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SOLUTION.md

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Sales Taxes Solution

This file explains the solution applied to the Sales Taxes Problem described in the PROBLEM.md file.

Application Implementation

Value Objects

I have identified some Value Object represented by:

  • Category: A basic enum with a list of all product categories.
  • BasicTax: The basic sales tax applicable to all products except the specified categories.
  • ImportDuty: The import duty applicable to imported products.

Entities

I have identified some entities in this problem, so I have implemented the following Entity classes:

  • Product: A Product represented by name, price, category and a flag to indicate if the product has been imported.
  • ShoppingItem: A Shopping Item represented by a Product and by the quantity of such product added in the Shopping Basket.
  • ShoppingBasket: A Shopping Basket represented by a ShoppingItem list in the Shopping Basket.
  • SalesItem: A Sales Item represented by name, quantity, taxes and total price (including tax) of a product for sale.
  • SalesReceipt: A Sales Receipt represented by a Sales Item list of products sold.

Note that Entities are immutable objects, so they cannot be modified after they are created.

Interfaces

I have defined the following interfaces:

  • RoundingInterface: Interface used to round taxes.
  • TaxableInterface: Interface implemented by taxable products.
  • TaxInterface: Interface of a generic tax.

Services

I have implemented three services:

  • TaxEngine: Engine to apply any sales tax (Basic Tax and Import Duty) calculated in a deacoupled way.
  • RoundingUp005: Rounding service that implements the required rounding of taxes.
  • Cashier: Execute the checkout returning a SalesReceipt from a ShoppingBasket.

Exceptions

The application may throw some InvalidArgumentException.

Application

Finally, I have put togheter all little bricks in the index.php file that, as required:

  • includes the list of the predefined ShoppingBasket
  • executes the checkout to generate a SalesReceipt for each ShoppingBasket
  • print the input data ShoppingBasket and the output data SalesReceipt

php public/index.php

INPUT

Input 1:
2 book at 12.49
1 music CD at 14.99
1 chocolate bar at 0.85

Input 2:
1 imported box of chocolates at 10.00
1 imported bottle of perfume at 47.50

Input 3:
1 imported bottle of perfume at 27.99
1 bottle of perfume at 18.99
1 packet of headache pills at 9.75
3 imported box of chocolates at 11.25


OUTPUT

Output 1:
2 book: 24.98
1 music CD: 16.49
1 chocolate bar: 0.85
Sales Taxes: 1.50
Total: 42.32

Output 2:
1 imported box of chocolates: 10.50
1 imported bottle of perfume: 54.65
Sales Taxes: 7.65
Total: 65.15

Output 3:
1 imported bottle of perfume: 32.19
1 bottle of perfume: 20.89
1 packet of headache pills: 9.75
3 imported box of chocolates: 35.55
Sales Taxes: 7.90
Total: 98.38

Application Testing

I have also implemented some unit test using PHPUnit to test all classes (included the exceptions) in the application:

  • tests/ValueObject/CategoryTest.php
  • tests/Entity/ProductTest.php
  • tests/Entity/ShoppingItemTest.php
  • tests/Entity/ShoppingBasketTest.php
  • tests/Entity/SalesItemTest.php
  • tests/Entity/SalesReceiptTest.php
  • tests/Service/RoundingUp005Test.php
  • tests/ApplicationTest.php

The last unit test has the goal to test the correctness of all the example output in the specifications.

./vendor/bin/phpunit --testdox

PHPUnit 9.5.4 by Sebastian Bergmann and contributors.

Runtime:       PHP 8.0.6
Configuration: /var/www/phpunit.xml

Category
 ✔ Name  144 ms
 ✔ Value  1 ms
 ✔ Is equal  23 ms

Product
 ✔ Name  52 ms
 ✔ Price  1 ms
 ✔ Price must be greater than zero  24 ms
 ✔ Category  1 ms
 ✔ Imported  1 ms
 ✔ Is equal  1 ms

Shopping Item
 ✔ Quantity  8 ms
 ✔ Quantity must be greater than zero  1 ms
 ✔ Product  1 ms

Shopping Basket
 ✔ Constructor accept only shopping items  8 ms
 ✔ Shopping items count  13 ms

Sales Item
 ✔ Name  9 ms
 ✔ Quantity  1 ms
 ✔ Quantity must be greater than zero  1 ms
 ✔ Taxes  1 ms
 ✔ Total  1 ms

Sales Receipt
 ✔ Items count  8 ms

Rounding Up005
 ✔ Round  16 ms

Application
 ✔ Receipt 1  59 ms
 ✔ Receipt 2  1 ms
 ✔ Receipt 3  1 ms

Time: 00:00.403, Memory: 6.00 MB