POS Scanner

calculator.php

<?php
declare(strict_types=1);

namespace Src\PackItems;

final class Calculator
{
    /**
     * @var Item[]
     */
    private $items;
    /**
     * @var array
     */
    private $pricing;

    private function __construct(array $items, array $pricing)
    {
        $this->items = $items;
        $this->pricing = $pricing;
    }

    /**
     * @return Calculator
     */
    public static function empty(): Calculator
    {
        return new static([], []);
    }

    /**
     * @param Item $item
     */
    public function scan(Item $item): void
    {
        foreach ($this->items as $existingItem) {
            if ($existingItem->equals($item)) {
                $existingItem->setQuantity($existingItem->getQuantity() + $item->getQuantity());

                return;
            }
        }
        if(array_key_exists($item->getCode(), $this->pricing)){
            $item->withPackPrice($this->pricing[$item->getCode()]);
        }
        $this->items[] = $item;
    }

    /**
     * @return float
     */
    public function total(): float
    {
        $total = 0;
        foreach ($this->items as $item) {
            $total += $item->getTotal();
        }

        return $total / 100;
    }

    /**
     * @param array $pricing
     *
     * @return Calculator
     */
    public function setPricing(array $pricing): Calculator
    {
        $this->pricing = $pricing;

        return $this;
    }
}

Item.php

<?php
declare(strict_types=1);

namespace Src\PackItems;

final class Item
{
    /**
     * @var int
     */
    private $price;
    /**
     * @var int
     */
    private $quantity;
    /**
     * @var array
     */
    private $packPrice;
    /**
     * @var string
     */
    private $code;

    private function __construct(string $code, int $price, int $quantity, array $packPrice)
    {
        $this->code = $code;
        $this->price = $price;
        $this->quantity = $quantity;
        $this->packPrice = $packPrice;
    }

    /**
     * @param string $code
     * @param int $price
     *
     * @return Item
     */
    public static function fromBasic(string $code, int $price)
    {
        return new static($code, $price, 1, []);
    }

    /**
     * @return int
     */
    public function getQuantity(): int
    {
        return $this->quantity;
    }

    /**
     * @param Item $item
     *
     * @return bool
     */
    public function equals(Item $item): bool
    {
        return $this->code === $item->getCode();
    }

    /**
     * @return float
     */
    public function getTotal(): float
    {
        if (!count($this->packPrice)) {
            return $this->quantity * $this->price;
        }
        $packs = array_keys($this->packPrice);
        $minPack = min($packs);
        if ($this->quantity < $minPack) {
            return $this->quantity * $this->price;
        }
        $totalPrice = 0;
        $quantity = $this->quantity;
        foreach ($this->packPrice as $packQuantity => $packPrice) {
            if ($quantity < $packQuantity) {
                break;
            }
            $totalPrice += $packQuantity * $packPrice;
            $quantity -= $packQuantity;
        }
        $totalPrice += $quantity * $this->price;

        return $totalPrice;
    }

    /**
     * @return string
     */
    public function getCode(): string
    {
        return $this->code;
    }

    /**
     * @param int $quantity
     */
    public function setQuantity(int $quantity): void
    {
        $this->quantity = $quantity;
    }

    /**
     * @param array $packPrice
     *
     * @return Item
     */
    public function withPackPrice(array $packPrice): Item
    {
        $this->packPrice = $packPrice;

        return $this;
    }
}

Test.php

<?php
declare(strict_types=1);

namespace Tests\Unit;

use Src\PackItems\Calculator;
use Src\PackItems\Item;
use Tests\TestCase;

class PackItems extends TestCase
{
    public function testFirst(){
        $calculator = Calculator::empty()
            ->setPricing([
                'A' => [4 => 175],
                'C' => [6 => 100]
            ]);
        $items = [
            Item::fromBasic('A', 200),
            Item::fromBasic('B', 1200),
            Item::fromBasic('C', 125),
            Item::fromBasic('D', 15),
            Item::fromBasic('A', 200),
            Item::fromBasic('B', 1200),
            Item::fromBasic('A', 200),
            Item::fromBasic('A', 200),
        ];
        foreach($items as $item){
            $calculator->scan($item);
        }
        $this->assertEquals(32.4, $calculator->total());
    }

    public function testSecond(){
        $items = [
            Item::fromBasic('C', 125),
            Item::fromBasic('C', 125),
            Item::fromBasic('C', 125),
            Item::fromBasic('C', 125),
            Item::fromBasic('C', 125),
            Item::fromBasic('C', 125),
            Item::fromBasic('C', 125),
        ];
        $calculator = Calculator::empty()
            ->setPricing([
                'C' => [6 => 100]
            ]);
        foreach($items as $item){
            $calculator->scan($item);
        }
        $this->assertEquals(7.25, $calculator->total());
    }

    public function testThird(){
        $items = [
            Item::fromBasic('A', 200),
            Item::fromBasic('B', 1200),
            Item::fromBasic('C', 125),
            Item::fromBasic('D', 15),
        ];
        $calculator = Calculator::empty()
            ->setPricing([
                'A' => [4 => 175],
                'C' => [6 => 100]
            ]);
        foreach($items as $item){
            $calculator->scan($item);
        }
        $this->assertEquals(15.4, $calculator->total());
    }

    public function testFourth()
    {
        $items = [
            Item::fromBasic('A', 200),
            Item::fromBasic('A', 200),
            Item::fromBasic('A', 200),
            Item::fromBasic('A', 200),
            Item::fromBasic('A', 200),
        ];
        $calculator = Calculator::empty()
            ->setPricing([
                'A' => [4 => 175]
            ]);
        foreach($items as $item){
            $calculator->scan($item);
        }
        $this->assertEquals(((175*4) + 200) / 100, $calculator->total());
    }
}