Kurs PHP 8.4 w praktyce - czym jest SOLID

<?php
interface ShapeContract
{
    public float $area { get; }
}
interface CalculatorContract
{
    public function calculate(): float;
}
interface TextContract
{
    public function text(): string;
}
interface JsonContract
{
    public function json(): string;
}
class Square implements ShapeContract
{
    public function __construct(private readonly int $length){}
    public float $area {
        get => $this->length * $this->length;
    }
}
class Circle implements ShapeContract
{
    public function __construct(private readonly int $radius){}
    public float $area {
        get => $this->radius * $this->radius * pi();
    }
}

readonly class AreaCalculator implements  CalculatorContract
{
    /**
     * @param array $shapes
     */
    public function __construct(protected array $shapes)
    {
    }
    public function calculate(): float
    {
        $data = array_map(fn(ShapeContract $shape) =>
        $shape->area, $this->shapes);
        return array_sum($data);
    }
}

readonly class BigAreaCalculator extends AreaCalculator
{
    public function calculate(): float
    {
        $initial = parent::calculate();
    //some additional logic and filters like not less than
        return $initial;
    }
}
readonly class SumCalculatorOutputter implements TextContract, JsonContract
{
    public function __construct(private CalculatorContract $calculator){}
    public function text(): string
    {
        return "The sum of the areas of the shapes is: " . $this->calculator->calculate();
    }
    public function json(): string
    {
        return json_encode(['sum' => $this->calculator->calculate()]);
    }
}