using FileShare_Services.Services.FileLibrary;

namespace FileShare_API.Services
{
    /// <summary>
    /// 文件库定时扫描后台服务，每分钟执行一次扫描，检查是否有需要扫描的文件库目录。
    /// </summary>
    public sealed class FileLibraryScanHostedService(IServiceScopeFactory scopeFactory, ILogger<FileLibraryScanHostedService> logger)
        : BackgroundService
    {
        /// <summary>
        /// 扫描间隔，固定为 1 分钟。
        /// </summary>
        private static readonly TimeSpan Interval = TimeSpan.FromMinutes(1);

        /// <summary>
        /// 启动扫描循环，首次立即执行，之后按 <see cref="Interval"/> 周期重复执行。
        /// </summary>
        /// <param name="stoppingToken">应用关闭时触发的取消令牌。</param>
        protected override async Task ExecuteAsync(CancellationToken stoppingToken)
        {
            await ScanAsync(stoppingToken);

            using var timer = new PeriodicTimer(Interval);
            while (await timer.WaitForNextTickAsync(stoppingToken))
            {
                await ScanAsync(stoppingToken);
            }
        }

        /// <summary>
        /// 创建临时作用域并调用 <see cref="IFileLibraryService.ScanDueRootsAsync"/> 执行一次到期扫描。
        /// </summary>
        /// <param name="cancellationToken">取消令牌。</param>
        private async Task ScanAsync(CancellationToken cancellationToken)
        {
            try
            {
                await using var scope = scopeFactory.CreateAsyncScope();
                var scanner = scope.ServiceProvider.GetRequiredService<IFileLibraryService>();
                await scanner.ScanDueRootsAsync(cancellationToken);
            }
            catch (OperationCanceledException) when (cancellationToken.IsCancellationRequested)
            {
            }
            catch (Exception ex)
            {
                logger.LogWarning(ex, "文件库定时扫描失败。");
            }
        }
    }
}