using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace AnotherReplayReader.Utils
{
    internal static class AIAnalyzeUI
    {
        public record AIAnalyzeProgressData(AIAnalyze.AIChunk Delta, DateTimeOffset? TimeStamp, bool IsExtra);

        public class EmaSpeed
        {
            const double Tau = 5;

            private DateTimeOffset lastEventTime = DateTimeOffset.UtcNow;
            private DateTimeOffset timeSinceLastSpeedMeasure = DateTimeOffset.UtcNow;
            private int bufferedCharactersSinceLastSpeedMeasure = 0;
            private double emaSpeed = double.NaN;

            public void ProcessEvent(AIAnalyzeProgressData data)
            {
                if (data.IsExtra)
                {
                    return;
                }
                if (data.TimeStamp is { } timestamp)
                {
                    lastEventTime = timestamp;
                }
                bufferedCharactersSinceLastSpeedMeasure += data.Delta.Text.Length;
            }

            public double GetDisplaySpeed(DateTimeOffset now)
            {
                // =========================
                // 2. 计算 instant speed（真实时间）
                // =========================
                double instant = 0;
                double dt = (now - timeSinceLastSpeedMeasure).TotalSeconds;

                if (bufferedCharactersSinceLastSpeedMeasure > 0 && dt > 0.05)
                {
                    instant = bufferedCharactersSinceLastSpeedMeasure / dt;

                    // reset window
                    bufferedCharactersSinceLastSpeedMeasure = 0;
                    timeSinceLastSpeedMeasure = now;
                }

                double alpha = 1 - Math.Exp(-dt / Tau);

                if (double.IsNaN(emaSpeed))
                {
                    emaSpeed = instant;
                }
                else
                {
                    emaSpeed += alpha * (instant - emaSpeed);
                }
                double idle = (now - lastEventTime).TotalSeconds;
                double display = emaSpeed;

                if (idle > 0.5)
                {
                    double decay = Math.Exp(-(idle - 0.5) / Tau);
                    display *= decay;
                }
                
                return display;
            }
        }

        public static Action<AIAnalyze.AIChunk> BuildAIChunkReader(Action<AIAnalyzeProgressData> newContent)
        {
            void OnAIChunk(AIAnalyze.AIChunk c)
            {
                if (c.Type == AIAnalyze.AIChunkType.Json)
                {
                    return;
                }
                newContent(new(Delta: c, TimeStamp: DateTimeOffset.UtcNow, IsExtra: false));
            }

            return OnAIChunk;
        }
    }
}