Challenge: Shop orders processing
Today I have for you this exercise that I already presented in the Functional Kotlin book and online course. The task is not easy, but it is a solid practice of some essential collection processing functions. The task is to implement the following functions for processing shop orders:
getWaitingCustomersthat returns the list of customers who ordered products that have not been delivered yet.countProductSalesthat returns the number of times a given product was ordered.getWaitingCustomersthat returns the list of customers who made orders with total price greater than or equal to the given amount.
Here is a playground you can use to implement and test your solution. Use "run" button to start unit tests. To see them, use "plus".
import org.junit.Test
import kotlin.test.assertEquals
data class Shop(val name: String, val customers: List<Customer>)
data class Customer(val name: String, val city: City, val orders: List<Order>)
data class Order(val products: List<Product>, val isDelivered: Boolean)
data class Product(val name: String, val price: Double)
data class City(val name: String)
//sampleStart
// Get customers with undelivered products
fun Shop.getWaitingCustomers(): List<Customer> = TODO()
// Return the number of times the given product was ordered.
// Note: a customer may order the same product for several times.
fun Shop.countProductSales(product: Product): Int = TODO()
// Get customers who paid at least `minAmount`
fun Shop.getCustomers(minAmount: Double): List<Customer> = TODO()
//sampleEnd
class ShopFunctionsTests {
@Test
fun `getWaitingCustomers should get customers with any delivered order`() {
// given
val shop = Shop(
name = "Test shop",
customers = listOf(
Customer(
name = "Customer 1",
city = City("City 1"),
orders = listOf(
Order(
products = listOf(
Product("Product 1", 1.0),
Product("Product 2", 2.0),
),
isDelivered = true,
),
Order(
products = listOf(
Product("Product 3", 3.0),
Product("Product 4", 4.0),
),
isDelivered = false,
),
),
),
Customer(
name = "Customer 2",
city = City("City 2"),
orders = listOf(
Order(
products = listOf(
Product("Product 5", 5.0),
Product("Product 6", 6.0),
),
isDelivered = true,
),
Order(
products = listOf(
Product("Product 7", 7.0),
Product("Product 8", 8.0),
),
isDelivered = true,
),
),
),
),
)
// when
val result = shop.getWaitingCustomers()
// then
val expected = listOf(
Customer(
name = "Customer 1",
city = City("City 1"),
orders = listOf(
Order(
products = listOf(
Product("Product 1", 1.0),
Product("Product 2", 2.0),
),
isDelivered = true,
),
Order(
products = listOf(
Product("Product 3", 3.0),
Product("Product 4", 4.0),
),
isDelivered = false,
),
),
),
)
assertEquals(expected, result)
}
@Test
fun `getWaitingCustomers should not return customers with no orders`() {
// given
val shop = Shop(
name = "Test shop",
customers = listOf(
Customer(
name = "Customer 1",
city = City("City 1"),
orders = listOf(
Order(
products = listOf(
Product("Product 1", 1.0),
Product("Product 2", 2.0),
),
isDelivered = true,
),
Order(
products = listOf(
Product("Product 3", 3.0),
Product("Product 4", 4.0),
),
isDelivered = false,
),
),
),
Customer(
name = "Customer 2",
city = City("City 2"),
orders = listOf(),
),
),
)
// when
val result = shop.getWaitingCustomers()
// then
val expected = listOf(
Customer(
name = "Customer 1",
city = City("City 1"),
orders = listOf(
Order(
products = listOf(
Product("Product 1", 1.0),
Product("Product 2", 2.0),
),
isDelivered = true,
),
Order(
products = listOf(
Product("Product 3", 3.0),
Product("Product 4", 4.0),
),
isDelivered = false,
),
),
),
)
assertEquals(expected, result)
}
@Test
fun `getWaitingCustomers should not return customers all orders delivered`() {
// given
val shop = Shop(
name = "Test shop",
customers = listOf(
Customer(
name = "Customer 1",
city = City("City 1"),
orders = listOf(
Order(
products = listOf(
Product("Product 1", 1.0),
Product("Product 2", 2.0),
),
isDelivered = true,
),
Order(
products = listOf(
Product("Product 3", 3.0),
Product("Product 4", 4.0),
),
isDelivered = true,
),
),
),
Customer(
name = "Customer 2",
city = City("City 2"),
orders = listOf(
Order(
products = listOf(
Product("Product 5", 5.0),
Product("Product 6", 6.0),
),
isDelivered = true,
),
Order(
products = listOf(
Product("Product 7", 7.0),
Product("Product 8", 8.0),
),
isDelivered = true,
),
),
),
),
)
// when
val result = shop.getWaitingCustomers()
// then
assertEquals(listOf(), result)
}
@Test
fun `countProductSales should count repeating sales`() {
// given
val p1 = Product("Product 1", 1.0)
val p2 = Product("Product 2", 2.0)
val p3 = Product("Product 3", 3.0)
val shop = Shop(
name = "Test shop",
customers = listOf(
Customer(
name = "Customer 1",
city = City("City 1"),
orders = listOf(
Order(
products = listOf(p1, p2),
isDelivered = true,
),
Order(
products = listOf(p1, p3),
isDelivered = false,
),
),
),
Customer(
name = "Customer 2",
city = City("City 2"),
orders = listOf(
Order(
products = listOf(p1, p1),
isDelivered = true,
),
Order(
products = listOf(p2, p3),
isDelivered = true,
),
),
),
),
)
// then
assertEquals(4, shop.countProductSales(p1))
assertEquals(2, shop.countProductSales(p2))
assertEquals(2, shop.countProductSales(p3))
}
@Test
fun `countProductSales should count sales with exactly the same product`() {
// given
val shop = Shop(
name = "Test shop",
customers = listOf(
Customer(
name = "Customer 1",
city = City("City 1"),
orders = listOf(
Order(
products = listOf(Product("Product 2", 1.0), Product("Product 1", 2.0)),
isDelivered = true,
),
),
),
),
)
// then
assertEquals(0, shop.countProductSales(Product("Product 1", 1.0)))
assertEquals(1, shop.countProductSales(Product("Product 2", 1.0)))
assertEquals(1, shop.countProductSales(Product("Product 1", 2.0)))
assertEquals(0, shop.countProductSales(Product("Product 2", 2.0)))
}
@Test
fun `getCustomers should get customers with orders with total price greater than minAmount`() {
// given
val p1 = Product("Product 1", 1.0)
val p2 = Product("Product 2", 2.0)
val p3 = Product("Product 3", 3.0)
val p4 = Product("Product 4", 4.0)
val p5 = Product("Product 5", 5.0)
val p6 = Product("Product 6", 6.0)
val p7 = Product("Product 7", 7.0)
val p8 = Product("Product 8", 8.0)
val c1 = Customer(
name = "Customer 1",
city = City("City 1"),
orders = listOf(
Order(
products = listOf(p1, p2),
isDelivered = true,
),
Order(
products = listOf(p1, p3),
isDelivered = false,
),
),
)
val c2 = Customer(
name = "Customer 2",
city = City("City 2"),
orders = listOf(
Order(
products = listOf(p1, p1),
isDelivered = true,
),
Order(
products = listOf(p2, p3),
isDelivered = true,
),
),
)
val c3 = Customer(
name = "Customer 3",
city = City("City 3"),
orders = listOf(
Order(
products = listOf(p4, p5),
isDelivered = true,
),
Order(
products = listOf(p6, p7),
isDelivered = true,
),
),
)
val c4 = Customer(
name = "Customer 4",
city = City("City 4"),
orders = listOf(
Order(
products = listOf(p8, p8),
isDelivered = true,
),
),
)
val shop = Shop(
name = "Test shop",
customers = listOf(c1, c2, c3, c4),
)
// then
assertEquals(listOf(c1, c2, c3, c4), shop.getCustomers(0.0))
assertEquals(listOf(c3, c4), shop.getCustomers(10.0))
assertEquals(listOf(c3), shop.getCustomers(20.0))
assertEquals(listOf(), shop.getCustomers(30.0))
}
}
I decided I wouldn't feel good showing you the solution. It can be found at the end of the book Functional Kotlin, and in the course Functional Kotlin, but here it would be just too easy to see it and copy it. I want you to try to solve it yourself. If you have any questions, feel free to ask them in the comments below. You can also send a Tweet to me @marcinmoskala. I will be happy to help you. If you managed to solve this exercise, feel free to share it with others. I will be happy to see your solutions. Good luck and have fun!
, an official JetBrains partner for Kotlin training, author of the books [Effective Kotlin](https://leanpub.com/effectivekotlin/), [Kotlin Coroutines](https://kt.academy/book/coroutines), [Functional Kotlin](https://leanpub.com/kotlin_functional/) and [Android Development with Kotlin](https://www.packtpub.com/product/android-development-with-kotlin/9781787123687). He is also the main author of [the biggest medium publication about Kotlin](https://blog.kotlin-academy.com) and a speaker invited to [many programming conferences](https://www.youtube.com/results?search_query=marcin+moska%C5%82a).](https://lh3.googleusercontent.com/a-/AOh14GgT-nGHTlbxHpiPyUUhgruiheIEyBVEsCDWNdW0xA=s400-c)