Rectangle.php

<?php

interface RectangleDataGetterInterface
{
    public function getHeight(): int;

    public function getWidth(): int;
}

interface RectangleInterface extends RectangleDataGetterInterface
{
    public function setHeight(int $height);

    public function setWidth(int $width);
}

interface SquareInterface extends RectangleDataGetterInterface
{
    public function setSide(int $side);
}

class Rectangle implements RectangleInterface
{
    private $height;
    private $width;

    public function __construct(int $height, int $width)
    {
        $this->height = $height;
        $this->width = $width;
    }

    public function setHeight(int $height)
    {
        $this->height = $height;
    }

    public function setWidth(int $width)
    {
        $this->width = $width;
    }

    public function getHeight(): int
    {
        return $this->height;
    }

    public function getWidth(): int
    {
        return $this->width;
    }
}

class Square implements SquareInterface
{
    private $side;

    public function __construct(int $side)
    {
        $this->side = $side;
    }

    public function setSide(int $side)
    {
        $this->side = $side;
    }

    public function getHeight(): int
    {
        return $this->side;
    }

    public function getWidth(): int
    {
        return $this->side;
    }
}

class RectangleCalculator
{
    private $rectangle;

    public function __construct(RectangleDataGetterInterface $rectangle)
    {
        $this->rectangle = $rectangle;
    }

    public function getArea(): int
    {
        return $this->rectangle->getWidth() * $this->rectangle->getHeight();
    }
}

$rectangle = new Rectangle(2, 4);
$rectangleCalculator = new RectangleCalculator($rectangle);
echo $rectangleCalculator->getArea() . PHP_EOL;

$square = new Square(3);
$squareCalculator = new RectangleCalculator($square);
echo $squareCalculator->getArea() . PHP_EOL;

$square->setSide(5);
echo $squareCalculator->getArea() . PHP_EOL;