using WebDrop.FileProtocol;
using WebDrop.Sync;

namespace WebDrop.FileApi;

public sealed record SyncSummary(int Uploaded, long UploadedBytes, int Failed, int Purged);

/// <summary>
/// 每天定时把新增的文件帧同步到外部存储(WebDAV,如 OpenList);删除了的内容在外部存储里再留 RetainDays 天才清理。
/// 帧的文件名里就是 频道/条目/序号,一帧一个远端文件,重复上传同样内容是幂等的,中途失败下次接着传。
/// </summary>
public sealed class SyncWorker(FileApiOptions options, FrameStore store, ILogger<SyncWorker> logger) : BackgroundService
{
    private readonly HttpClient _http = new() { Timeout = TimeSpan.FromMinutes(30) };

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        var backup = options.Backup;
        if (!backup.Enabled || !backup.WebDav.Configured) return;
        while (!stoppingToken.IsCancellationRequested)
        {
            var wait = DailySchedule.Next(DateTime.Now, backup.TimeOfDay) - DateTime.Now;
            try { await Task.Delay(wait, stoppingToken).ConfigureAwait(false); } catch (OperationCanceledException) { break; }
            try { await RunOnceAsync(stoppingToken).ConfigureAwait(false); }
            catch (OperationCanceledException) when (stoppingToken.IsCancellationRequested) { break; }
            catch (Exception e) { logger.LogWarning("文件同步失败:{Type}", e.GetType().Name); }
        }
    }

    public async Task<SyncSummary> RunOnceAsync(CancellationToken ct)
    {
        var backup = options.Backup;
        var dav = new WebDavClient(_http, backup.WebDav);
        var throttle = new Throttle(backup.MaxBytesPerSecond);
        int uploaded = 0, failed = 0, purged = 0; long bytes = 0;

        foreach (var (key, path) in store.Unsynced())
        {
            ct.ThrowIfCancellationRequested();
            var started = DateTime.UtcNow;
            try
            {
                await using var file = File.OpenRead(path);
                long length = file.Length; // 上传结束后流已经被释放
                await dav.PutAsync($"files/{key}", file, ct).ConfigureAwait(false);
                store.MarkSynced(key);
                uploaded++; bytes += length;
                await throttle.AfterAsync(length, DateTime.UtcNow - started, ct).ConfigureAwait(false);
            }
            catch (Exception e) when (e is HttpRequestException or IOException)
            {
                // 外部存储连不上或这一帧读不了(正好被删):记一笔,连续失败几次就等下一次再来
                if (++failed >= 5) break;
            }
        }

        // 保留期已过的删除记录:从外部存储清掉
        var expired = store.ExpiredTombstones(TimeSpan.FromDays(Math.Max(0, backup.RetainDays)));
        var cleaned = new List<string>();
        foreach (var prefix in expired)
        {
            try { await dav.DeleteAsync($"files/{prefix}", ct).ConfigureAwait(false); cleaned.Add(prefix); purged++; }
            catch (HttpRequestException) { break; }
        }
        store.RemoveTombstones(cleaned);

        if (uploaded + purged + failed > 0) logger.LogInformation("文件同步:上传 {Uploaded} 帧({Bytes} 字节),失败 {Failed},清理 {Purged}", uploaded, bytes, failed, purged);
        return new SyncSummary(uploaded, bytes, failed, purged);
    }
}