<?php

declare(strict_types=1);

namespace App\Support;

use App\Models\User;
use Illuminate\Database\Eloquent\Model;
use Illuminate\Support\Collection;
use Illuminate\Support\Facades\Cache;

/**
 * Who else has a record's edit screen open right now.
 *
 * Advisory, not authoritative — there is no signal at all for "closed the
 * tab", so presence really means "opened this within the last few minutes",
 * which fades out on its own once nobody touches the screen again. That
 * heuristic is the right shape for the problem: knowing that two people are
 * mid-edit matters; an exact headcount does not.
 */
final class Presence
{
    /**
     * How long somebody stays "here" after they were last seen. Long enough
     * to survive reading a long field without typing; short enough that a
     * closed tab does not haunt a record for the rest of the day.
     */
    protected const TTL_MINUTES = 10;

    /**
     * Record this user as here now, and answer who else already was.
     *
     * Reading and writing happen in one call because that is the one moment
     * presence is ever needed: opening the screen. There is no separate
     * "who is here" query anywhere else, so there is nothing for the two to
     * disagree about.
     *
     * @return Collection<int, User>
     */
    public static function touch(Model $record, User $user): Collection
    {
        $key = self::key($record);
        $cutoff = now()->subMinutes(self::TTL_MINUTES)->timestamp;

        $present = collect(self::entries($key))
            ->filter(fn (int $seenAt) => $seenAt >= $cutoff);

        // Answered before this visit is recorded: nobody is ever told they
        // are keeping themselves company.
        $others = $present->keys()->reject(fn (int $id) => $id === $user->getKey());

        $present[$user->getKey()] = now()->timestamp;

        Cache::put($key, $present->all(), now()->addMinutes(self::TTL_MINUTES));

        return $others->isEmpty()
            ? collect()
            : User::query()->whereKey($others)->get();
    }

    protected static function key(Model $record): string
    {
        return 'presence:'.$record->getMorphClass().':'.$record->getKey();
    }

    /**
     * @return array<int, int>
     */
    protected static function entries(string $key): array
    {
        return (array) Cache::get($key, []);
    }
}