using NewLife.Data;

namespace NewLife.Algorithms;

/// <summary>平均值采样算法</summary>
public class AverageSampling : ISampling
{
    /// <summary>对齐模式。每个桶X轴对齐方式</summary>
    public AlignModes AlignMode { get; set; }

    /// <summary>插值填充算法</summary>
    public IInterpolation? Interpolation { get; set; } = new LinearInterpolation();

    /// <summary>降采样处理。保留边界两个点</summary>
    /// <param name="data">原始数据（升序）</param>
    /// <param name="threshold">阈值，采样数</param>
    /// <returns>降采样后的数据</returns>
    public TimePoint[] Down(TimePoint[] data, Int32 threshold)
    {
        //if (data == null || data.Length < 2) return data;
        if (data.Length < 2) return data;
        if (threshold < 2 || threshold >= data.Length) return data;

        var buckets = SamplingHelper.SplitByAverage(data.Length, threshold, true);

        // 每个桶选择一个点作为代表
        var sampled = new TimePoint[buckets.Length];
        for (var i = 0; i < buckets.Length; i++)
        {
            var item = buckets[i];
            var start = item.Start;
            var end = item.End;
            var count = end - start;

            Double sum = 0;
            for (var j = start; j < end; j++) sum += data[j].Value;

            TimePoint point = default;
            point.Value = sum / count;

            // 对齐 X 轴（时间）
            point.Time = AlignMode switch
            {
                AlignModes.Right => data[end - 1].Time,
                AlignModes.Center => data[(Int32)Math.Round((start + end - 1) / 2.0)].Time,
                _ => data[start].Time,
            };
            sampled[i] = point;
        }

        return sampled;
    }

    /// <summary>混合处理，降采样和插值，不保留边界节点</summary>
    /// <param name="data">原始数据（升序）</param>
    /// <param name="size">桶大小。如60/3600/86400</param>
    /// <param name="offset">偏移量。时间不是对齐零点时使用</param>
    /// <returns>采样 + 插值结果</returns>
    public TimePoint[] Process(TimePoint[] data, Int32 size, Int32 offset = 0)
    {
        //if (data == null || data.Length < 2) return data;
        if (data.Length < 2) return data;
        if (size <= 1) return data;
        if (Interpolation == null) throw new ArgumentNullException(nameof(Interpolation));

        var xs = new Int64[data.Length];
        for (var i = 0; i < data.Length; i++) xs[i] = data[i].Time;

        var buckets = SamplingHelper.SplitByFixedSize(xs, size, offset);

        // 每个桶选择一个点作为代表
        var sampled = new TimePoint[buckets.Length];
        var last = 0; // 上一个有效点索引，用于跨缺口插值
        for (var i = 0; i < buckets.Length; i++)
        {
            var item = buckets[i];
            if (item.Start < 0)
            {
                // 缺口：使用 last -> item.End 的两个点做线性插值（外推/插值）
                sampled[i].Time = i * size; // 桶起点对齐
                sampled[i].Value = Interpolation.Process(data, last, item.End, i);
                continue;
            }

            var start = item.Start;
            var end = item.End;
            var count = end - start;

            Double sum = 0;
            for (var j = start; j < end; j++) sum += data[j].Value;
            last = end - 1;

            TimePoint point = default;
            point.Value = sum / count;

            point.Time = AlignMode switch
            {
                AlignModes.Right => (i + 1) * size - 1,
                AlignModes.Center => data[(Int32)Math.Round((i + 0.5) * size)].Time,
                _ => i * size,
            };
            sampled[i] = point;
        }

        return sampled;
    }
}