<?php

declare(strict_types=1);

// Dependency-free client for S3-compatible object storage (AWS Signature V4,
// path-style addressing). Requires the BACKUP_SERVER_S3_* constants defined in
// lib.php / config.php.

function backupS3Config(): array
{
    return [
        "endpoint" => rtrim(trim((string) BACKUP_SERVER_S3_ENDPOINT), "/"),
        "region" => trim((string) BACKUP_SERVER_S3_REGION),
        "bucket" => trim((string) BACKUP_SERVER_S3_BUCKET),
        "prefix" => trim((string) BACKUP_SERVER_S3_PREFIX, "/"),
        "access_key" => trim((string) BACKUP_SERVER_S3_ACCESS_KEY),
        "secret_key" => (string) BACKUP_SERVER_S3_SECRET_KEY,
        "timeout" => max(1, (int) BACKUP_SERVER_S3_TIMEOUT),
        "path_style" => (bool) BACKUP_SERVER_S3_PATH_STYLE,
    ];
}

function backupS3Enabled(): bool
{
    if (BACKUP_SERVER_S3_ENABLED !== true) {
        return false;
    }

    $config = backupS3Config();

    return $config["endpoint"] !== "" &&
        $config["region"] !== "" &&
        $config["bucket"] !== "" &&
        $config["access_key"] !== "" &&
        $config["secret_key"] !== "";
}

function backupS3ObjectKey(string $instance, string $filename): string
{
    $config = backupS3Config();
    $key = $instance . "/" . $filename;

    return $config["prefix"] !== "" ? $config["prefix"] . "/" . $key : $key;
}

function backupS3EmptyPayloadHash(): string
{
    return hash("sha256", "");
}

function backupS3HttpStatusFromHeaders(array $headers): int
{
    $status = 0;
    foreach ($headers as $header) {
        if (preg_match('/^HTTP\/\S+\s+(\d+)/', (string) $header, $matches) === 1) {
            $status = (int) $matches[1];
        }
    }

    return $status;
}

// $legacyHeaders must be the caller's $http_response_header, because PHP only
// populates that variable in the scope where the HTTP call was made.
function backupS3ResponseHeaders($legacyHeaders): array
{
    if (function_exists("http_get_last_response_headers")) {
        $lastHeaders = http_get_last_response_headers();
        return is_array($lastHeaders) ? $lastHeaders : [];
    }

    return is_array($legacyHeaders) ? $legacyHeaders : [];
}

function backupS3SignRequest(string $method, string $key, string $payloadHash, array $extraHeaders = []): array
{
    $config = backupS3Config();

    $scheme = parse_url($config["endpoint"], PHP_URL_SCHEME);
    $endpointHost = parse_url($config["endpoint"], PHP_URL_HOST);
    if (!is_string($scheme) || $scheme === "" || !is_string($endpointHost) || $endpointHost === "") {
        throw new RuntimeException("S3 endpoint is invalid.");
    }

    $encodedKey = str_replace("%2F", "/", rawurlencode($key));
    if ($config["path_style"]) {
        // https://<endpoint-host>/<bucket>/<key>
        $host = $endpointHost;
        $canonicalUri = "/" . rawurlencode($config["bucket"]) . "/" . $encodedKey;
    } else {
        // https://<bucket>.<endpoint-host>/<key> (default for Hetzner)
        $host = $config["bucket"] . "." . $endpointHost;
        $canonicalUri = "/" . $encodedKey;
    }

    $port = parse_url($config["endpoint"], PHP_URL_PORT);
    if (is_int($port)) {
        $host .= ":" . $port;
    }

    $url = $scheme . "://" . $host . $canonicalUri;

    $now = gmdate("Ymd\THis\Z");
    $date = substr($now, 0, 8);

    $headers = array_merge($extraHeaders, [
        "host" => $host,
        "x-amz-content-sha256" => $payloadHash,
        "x-amz-date" => $now,
    ]);
    ksort($headers);

    $canonicalHeaders = "";
    foreach ($headers as $name => $value) {
        $canonicalHeaders .= $name . ":" . $value . "\n";
    }
    $signedHeaders = implode(";", array_keys($headers));

    $canonicalRequest =
        $method . "\n" .
        $canonicalUri .
        "\n\n" .
        $canonicalHeaders .
        "\n" .
        $signedHeaders .
        "\n" .
        $payloadHash;
    $scope = $date . "/" . $config["region"] . "/s3/aws4_request";
    $stringToSign =
        "AWS4-HMAC-SHA256\n" .
        $now .
        "\n" .
        $scope .
        "\n" .
        hash("sha256", $canonicalRequest);
    $kDate = hash_hmac("sha256", $date, "AWS4" . $config["secret_key"], true);
    $kRegion = hash_hmac("sha256", $config["region"], $kDate, true);
    $kService = hash_hmac("sha256", "s3", $kRegion, true);
    $kSigning = hash_hmac("sha256", "aws4_request", $kService, true);
    $signature = hash_hmac("sha256", $stringToSign, $kSigning);
    $authorization =
        "AWS4-HMAC-SHA256 Credential=" .
        $config["access_key"] .
        "/" .
        $scope .
        ", SignedHeaders=" .
        $signedHeaders .
        ", Signature=" .
        $signature;

    $headerString = "";
    foreach ($headers as $name => $value) {
        $headerString .= $name . ": " . $value . "\r\n";
    }
    $headerString .= "Authorization: " . $authorization . "\r\n";

    return [
        "url" => $url,
        "headers" => $headerString,
        "timeout" => $config["timeout"],
    ];
}

// Builds a human-readable suffix for an error message from an S3 response.
// S3-compatible endpoints return an XML body like
// <Error><Code>SignatureDoesNotMatch</Code><Message>...</Message></Error>,
// which pinpoints why a request was rejected.
function backupS3ErrorDetail(int $status, $response): string
{
    $detail = $status > 0 ? " (HTTP " . $status . ")" : "";
    $body = is_string($response) ? trim($response) : "";
    if ($body === "") {
        return $detail . ".";
    }

    $parts = [];
    if (preg_match('#<Code>(.*?)</Code>#s', $body, $matches) === 1) {
        $parts[] = trim($matches[1]);
    }
    if (preg_match('#<Message>(.*?)</Message>#s', $body, $matches) === 1) {
        $parts[] = trim($matches[1]);
    }
    if ($parts === []) {
        $parts[] = substr(preg_replace('/\s+/', " ", $body) ?? "", 0, 300);
    }

    return $detail . ": " . implode(" - ", $parts);
}

// Summarizes the response header chain so a failure can be diagnosed from the
// log: every HTTP status line (reveals redirects), any Location target, and the
// server's request id. $headers is the raw wrapper header array.
function backupS3HeaderDiagnostic(array $headers): string
{
    $statuses = [];
    $location = "";
    $requestId = "";
    foreach ($headers as $header) {
        $header = (string) $header;
        if (preg_match('/^HTTP\/\S+\s+(\d+)/', $header, $matches) === 1) {
            $statuses[] = $matches[1];
        } elseif (preg_match('/^Location:\s*(.+)$/i', $header, $matches) === 1) {
            $location = trim($matches[1]);
        } elseif (preg_match('/^x-amz-request-id:\s*(.+)$/i', $header, $matches) === 1) {
            $requestId = trim($matches[1]);
        }
    }

    $parts = [];
    if ($statuses !== []) {
        $parts[] = "status chain " . implode("->", $statuses);
    }
    if ($location !== "") {
        $parts[] = "redirected to " . $location;
    }
    if ($requestId !== "") {
        $parts[] = "request-id " . $requestId;
    }

    return $parts === [] ? "" : " [" . implode("; ", $parts) . "]";
}

function backupS3PutFile(string $localPath, string $key): void
{
    // The whole file is held in memory for signing; a backup larger than
    // memory_limit fails here, stays local, and is retried later.
    $payload = @file_get_contents($localPath);
    if ($payload === false) {
        throw new RuntimeException("Backup file cannot be read for S3 upload.");
    }

    $request = backupS3SignRequest("PUT", $key, hash("sha256", $payload), [
        "content-type" => "application/zip",
    ]);

    $context = stream_context_create([
        "http" => [
            "method" => "PUT",
            "timeout" => $request["timeout"],
            "ignore_errors" => true,
            // Never chase a redirect: PHP would re-send the body with a
            // signature bound to the original host/path, which the target then
            // rejects. A 3xx must surface so the endpoint config can be fixed.
            "follow_location" => 0,
            "max_redirects" => 1,
            "protocol_version" => 1.1,
            "header" => $request["headers"] . "Content-Length: " . strlen($payload) . "\r\n",
            "content" => $payload,
        ],
    ]);

    $response = @file_get_contents($request["url"], false, $context);
    $headers = backupS3ResponseHeaders($http_response_header ?? null);
    $status = backupS3HttpStatusFromHeaders($headers);

    if ($response === false || $status < 200 || $status >= 300) {
        throw new RuntimeException(
            "S3 upload failed" . backupS3ErrorDetail($status, $response) . backupS3HeaderDiagnostic($headers),
        );
    }
}

function backupS3DeleteObject(string $key): void
{
    $request = backupS3SignRequest("DELETE", $key, backupS3EmptyPayloadHash());

    $context = stream_context_create([
        "http" => [
            "method" => "DELETE",
            "timeout" => $request["timeout"],
            "ignore_errors" => true,
            "follow_location" => 0,
            "max_redirects" => 1,
            "protocol_version" => 1.1,
            "header" => $request["headers"],
        ],
    ]);

    $response = @file_get_contents($request["url"], false, $context);
    $headers = backupS3ResponseHeaders($http_response_header ?? null);
    $status = backupS3HttpStatusFromHeaders($headers);

    // DELETE is idempotent: an already missing object (404) counts as deleted.
    if ($response === false || ($status !== 404 && ($status < 200 || $status >= 300))) {
        throw new RuntimeException(
            "S3 delete failed" . backupS3ErrorDetail($status, $response) . backupS3HeaderDiagnostic($headers),
        );
    }
}

function backupS3SendObjectToOutput(string $key, string $downloadName, int $fallbackSize): void
{
    $request = backupS3SignRequest("GET", $key, backupS3EmptyPayloadHash());

    $context = stream_context_create([
        "http" => [
            "method" => "GET",
            "timeout" => $request["timeout"],
            "ignore_errors" => true,
            "follow_location" => 0,
            "max_redirects" => 1,
            "protocol_version" => 1.1,
            "header" => $request["headers"],
        ],
    ]);

    $handle = @fopen($request["url"], "rb", false, $context);
    if ($handle === false) {
        throw new RuntimeException("S3 download failed (connection error).");
    }

    $meta = stream_get_meta_data($handle);
    $headers = isset($meta["wrapper_data"]) && is_array($meta["wrapper_data"])
        ? $meta["wrapper_data"]
        : [];
    $status = backupS3HttpStatusFromHeaders($headers);
    if ($status < 200 || $status >= 300) {
        $body = stream_get_contents($handle, 2048);
        fclose($handle);
        throw new RuntimeException(
            "S3 download failed" . backupS3ErrorDetail($status, $body) . backupS3HeaderDiagnostic($headers),
        );
    }

    $size = $fallbackSize;
    foreach ($headers as $header) {
        if (preg_match('/^Content-Length:\s*(\d+)/i', (string) $header, $matches) === 1) {
            $size = (int) $matches[1];
        }
    }

    header("Content-Type: application/zip");
    header("Content-Disposition: attachment; filename=\"" . addcslashes($downloadName, "\"\\") . "\"");
    if ($size > 0) {
        header("Content-Length: " . (string) $size);
    }
    header("Cache-Control: private, no-store");
    header("X-Content-Type-Options: nosniff");

    fpassthru($handle);
    fclose($handle);
    exit;
}