using MoShiro.Protocol;

namespace MoShiro.Backend.Analysis;

/// <summary>
/// 把原始块按时间分桶算成累加器。流式路径（1s 桶）和持久路径（分钟窗口）调用同一份代码，
/// 所以实时值与历史值使用的是同一套口径。
/// </summary>
public sealed class WindowEvaluator
{
    private readonly IReadOnlyList<MetricDef> _metrics;

    public WindowEvaluator(IReadOnlyList<MetricDef> metrics)
    {
        _metrics = metrics;
    }

    public static WindowEvaluator Default { get; } = new(MetricRegistry.All);

    /// <summary>
    /// 评估一个块，结果合并进 <paramref name="buckets"/>（键是桶起点的 UTC 毫秒）。
    /// <paramref name="only"/> 不为空时只计算这些指标（用于回填新增或变更的指标）。
    /// </summary>
    public void Evaluate(RawChunk chunk, long bucketMs, IDictionary<long, MetricSet> buckets, ISet<string>? only = null)
    {
        var view = new ChunkView(chunk);
        foreach (RawStream stream in chunk.Streams)
        {
            foreach (MetricDef metric in _metrics)
            {
                if ((only is not null && !only.Contains(metric.Id)) || !metric.Matches(chunk.Header.Kind, stream.Name))
                {
                    continue;
                }

                metric.Op.Evaluate(view, stream, new BucketSink(metric, bucketMs, buckets));
            }
        }
    }

    private sealed class BucketSink : IObservationSink
    {
        private readonly MetricDef _metric;
        private readonly long _bucketMs;
        private readonly IDictionary<long, MetricSet> _buckets;

        public BucketSink(MetricDef metric, long bucketMs, IDictionary<long, MetricSet> buckets)
        {
            _metric = metric;
            _bucketMs = bucketMs;
            _buckets = buckets;
        }

        public void Emit(long utcMs, double a, double b = 0)
        {
            long start = Math.DivRem(utcMs, _bucketMs, out long rem) * _bucketMs;
            if (rem < 0)
            {
                start -= _bucketMs;
            }

            if (!_buckets.TryGetValue(start, out MetricSet? set))
            {
                set = new MetricSet();
                _buckets[start] = set;
            }

            set.GetOrAdd(_metric.Id, _metric.Kind).Add(a, b);
        }
    }
}