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sales

Instructions

In this exercise a shopping system will have to be created. There will be :

A store that will save all the products in it
A cart that will have items that the client will buy, and a receipt

This store is having a promotion, "Buy three and get one for free" (the free item must be the cheapest). The receipt must not present any value as 0, so the promotion must be a reduction to be applied to all items instead.(see the example)

You will have to implement for the Cart structure the following functions:

new, that will initialize the cart
insert_item, that will receive a reference to Store and a String. Just like the name says you will have to insert the item to the cart
generate_receipt, that returns a vector of sorted floats. This function must generate the receipt just like the example above, using the promotion. Also saving the result in the filed receipt.

Notions

closures

Expected Function

#[derive(Debug, Clone, PartialEq)]
pub struct Store {
    pub products: Vec<(String, f32)>,
}
impl Store {
    pub fn new(products: Vec<(String, f32)>) -> Store {
        Store { products }
    }
}

#[derive(Debug, Clone, PartialEq)]
pub struct Cart {
    // expected public fields
}
impl Cart {
    pub fn new() -> Cart {}
    pub fn insert_item(&mut self, s: &Store, ele: String) {}
    pub fn generate_receipt(&mut self) -> Vec<f32> {}
}

Example

[1.23, 3.12, 23.1] -> the receipt will be [1.17, 2.98, 22.07]

Because 1.17 + 2.98 + 22.07 == 0 + 3.12 + 23.1

This is a percentage calculation, and it can be applied to a set of three items. If the client purchase 9 items, the promotion will be applied, three for free, to all items

[1.23, 23.1, 3.12, 9.75, 1.75, 23.75, 2.75, 1.64, 15.23] -> the receipt will be [1.16, 1.55, 1.65, 2.6, 2.94, 9.2, 14.38, 21.8, 22.42]

[3.12, 9.75, 1.75, 23.75, 2.75, 1.64, 15.23] -> the receipt will be [1.54, 1.65, 2.59, 2.94, 9.18, 14.34, 22.36]

and so on... (hint: Closures is the way)

Usage

Here is a program to test your function,

use sales::*;

fn main() {
    let store = Store::new(vec![
        (String::from("product A"), 1.23),
        (String::from("product B"), 23.1),
        (String::from("product C"), 3.12)]);

    println!("{:?}", store);

    let mut cart = Cart::new();
    cart.insert_item(&store, String::from("product A"));
    cart.insert_item(&store, String::from("product B"));
    cart.insert_item(&store, String::from("product C"));

    println!("{:?}", cart.generate_receipt());

    println!("{:?}", cart);
}

And its output:

$ cargo run
Store { products: [("product A", 1.23), ("product B", 23.1), ("product C", 3.12)] }
[1.17, 2.98, 22.07]
Cart { items: [("product A", 1.23), ("product B", 23.1), ("product C", 3.12)], receipt: [1.17, 2.98, 22.07] }
$

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