Zastosowanie wszystkich poprawek UI i logiki kalkulatora

lib/cart-store.ts

@@ -0,0 +1,68 @@
+import { create } from 'zustand';
+import { persist } from 'zustand/middleware';
+
+export interface CartItem {
+  id: string;
+  slug: string;
+  name: string;
+  brand: string;
+  image: string;
+  price: number;
+  quantity: number;
+}
+
+interface CartState {
+  items: CartItem[];
+  addItem: (item: Omit<CartItem, 'id' | 'quantity'>) => void;
+  removeItem: (id: string) => void;
+  updateQuantity: (id: string, quantity: number) => void;
+  clearCart: () => void;
+  getTotal: () => number;
+  getCount: () => number;
+}
+
+export const useCartStore = create<CartState>()(
+  persist(
+    (set, get) => ({
+      items: [],
+
+      addItem: (newItem) => {
+        set((state) => {
+          const id = newItem.slug;
+          const existing = state.items.find((i) => i.id === id);
+          if (existing) {
+            return {
+              items: state.items.map((i) =>
+                i.id === id ? { ...i, quantity: i.quantity + 1 } : i
+              ),
+            };
+          }
+          return { items: [...state.items, { ...newItem, id, quantity: 1 }] };
+        });
+      },
+
+      removeItem: (id) =>
+        set((state) => ({ items: state.items.filter((i) => i.id !== id) })),
+
+      updateQuantity: (id, quantity) => {
+        if (quantity < 1) return;
+        set((state) => ({
+          items: state.items.map((i) => (i.id === id ? { ...i, quantity } : i)),
+        }));
+      },
+
+      clearCart: () => set({ items: [] }),
+
+      getTotal: () => {
+        const { items } = get();
+        return items.reduce((sum, i) => sum + i.price * i.quantity, 0);
+      },
+
+      getCount: () => {
+        const { items } = get();
+        return items.reduce((sum, i) => sum + i.quantity, 0);
+      },
+    }),
+    { name: 'thermcool-cart' }
+  )
+);