<?php

/**
 * Download Attachment API
 *
 * Serves file downloads for ticket attachments
 */

require_once dirname(__DIR__) . '/middleware/RateLimitMiddleware.php';
RateLimitMiddleware::apply('api');

require_once dirname(__DIR__) . '/config/config.php';
require_once dirname(__DIR__) . '/helpers/Database.php';
require_once dirname(__DIR__) . '/models/AttachmentModel.php';
require_once dirname(__DIR__) . '/models/TicketModel.php';

// Check authentication
if (!isset($_SESSION['user']) || !isset($_SESSION['user']['user_id'])) {
    http_response_code(401);
    header('Content-Type: application/json');
    echo json_encode(['success' => false, 'error' => 'Authentication required']);
    exit;
}

// Get attachment ID
$attachmentId = isset($_GET['id']) ? (int)$_GET['id'] : 0;
if ($attachmentId <= 0 || (string)$attachmentId !== (string)($_GET['id'] ?? '')) {
    http_response_code(400);
    header('Content-Type: application/json');
    echo json_encode(['success' => false, 'error' => 'Valid attachment ID is required']);
    exit;
}

try {
    $attachmentModel = new AttachmentModel(Database::getConnection());

    // Get attachment details
    $attachment = $attachmentModel->getAttachment($attachmentId);
    if (!$attachment) {
        http_response_code(404);
        header('Content-Type: application/json');
        echo json_encode(['success' => false, 'error' => 'Attachment not found']);
        exit;
    }

    // Verify the associated ticket exists and user has access
    $conn = Database::getConnection();

    $ticketModel = new TicketModel($conn);
    $ticket = $ticketModel->getTicketById($attachment['ticket_id']);

    if (!$ticket) {
        http_response_code(404);
        header('Content-Type: application/json');
        echo json_encode(['success' => false, 'error' => 'Associated ticket not found']);
        exit;
    }

    // Check if user has access to this ticket based on visibility settings
    if (!$ticketModel->canUserAccessTicket($ticket, $_SESSION['user'])) {
        http_response_code(403);
        header('Content-Type: application/json');
        echo json_encode(['success' => false, 'error' => 'Access denied to this ticket']);
        exit;
    }

    $conn->close();

    // Build file path
    $uploadDir = $GLOBALS['config']['UPLOAD_DIR'] ?? dirname(__DIR__) . '/uploads';
    $filePath = $uploadDir . '/' . $attachment['ticket_id'] . '/' . $attachment['filename'];

    // Security: Verify the resolved path is within the uploads directory (prevent path traversal)
    $realUploadDir = realpath($uploadDir);
    $realFilePath = realpath($filePath);

    if ($realFilePath === false || $realUploadDir === false || strpos($realFilePath, $realUploadDir . DIRECTORY_SEPARATOR) !== 0) {
        http_response_code(403);
        header('Content-Type: application/json');
        echo json_encode(['success' => false, 'error' => 'Access denied']);
        exit;
    }

    // Check if file exists
    if (!file_exists($realFilePath)) {
        http_response_code(404);
        header('Content-Type: application/json');
        echo json_encode(['success' => false, 'error' => 'File not found on server']);
        exit;
    }

    // Use the validated real path
    $filePath = $realFilePath;

    // Determine if we should display inline or force download
    $inline = isset($_GET['inline']) && $_GET['inline'] === '1';
    $inlineTypes = ['image/jpeg', 'image/png', 'image/gif', 'image/webp', 'application/pdf', 'text/plain'];

    // Set headers
    $disposition = ($inline && in_array($attachment['mime_type'], $inlineTypes)) ? 'inline' : 'attachment';

    // Sanitize filename for Content-Disposition
    $safeFilename = preg_replace('/[^\w\s\-\.]/', '_', $attachment['original_filename']);

    $fileSize = filesize($filePath);

    // Parse a single-range "Range: bytes=start-end" request header (RFC 7233).
    // Multi-range requests aren't supported; they fall through to a full 200 response.
    $rangeStart = 0;
    $rangeEnd = $fileSize - 1;
    $isRangeRequest = false;

    if (isset($_SERVER['HTTP_RANGE']) && preg_match('/^bytes=(\d*)-(\d*)$/', trim($_SERVER['HTTP_RANGE']), $m)) {
        if ($m[1] === '' && $m[2] === '') {
            // Malformed ("bytes=-") — ignore and serve the full file.
        } elseif ($m[1] === '') {
            // Suffix range: last N bytes
            $suffixLength = (int)$m[2];
            $rangeStart = max(0, $fileSize - $suffixLength);
            $rangeEnd = $fileSize - 1;
            $isRangeRequest = true;
        } else {
            $rangeStart = (int)$m[1];
            $rangeEnd = ($m[2] === '') ? $fileSize - 1 : min((int)$m[2], $fileSize - 1);
            $isRangeRequest = true;
        }

        if ($isRangeRequest && ($rangeStart > $rangeEnd || $rangeStart >= $fileSize)) {
            http_response_code(416);
            header('Content-Range: bytes */' . $fileSize);
            exit;
        }
    }

    $rangeLength = $rangeEnd - $rangeStart + 1;

    header('Accept-Ranges: bytes');
    header('Content-Type: ' . $attachment['mime_type']);
    header('Content-Disposition: ' . $disposition . '; filename="' . $safeFilename . '"');
    header('Cache-Control: private, max-age=3600');
    header('X-Content-Type-Options: nosniff');

    if ($isRangeRequest) {
        http_response_code(206);
        header('Content-Range: bytes ' . $rangeStart . '-' . $rangeEnd . '/' . $fileSize);
    }
    header('Content-Length: ' . $rangeLength);

    // Prevent PHP from timing out on large files
    set_time_limit(0);

    // Clear output buffer
    if (ob_get_level()) {
        ob_end_clean();
    }

    // Stream file
    $handle = fopen($filePath, 'rb');
    if ($handle === false) {
        http_response_code(500);
        header('Content-Type: application/json');
        echo json_encode(['success' => false, 'error' => 'Failed to open file']);
        exit;
    }

    fseek($handle, $rangeStart);
    $remaining = $rangeLength;
    $chunkSize = 8192;
    while ($remaining > 0 && !feof($handle)) {
        $read = ($remaining < $chunkSize) ? $remaining : $chunkSize;
        $data = fread($handle, $read);
        if ($data === false) {
            break;
        }
        echo $data;
        flush();
        $remaining -= strlen($data);
    }

    fclose($handle);
    exit;
} catch (Exception $e) {
    http_response_code(500);
    header('Content-Type: application/json');
    echo json_encode(['success' => false, 'error' => 'Failed to download attachment']);
    exit;
}