Initial work, copied from the Shopify provider

framework/saleor/cart/use-cart.tsx

@@ -0,0 +1,59 @@
+import { useMemo } from 'react'
+import useCommerceCart, {
+  FetchCartInput,
+  UseCart,
+} from '@commerce/cart/use-cart'
+
+import { Cart } from '../types'
+import { SWRHook } from '@commerce/utils/types'
+import { checkoutCreate, checkoutToCart } from '../utils'
+import getCheckoutQuery from '../utils/queries/get-checkout-query'
+
+export default useCommerceCart as UseCart<typeof handler>
+
+export const handler: SWRHook<
+  Cart | null,
+  {},
+  FetchCartInput,
+  { isEmpty?: boolean }
+> = {
+  fetchOptions: {
+    query: getCheckoutQuery,
+  },
+  async fetcher({ input: { cartId: checkoutId }, options, fetch }) {
+    let checkout
+
+    if (checkoutId) {
+      const data = await fetch({
+        ...options,
+        variables: {
+          checkoutId: checkoutId,
+        },
+      })
+      checkout = data.node
+    }
+
+    if (checkout?.completedAt || !checkoutId) {
+      checkout = await checkoutCreate(fetch)
+    }
+
+    return checkoutToCart({ checkout })
+  },
+  useHook: ({ useData }) => (input) => {
+    const response = useData({
+      swrOptions: { revalidateOnFocus: false, ...input?.swrOptions },
+    })
+    return useMemo(
+      () =>
+        Object.create(response, {
+          isEmpty: {
+            get() {
+              return (response.data?.lineItems.length ?? 0) <= 0
+            },
+            enumerable: true,
+          },
+        }),
+      [response]
+    )
+  },
+}