add. Closes #8

store/useSelectedBook.ts

@@ -0,0 +1,58 @@
+import { defineStore } from 'pinia'
+
+interface CartItem {
+  id: number
+  quantity: number
+  summary?: number
+}
+
+export const useSelectedBook = defineStore('selectedBook', {
+  state: () => ({
+    cartQuantities: [] as CartItem[],
+  }),
+  actions: {
+    increment(id: number) {
+      const item = this.cartQuantities.find((i) => i.id === id)
+      if (item && item.quantity < 1) {
+        item.quantity++
+      }
+    },
+    decrement(id: number) {
+      const item = this.cartQuantities.find((i) => i.id === id)
+      if (item) {
+        item.quantity--
+      }
+    },
+    reset(id: number) {
+      const idx = this.cartQuantities.findIndex((i) => i.id === id)
+      if (idx !== -1) {
+        this.cartQuantities.splice(idx, 1)
+      }
+    },
+    addToCart(id: number) {
+      if (!this.cartQuantities.find((i) => i.id === id)) {
+        this.cartQuantities.push({ id, quantity: 1 })
+      }
+    },
+    getQuantity(id: number) {
+      return this.cartQuantities.find((i) => i.id === id)?.quantity || 0
+    },
+  },
+  getters: {
+    getTotalPrice: (state) => (books: { id: number; price: number }[]) => {
+      const selected = state.cartQuantities.filter((i) => i.quantity > 0)
+      if (selected.length === 2) {
+        // Проверяем, что это две разные книги
+        const ids = selected.map((i) => i.id)
+        if (ids[0] !== ids[1]) {
+          return 936
+        }
+      }
+      // Обычная сумма
+      return selected.reduce((sum, item) => {
+        const book = books.find((b) => b.id === item.id)
+        return sum + (book ? book.price * item.quantity : 0)
+      }, 0)
+    },
+  },
+})