<?php
// TonPing webhook helpers: signature check and duplicate guard. No dependencies.
declare(strict_types=1);

/**
 * Verify one TonPing webhook request.
 *
 * @param string $secret    The device webhook secret (whsec_...).
 * @param string $rawBody   The request body exactly as received (do not re-encode it).
 * @param array  $headers   Request headers, any name case. A value is a string, or an array of
 *                          strings (Laravel/Symfony headers->all(), PSR-7 getHeaders()); the first is used.
 * @param int    $now       Current Unix time in seconds (pass time()).
 * @param int    $tolerance Largest accepted gap between the timestamp and $now, in seconds.
 * @return array|null       The decoded JSON on success, null on any failure.
 */
function tonping_verify(string $secret, string $rawBody, array $headers, int $now, int $tolerance = 300): ?array
{
    $h = [];
    foreach ($headers as $name => $value) {
        if (is_array($value)) {
            $value = reset($value);
        }
        if (is_string($name) && is_string($value)) {
            $h[strtolower($name)] = $value;
        }
    }
    $ts = $h['x-tonping-timestamp'] ?? null;
    $sig = $h['x-tonping-signature'] ?? null;
    if ($ts === null || $sig === null || $secret === '') {
        return null;
    }
    if (!preg_match('/\A[0-9]{1,15}\z/', $ts)) {
        return null;
    }
    if (strncmp($sig, 'v1=', 3) !== 0) {
        return null;
    }
    $given = substr($sig, 3);
    $expected = hash_hmac('sha256', $ts . '.' . $rawBody, $secret);
    if (!hash_equals($expected, $given)) {
        return null;
    }
    if (abs($now - (int) $ts) > $tolerance) {
        return null;
    }
    try {
        $event = json_decode($rawBody, true, 512, JSON_THROW_ON_ERROR);
    } catch (JsonException $e) {
        return null;
    }
    return is_array($event) ? $event : null;
}

function tonping_read_ids($fp): array
{
    $ids = [];
    while (($line = fgets($fp)) !== false) {
        $line = rtrim($line, "\r\n");
        if ($line !== '') {
            $ids[] = $line;
        }
    }
    return $ids;
}

function tonping_check_id(string $eventId): string
{
    $eventId = trim($eventId);
    if ($eventId === '' || strpbrk($eventId, "\r\n") !== false) {
        throw new InvalidArgumentException('bad event id');
    }
    return $eventId;
}

/**
 * Where receive.php keeps the ids it has handled: $TONPING_SEEN_STORE, else a file beside
 * this script. Keep it outside the web root (or deny it in the web server) and writable
 * by the PHP user.
 */
function tonping_store_path(): string
{
    $path = getenv('TONPING_SEEN_STORE');
    return is_string($path) && $path !== '' ? $path : __DIR__ . '/tonping-seen-ids';
}

/** Open the dedupe store and take a lock ($mode LOCK_SH or LOCK_EX); the caller must fclose() it. */
function tonping_open_store(string $storePath, int $mode)
{
    $fp = @fopen($storePath, 'c+');
    if ($fp === false) {
        throw new RuntimeException('cannot open dedupe store');
    }
    if (!flock($fp, $mode)) {
        fclose($fp);
        throw new RuntimeException('cannot lock dedupe store');
    }
    return $fp;
}

/** True if $eventId was recorded by tonping_mark_seen. The store holds one id per line. */
function tonping_is_seen(string $storePath, string $eventId): bool
{
    $eventId = tonping_check_id($eventId);
    $fp = tonping_open_store($storePath, LOCK_SH);
    try {
        return in_array($eventId, tonping_read_ids($fp), true);
    } finally {
        flock($fp, LOCK_UN);
        fclose($fp);
    }
}

/** Record $eventId (no-op if present). Only the last $keep ids are kept. */
function tonping_mark_seen(string $storePath, string $eventId, int $keep = 10000): void
{
    $eventId = tonping_check_id($eventId);
    $fp = tonping_open_store($storePath, LOCK_EX);
    try {
        $ids = tonping_read_ids($fp);
        if (in_array($eventId, $ids, true)) {
            return;
        }
        $ids[] = $eventId;
        if (count($ids) > $keep) {
            $ids = array_slice($ids, -$keep);
            ftruncate($fp, 0);
            rewind($fp);
            fwrite($fp, implode("\n", $ids) . "\n");
        } else {
            fseek($fp, 0, SEEK_END);
            fwrite($fp, $eventId . "\n");
        }
        fflush($fp);
    } finally {
        flock($fp, LOCK_UN);
        fclose($fp);
    }
}

/**
 * Run $handler once per event. Returns the HTTP status to answer:
 * 200 when handled or already recorded, 500 when the handler threw (the id is
 * then NOT recorded, so TonPing's retry runs the handler again).
 * Throws RuntimeException when the dedupe store cannot be opened or locked; answer 500 then.
 */
function tonping_handle_once(string $storePath, array $event, callable $handler): int
{
    $eventId = (string) ($event['event_id'] ?? '');
    if (tonping_is_seen($storePath, $eventId)) {
        return 200;
    }
    try {
        $handler($event);
    } catch (Throwable $e) {
        error_log('tonping handler failed for ' . $eventId . ': ' . get_class($e));
        return 500;
    }
    tonping_mark_seen($storePath, $eventId);
    return 200;
}