using System.IO.Compression;
using System.Globalization;
using WebDrop.Storage;
using WebDrop.Sync;

namespace WebDrop.Api;

/// <summary>
/// 每天把数据库快照(聊天、头像、账号)压缩后上传到外部存储,只在本地留一个临时文件。
/// 外部存储里按日期留 RetainDays 份:用户删掉的聊天,最多再在备份里留这么久。
/// </summary>
public sealed class BackupWorker(WebDropOptions options, SqliteChannelStore store, ILogger<BackupWorker> logger) : BackgroundService
{
    private readonly HttpClient _http = new() { Timeout = TimeSpan.FromMinutes(30) };
    private const string Prefix = "webdrop-";

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        var backup = options.Backup;
        if (!backup.Enabled || !backup.S3.Configured) return;
        while (!stoppingToken.IsCancellationRequested)
        {
            try { await Task.Delay(DailySchedule.Next(DateTime.Now, backup.TimeOfDay) - DateTime.Now, stoppingToken).ConfigureAwait(false); } catch (OperationCanceledException) { break; }
            try { await RunOnceAsync(DateTime.Now, stoppingToken).ConfigureAwait(false); }
            catch (OperationCanceledException) when (stoppingToken.IsCancellationRequested) { break; }
            catch (Exception e) { logger.LogWarning("数据库备份失败:{Type}", e.GetType().Name); }
        }
    }

    public async Task<(string Name, int Purged)> RunOnceAsync(DateTime now, CancellationToken ct)
    {
        var backup = options.Backup;
        var s3 = new S3Client(_http, backup.S3);
        string tmp = Path.Combine(options.DataDir, "v2", "backup-tmp");
        Directory.CreateDirectory(tmp);
        string name = $"{Prefix}{now:yyyyMMdd-HHmm}.db.gz";
        string db = Path.Combine(tmp, $"snapshot-{Guid.NewGuid():N}.db"), gz = db + ".gz";
        try
        {
            store.Snapshot(db);
            await using (var source = File.OpenRead(db))
            await using (var target = File.Create(gz))
            await using (var zip = new GZipStream(target, CompressionLevel.SmallestSize))
                await source.CopyToAsync(zip, ct).ConfigureAwait(false);
            await using (var upload = File.OpenRead(gz))
                await s3.PutAsync($"chat/{name}", upload, ct).ConfigureAwait(false);
        }
        finally
        {
            foreach (var path in new[] { db, gz }) try { File.Delete(path); } catch (IOException) { }
        }

        // 头像是按内容哈希命名的磁盘文件(不在数据库里):内容不会变,已经上传过的跳过
        foreach (var kind in new[] { "space", "account" })
        {
            string directory = Path.Combine(options.DataDir, "v2", "avatars", kind);
            if (!Directory.Exists(directory)) continue;
            var uploaded = (await s3.ListAsync($"chat/avatars/{kind}", ct).ConfigureAwait(false)).ToHashSet();
            foreach (var file in Directory.EnumerateFiles(directory))
            {
                if (file.EndsWith(".tmp", StringComparison.Ordinal) || uploaded.Contains(Path.GetFileName(file))) continue;
                await using var content = File.OpenRead(file);
                await s3.PutAsync($"chat/avatars/{kind}/{Path.GetFileName(file)}", content, ct).ConfigureAwait(false);
            }
        }

        // 保留期:按文件名里的日期清理更早的
        int purged = 0;
        var cutoff = now.Date.AddDays(-Math.Max(0, backup.RetainDays));
        foreach (var existing in await s3.ListAsync("chat", ct).ConfigureAwait(false))
        {
            if (!existing.StartsWith(Prefix, StringComparison.Ordinal) || existing.Length < Prefix.Length + 8) continue;
            if (!DateTime.TryParseExact(existing.AsSpan(Prefix.Length, 8), "yyyyMMdd", CultureInfo.InvariantCulture, DateTimeStyles.None, out var date) || date >= cutoff) continue;
            if (await s3.DeleteAsync($"chat/{existing}", ct).ConfigureAwait(false)) purged++;
        }
        if (purged > 0) logger.LogInformation("清理了 {Count} 份过期的数据库备份", purged);
        return (name, purged);
    }
}