<?php

declare(strict_types=1);

namespace App\Services\Traffic;

use Illuminate\Support\Facades\Redis;

final class PresenceIndexPruner
{
    private const SREM_IF_EXPIRED = <<<'LUA'
if redis.call('EXISTS', KEYS[1]) == 0 then
  return redis.call('SREM', KEYS[2], ARGV[1])
end
return 0
LUA;

    /**
     * @return array{scanned:int,stale:int,removed:int,live:int,batches:int,dry_run:bool}
     */
    public function prune(
        int $scanCount,
        int $maxBatches,
        int $maxMembers,
        int $sleepMs,
        bool $dryRun,
        ?int $timeLimitSeconds = null,
    ): array {
        $scanCount = max(10, $scanCount);
        $maxBatches = max(1, $maxBatches);
        $maxMembers = max(1, $maxMembers);
        $started = microtime(true);
        $cursor = 0;
        $scanned = 0;
        $stale = 0;
        $removed = 0;
        $live = 0;
        $batches = 0;

        while ($batches < $maxBatches && $scanned < $maxMembers) {
            if ($timeLimitSeconds !== null && (microtime(true) - $started) >= $timeLimitSeconds) {
                break;
            }

            $result = Redis::sscan(OnlineVisitorRepository::INDEX_KEY, $cursor, ['count' => $scanCount]);
            if (! is_array($result) || count($result) < 2) {
                break;
            }

            $cursor = (int) $result[0];
            $members = $result[1];
            $batches++;

            if ($members === []) {
                if ($cursor === 0) {
                    break;
                }
                continue;
            }

            $recordKeys = [];
            foreach ($members as $member) {
                $member = (string) $member;
                $recordKeys[$member] = OnlineVisitorRepository::KEY_PREFIX.':'.$member;
            }

            $exists = Redis::pipeline(function ($pipe) use ($recordKeys): void {
                foreach ($recordKeys as $recordKey) {
                    $pipe->exists($recordKey);
                }
            });
            if (! is_array($exists)) {
                $exists = [];
            }

            $i = 0;
            foreach ($recordKeys as $member => $recordKey) {
                $scanned++;
                $isLive = (int) ($exists[$i] ?? 0) === 1;
                $i++;
                if ($isLive) {
                    $live++;
                    continue;
                }
                $stale++;
                if ($dryRun) {
                    continue;
                }
                $removed += (int) Redis::eval(
                    self::SREM_IF_EXPIRED,
                    2,
                    $recordKey,
                    OnlineVisitorRepository::INDEX_KEY,
                    $member,
                );
            }

            if ($sleepMs > 0) {
                usleep($sleepMs * 1000);
            }

            if ($cursor === 0) {
                break;
            }
        }

        return [
            'scanned' => $scanned,
            'stale' => $stale,
            'removed' => $removed,
            'live' => $live,
            'batches' => $batches,
            'dry_run' => $dryRun,
        ];
    }
}