using Fleet.Core;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;
using Monitor.Protocol;

namespace Monitor.Backend.Application;

/// <summary>重启后热层为空：从原始块回填最近 1 小时（低优先级、逐块让出）。完成之前查询规划器不会选用热层。</summary>
public sealed partial class HotLayerBackfill : BackgroundService
{
    private readonly HotLayer _hot;
    private readonly IRawStore _raw;
    private readonly TimeProvider _time;
    private readonly ILogger<HotLayerBackfill> _logger;

    public HotLayerBackfill(HotLayer hot, IRawStore raw, TimeProvider time, ILogger<HotLayerBackfill> logger)
    {
        _hot = hot;
        _raw = raw;
        _time = time;
        _logger = logger;
    }

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        try
        {
            await RunAsync(stoppingToken);
        }
        catch (OperationCanceledException) when (stoppingToken.IsCancellationRequested)
        {
            // 正常停止
        }
        catch (Exception ex)
        {
            // 回填失败不应该让热层永远不可用：标记就绪，缺的部分会通过降级到 10s 层之外的查询体现
            LogFailed(ex);
            _hot.MarkReady();
        }
    }

    /// <summary>回填（也供测试直接调用）。</summary>
    public async Task RunAsync(CancellationToken ct)
    {
        long now = _time.GetUtcNow().ToUnixTimeMilliseconds();
        long from = now - (long)HotLayer.Retention.TotalMilliseconds - 600_000;
        foreach ((NodeId agent, string series) in await _raw.ListSeriesAsync(from, now, ct))
        {
            IReadOnlyList<RawChunkMeta> metas = await _raw.FindAsync(new RawQuery(agent, series, FromMs: from, ToMs: now, Limit: 2000), ct);
            foreach (RawChunkMeta meta in metas.Where(m => m.TestId is null))
            {
                byte[]? bytes = await _raw.ReadAsync(meta, ct);
                if (bytes is not null && RawChunkCodec.Decode(bytes).TryGet(out RawChunk? chunk, out _))
                {
                    _hot.Merge(agent, series, chunk);
                }

                await Task.Yield();
            }
        }

        _hot.MarkReady();
    }

    [LoggerMessage(Level = LogLevel.Error, Message = "hot layer backfill failed")]
    private partial void LogFailed(Exception exception);
}