<?php
// SPDX-License-Identifier: GPL-3.0-or-later
declare(strict_types=1);

namespace Aiwend\Usage;

use Aiwend\Support\Clock;
use Aiwend\Support\OptionStore;

/**
 * Bounded record of budget exhaustion for administrators (Phase 89). One small non-autoloaded option; no email, no external
 * call, no raw address: a client is remembered only as the first six characters of its (already keyed-hash) bucket token, at
 * most MAX_SEEN of them per kind and day. Refusals are frequent during an attack, so the option is rewritten only when something
 * new is learned (a first refusal, a new client, a new day) or at most once per WRITE_INTERVAL seconds.
 */
final class ExhaustionAlerts
{
    public const OPTION = 'aiwend_budget_alerts';
    public const MAX_SEEN = 100;
    public const WRITE_INTERVAL = 300;
    /** The site alert stays up this long after the last refusal unless an administrator changes the limits. */
    public const SITE_WINDOW = 86400;

    public function __construct(private OptionStore $options, private Clock $clock)
    {
    }

    /** @param string $bucket the bucket that refused the request: 'site' or a client bucket name; anything else is ignored */
    public function note(string $bucket): void
    {
        if ($bucket === 'site') {
            $kind = 'site';
            $who = '';
        } else {
            $kind = ClientBudget::kindOf($bucket);
            if ($kind === null) {
                return;
            }
            $who = substr((string) strstr($bucket, '-'), 1, 6);
        }
        $now = $this->clock->now();
        $day = gmdate('Ymd', $now);
        $state = $this->state();
        $row = $state[$kind] ?? null;
        $fresh = !is_array($row) || ($kind !== 'site' && ($row['day'] ?? '') !== $day);
        if ($fresh) {
            $row = ['day' => $day, 'first' => $now, 'last' => $now, 'seen' => [], 'w' => 0];
        }
        $isNew = $kind !== 'site' && !in_array($who, $row['seen'], true) && count($row['seen']) < self::MAX_SEEN;
        if (!$fresh && !$isNew && $now - (int) $row['w'] < self::WRITE_INTERVAL) {
            return;
        }
        if ($isNew) {
            $row['seen'][] = $who;
        }
        $row['last'] = $now;
        $row['w'] = $now;
        $state[$kind] = $row;
        $this->options->set(self::OPTION, $state);
    }

    /**
     * What an administrator should be told now.
     *
     * @return array<string, array{first:int, last:int, clients:int}> keys: site, client, shared, unknown
     */
    public function current(): array
    {
        $now = $this->clock->now();
        $day = gmdate('Ymd', $now);
        $out = [];
        foreach ($this->state() as $kind => $row) {
            if (!is_array($row) || !in_array($kind, ['site', 'client', 'shared', 'unknown'], true)) {
                continue;
            }
            $live = $kind === 'site' ? $now - (int) ($row['last'] ?? 0) < self::SITE_WINDOW : ($row['day'] ?? '') === $day;
            if ($live) {
                $out[$kind] = ['first' => (int) ($row['first'] ?? 0), 'last' => (int) ($row['last'] ?? 0), 'clients' => count((array) ($row['seen'] ?? []))];
            }
        }
        return $out;
    }

    /** Called when an administrator saves new limits: the site alert is stale from that moment. */
    public function clearSite(): void
    {
        $state = $this->state();
        if (isset($state['site'])) {
            unset($state['site']);
            $this->options->set(self::OPTION, $state);
        }
    }

    /** @return array<string, mixed> */
    private function state(): array
    {
        $state = $this->options->get(self::OPTION, []);
        return is_array($state) ? $state : [];
    }
}