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 itemId = body.itemId as string;
    const quantity = Number(body.quantity);

    if (!itemId || !Number.isFinite(quantity)) {
      return NextResponse.json(
        { error: "itemId and quantity are required." },
        { status: 400 }
      );
    }

    const session = await getServerSession(authOptions);
    const cookieStore = cookies();
    let sessionId = cookieStore.get("sf_session")?.value;
    const createdNew = !sessionId;
    if (!sessionId && !session?.user?.email) {
      return NextResponse.json({ error: "Missing cart session." }, { status: 400 });
    }

    const item = await prisma.cartItem.findUnique({
      where: { id: itemId },
      include: { cart: true },
    });

    if (!item) {
      return NextResponse.json({ error: "Item not found." }, { status: 404 });
    }

    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 });
      }
      if (item.cart.userId !== user.id && item.cart.sessionId !== sessionId) {
        return NextResponse.json({ error: "Item not found." }, { status: 404 });
      }
      if (!sessionId) {
        sessionId = crypto.randomUUID();
        await prisma.cart.update({
          where: { id: item.cartId },
          data: { sessionId },
        });
      }
    } else if (item.cart.sessionId !== sessionId) {
      return NextResponse.json({ error: "Item not found." }, { status: 404 });
    }

    if (quantity <= 0) {
      await prisma.cartItem.delete({ where: { id: itemId } });
      const res = NextResponse.json({ deleted: true });
      if (createdNew && sessionId) {
        res.cookies.set("sf_session", sessionId, {
          httpOnly: true,
          sameSite: "lax",
          path: "/",
        });
      }
      return res;
    }

    const updated = await prisma.cartItem.update({
      where: { id: itemId },
      data: { quantity },
    });

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