<?php
/**
 * Minimal S3 client for Hetzner Object Storage (or any S3-compatible store).
 * Implements AWS Signature v4 in plain PHP — no SDK, no Composer.
 *
 * - Presigned GET  → visitors load gallery images directly from S3
 * - Presigned PUT  → the admin browser uploads directly to S3
 * - Signed DELETE  → server-side cleanup when images/galleries are removed
 *
 * Uses path-style URLs: https://<endpoint>/<bucket>/<key>
 */

declare(strict_types=1);

/** Percent-encode an object key, keeping the "/" separators. */
function s3_encode_key(string $key): string
{
    return implode('/', array_map('rawurlencode', explode('/', $key)));
}

function s3_host(): string
{
    return parse_url(config('s3.endpoint'), PHP_URL_HOST);
}

/** HMAC-SHA256 chain producing the SigV4 signing key. */
function s3_signing_key(string $date): string
{
    $k = hash_hmac('sha256', $date, 'AWS4' . config('s3.secret_key'), true);
    $k = hash_hmac('sha256', config('s3.region'), $k, true);
    $k = hash_hmac('sha256', 's3', $k, true);
    return hash_hmac('sha256', 'aws4_request', $k, true);
}

/**
 * SigV4 query-string signing core. Separated from s3_presign() so the
 * algorithm can be verified against the official AWS example vectors.
 * Returns the full query string including X-Amz-Signature.
 */
function s3_presign_query(
    string $method,
    string $host,
    string $canonicalUri,
    string $accessKey,
    string $secretKey,
    string $region,
    int $ttl,
    string $amzDate
): string {
    $date = substr($amzDate, 0, 8);
    $scope = $date . '/' . $region . '/s3/aws4_request';

    $query = [
        'X-Amz-Algorithm'     => 'AWS4-HMAC-SHA256',
        'X-Amz-Credential'    => $accessKey . '/' . $scope,
        'X-Amz-Date'          => $amzDate,
        'X-Amz-Expires'       => (string)$ttl,
        'X-Amz-SignedHeaders' => 'host',
    ];
    ksort($query);
    $canonicalQuery = implode('&', array_map(
        fn($k, $v) => rawurlencode($k) . '=' . rawurlencode($v),
        array_keys($query),
        $query
    ));

    $canonicalRequest = implode("\n", [
        strtoupper($method),
        $canonicalUri,
        $canonicalQuery,
        'host:' . $host,
        '',
        'host',
        'UNSIGNED-PAYLOAD',
    ]);

    $stringToSign = implode("\n", [
        'AWS4-HMAC-SHA256',
        $amzDate,
        $scope,
        hash('sha256', $canonicalRequest),
    ]);

    $k = hash_hmac('sha256', $date, 'AWS4' . $secretKey, true);
    $k = hash_hmac('sha256', $region, $k, true);
    $k = hash_hmac('sha256', 's3', $k, true);
    $k = hash_hmac('sha256', 'aws4_request', $k, true);
    $signature = hash_hmac('sha256', $stringToSign, $k);

    return $canonicalQuery . '&X-Amz-Signature=' . $signature;
}

/**
 * Build a presigned URL for GET or PUT on an object key.
 * Only the Host header is signed, so the browser is free to set its own
 * Content-Type on PUT.
 */
function s3_presign(string $method, string $key, ?int $ttl = null): string
{
    $ttl ??= (int)config('s3.url_ttl', 3600);
    $canonicalUri = '/' . rawurlencode(config('s3.bucket')) . '/' . s3_encode_key($key);
    $query = s3_presign_query(
        $method,
        s3_host(),
        $canonicalUri,
        config('s3.access_key'),
        config('s3.secret_key'),
        config('s3.region'),
        $ttl,
        gmdate('Ymd\THis\Z')
    );
    return config('s3.endpoint') . $canonicalUri . '?' . $query;
}

function s3_presign_get(string $key, ?int $ttl = null): string
{
    return s3_presign('GET', $key, $ttl);
}

function s3_presign_put(string $key, int $ttl = 900): string
{
    return s3_presign('PUT', $key, $ttl);
}

/**
 * Server-side signed request (header auth). Used for DELETE.
 * Returns [httpStatus, responseBody].
 */
function s3_request(string $method, string $key): array
{
    $host = s3_host();
    $amzDate = gmdate('Ymd\THis\Z');
    $date = substr($amzDate, 0, 8);
    $scope = $date . '/' . config('s3.region') . '/s3/aws4_request';
    $canonicalUri = '/' . rawurlencode(config('s3.bucket')) . '/' . s3_encode_key($key);
    $payloadHash = hash('sha256', '');

    $canonicalRequest = implode("\n", [
        strtoupper($method),
        $canonicalUri,
        '', // no query string
        'host:' . $host,
        'x-amz-content-sha256:' . $payloadHash,
        'x-amz-date:' . $amzDate,
        '',
        'host;x-amz-content-sha256;x-amz-date',
        $payloadHash,
    ]);

    $stringToSign = implode("\n", [
        'AWS4-HMAC-SHA256',
        $amzDate,
        $scope,
        hash('sha256', $canonicalRequest),
    ]);

    $signature = hash_hmac('sha256', $stringToSign, s3_signing_key($date));
    $authorization = 'AWS4-HMAC-SHA256 Credential=' . config('s3.access_key') . '/' . $scope
        . ', SignedHeaders=host;x-amz-content-sha256;x-amz-date'
        . ', Signature=' . $signature;

    $ch = curl_init(config('s3.endpoint') . $canonicalUri);
    curl_setopt_array($ch, [
        CURLOPT_CUSTOMREQUEST  => strtoupper($method),
        CURLOPT_RETURNTRANSFER => true,
        CURLOPT_TIMEOUT        => 30,
        CURLOPT_HTTPHEADER     => [
            'Authorization: ' . $authorization,
            'x-amz-content-sha256: ' . $payloadHash,
            'x-amz-date: ' . $amzDate,
        ],
    ]);
    $body = curl_exec($ch);
    $status = (int)curl_getinfo($ch, CURLINFO_RESPONSE_CODE);
    curl_close($ch);
    return [$status, (string)$body];
}

/** Delete one object. S3 returns 204 for success and for already-gone keys. */
function s3_delete(string $key): bool
{
    [$status] = s3_request('DELETE', $key);
    return $status === 204 || $status === 200 || $status === 404;
}

/** Delete every S3 object referenced by a gallery (originals + thumbs). */
function s3_delete_gallery_objects(array $gallery): void
{
    foreach ($gallery['images'] ?? [] as $img) {
        if (!empty($img['key'])) {
            s3_delete($img['key']);
        }
        if (!empty($img['thumb'])) {
            s3_delete($img['thumb']);
        }
    }
}