisma.cartItem.create({
          data: {
            cartId: cart.id,
            productId,
            priceId,
            name,
            unitAmount,
            currency,
            quantity,
          },
        });

    const res = NextResponse.json({ item });
    if (createdNew) {
      res.cookies.set("sf_session", sessionId, {
        httpOnly: true,
        sameSite: "lax",
        path: "/",
      });
    }
    return res;
  } catch (err: any) {
    return NextResponse.json(
      { error: err?.message || "Failed to add to cart." },
      { status: 500 }
    );
  }
}