<?php

enum 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; // fine
echo $me->mood()->value;      // tired