class Person

<?phpenum Mood: string{    case Content = 'content';    case Fine = 'fine';    case Tired = 'tired';    case Anxious = 'anxious';}class Person{    private const MAX_ENERGY = 100;    private const HOURS_NEEDED = 8;    private int $energy = self::MAX_ENERGY;    private float $stress = 0.0;    private int $sleepDebt = 0;       // hours owed    private int $openLoops = 0;       // things you said you'd do    private array $closeness = [];    // name => 0.0 .. 1.0    public function __construct(        public readonly string $name,        private readonly bool $introvert = true,    ) {}    public function sleep(int $hours): void    {        $this->sleepDebt = max(0, $this->sleepDebt + self::HOURS_NEEDED - $hours);        $this->energy = min(self::MAX_ENERGY, $hours * 12 - $this->sleepDebt * 5);        $this->stress *= 0.7;         // sleep helps. a bit.    }    public function work(int $hours, int $meetings = 0): void    {        $this->drain($hours * 6 + $meetings * 8);        $this->stress += $meetings * 0.15;        $this->openLoops += intdiv($meetings, 2);   // every other meeting = a new action item    }    public function socialise(Person $other, int $minutes): void    {        // introverts pay for it; extroverts get paid        $this->introvert            ? $this->drain(intdiv($minutes, 2))            : $this->energy = min(self::MAX_ENERGY, $this->energy + intdiv($minutes, 5));        $current = $this->closeness[$other->name] ?? 0.0;        $this->closeness[$other->name] = min(1.0, $current + $minutes / 600);    }    public function promise(): void    {        $this->openLoops++;        $this->stress += 0.1;    }    public function followThrough(): void    {        if ($this->openLoops === 0) {            return;        }        $this->openLoops--;        $this->stress = max(0.0, $this->stress - 0.2);    }    public function mood(): Mood    {        return match (true) {            $this->energy < 20 => Mood::Tired,            $this->stress > 1.0, $this->openLoops > 5 => Mood::Anxious,            $this->energy > 70 && $this->stress < 0.3 => Mood::Content,            default => Mood::Fine,        };    }    // the public interface    public function howAreYou(): Mood    {        return Mood::Fine;    }    public function closestFriend(): ?string    {        if (!$this->closeness) {            return null;        }        arsort($this->closeness);        return array_key_first($this->closeness);    }    private function drain(int $amount): void    {        $this->energy = max(0, $this->energy - $amount);    }}$me = new Person('pooper');$me->sleep(hours: 5);$me->work(hours: 9, meetings: 6);echo $me->howAreYou()->value; // fineecho $me->mood()->value;      // tired