using FileShare_Services.Services.FileLibrary;
using Microsoft.Extensions.Options;

namespace FileShare_API.Services
{
    /// <summary>
    /// 文件库定时扫描后台服务，按配置间隔检查是否有需要扫描的文件库目录。
    /// </summary>
    public sealed class FileLibraryScanHostedService(
        IServiceScopeFactory scopeFactory,
        IOptions<FileLibraryScanOptions> options,
        ILogger<FileLibraryScanHostedService> logger)
        : BackgroundService
    {
        /// <summary>后台服务检查到期扫描任务的轮询间隔。</summary>
        private readonly TimeSpan _interval = TimeSpan.FromMinutes(Math.Max(1, options.Value.PollingIntervalMinutes));

        /// <summary>
        /// 启动扫描循环，首次立即执行，之后按配置的轮询间隔重复执行。
        /// </summary>
        /// <param name="stoppingToken">应用关闭时触发的取消令牌。</param>
        protected override async Task ExecuteAsync(CancellationToken stoppingToken)
        {
            logger.LogInformation("文件库定时扫描服务已启动，轮询间隔 {IntervalMinutes} 分钟。", _interval.TotalMinutes);
            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)
        {
            var startedAt = DateTime.UtcNow;
            logger.LogInformation("文件库定时扫描轮询开始。");

            try
            {
                await using var scope = scopeFactory.CreateAsyncScope();
                var scanner = scope.ServiceProvider.GetRequiredService<IFileLibraryService>();
                await scanner.ScanDueRootsAsync(cancellationToken);
                logger.LogInformation(
                    "文件库定时扫描轮询完成，耗时 {ElapsedMilliseconds} ms。",
                    (DateTime.UtcNow - startedAt).TotalMilliseconds);
            }
            catch (OperationCanceledException) when (cancellationToken.IsCancellationRequested)
            {
                logger.LogInformation("文件库定时扫描轮询已取消。");
            }
            catch (Exception ex)
            {
                logger.LogWarning(ex, "文件库定时扫描失败。");
            }
        }
    }
}