using System;
using System.Collections.Generic;
using System.Linq;
using KitsuneCafe.Sys;
using R3;
using UnityEngine;
using UnityEngine.UIElements;

namespace KitsuneCafe.Extension
{
  public static class R3Extensions
  {
    public static Observable<TResult> Compose<TSource, TResult>(this Observable<TSource> source, Func<Observable<TSource>, Observable<TResult>> transform) =>
      transform(source);

    private struct SmoothDampState
    {
      public float Value;
      public float Velocity;

      public SmoothDampState(float initialValue, float initialVelocity)
      {
        Value = initialValue;
        Velocity = initialVelocity;
      }

      public SmoothDampState(float initialValue) : this(initialValue, 0) { }
    }

    public static Observable<float> EveryUpdateDelta(this TimeProvider provider)
    {
      provider ??= UnityTimeProvider.Update;

      return provider.TryGetFrameProvider(out var frameProvider) ?
        Observable.EveryUpdate(frameProvider)
          .Select(_ => provider.GetDeltaTime(Time.deltaTime)) :
        Observable.Empty<float>();
    }

    private static readonly Lazy<IEqualityComparer<float>> floatComparer = new(
      () => FEqualityComparer<float>.Create(KMath.IsApproxEqual)
    );

    public static Observable<float> SmoothDamp(
        this Observable<float> source,
        Func<float> valueGetter,
        float smoothTime,
        float maxSpeed,
        TimeProvider provider) =>
      source
        .DistinctUntilChanged(floatComparer.Value)
        .Select(target => Observable.EveryUpdate(provider.GetFrameProvider())
          .Scan(new SmoothDampState(valueGetter()),
              (state, _) =>
            {
              var currentVelocity = state.Velocity;
              var nextValue = Mathf.SmoothDamp(
                state.Value,
                target,
                ref currentVelocity,
                smoothTime,
                maxSpeed,
                provider.GetDeltaTime()
              );

              return new SmoothDampState(nextValue, currentVelocity);
            })
            .Select(state => state.Value)
            .TakeWhile(val => Mathf.Abs(val - target) > float.Epsilon)
            .Concat(Observable.Return(target)))
          .Switch();

    public static Observable<float> SmoothDamp(
        this Observable<float> source,
        Func<float> valueGetter,
        float smoothTime) =>
      SmoothDamp(source, valueGetter, smoothTime, Mathf.Infinity, UnityTimeProvider.Update);

    public static Observable<float> SmoothDamp(
        this Observable<float> source,
        Func<float> valueGetter,
        float smoothTime,
        float maxSpeed) =>
      SmoothDamp(source, valueGetter, smoothTime, maxSpeed, UnityTimeProvider.Update);

    public static Observable<float> SmoothDamp(
        this Observable<float> source,
        Func<float> valueGetter,
        float smoothTime,
        TimeProvider provider) =>
      SmoothDamp(source, valueGetter, smoothTime, Mathf.Infinity, provider);

    public static TSource MinBy<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector)
        where TKey : IComparable<TKey>
    {
      if (source == null) throw new ArgumentNullException(nameof(source));
      if (keySelector == null) throw new ArgumentNullException(nameof(keySelector));

      using var enumerator = source.GetEnumerator();

      if (!enumerator.MoveNext())
      {
        return default;
      }

      TSource minElement = enumerator.Current;
      TKey minKey = keySelector(minElement);

      while (enumerator.MoveNext())
      {
        TSource currentElement = enumerator.Current;
        TKey currentKey = keySelector(currentElement);

        if (currentKey.CompareTo(minKey) < 0)
        {
          minKey = currentKey;
          minElement = currentElement;
        }
      }
      return minElement;
    }

    public static Observable<TResult> SelectSwitch<T, TResult>(this Observable<T> source, Func<T, Observable<TResult>> selector) =>
      source.Select(selector).Switch();

    public static Observable<T> SwitchIfElse<T>(this Observable<bool> source, Func<Observable<T>> ifTrue, Observable<T> ifFalse) =>
      SwitchIf(ifFalse, source, ifTrue);

    public static Observable<T> SwitchIfElse<T>(this Observable<bool> source, Observable<T> ifTrue, Observable<T> ifFalse) =>
      SwitchIf(ifFalse, source, ifTrue);

    public static Observable<T> SwitchIf<T>(this Observable<T> source, Observable<bool> selectionSource, Observable<T> other) =>
      selectionSource.SelectSwitch(value => value ? other : source);

    public static Observable<T> SwitchIf<T>(this Observable<T> source, Observable<bool> selectionSource, Func<Observable<T>> other) =>
      selectionSource.SelectSwitch(value => value ? other() : source);

    public static Observable<T> WhereEquals<T>(this Observable<T> source, T value) where T : IEquatable<T> =>
      source.Where(value.Equals);

    public static Observable<bool> WhereTrue(this Observable<bool> source) =>
      source.Where(Func.Identity);

    public static Observable<bool> WhereFalse(this Observable<bool> source) =>
      WhereEquals(source, false);

    public static Observable<T> ObserveBool<T>(this T component, Func<T, bool> predicate) where T : MonoBehaviour
    {
      if (predicate(component))
      {
        return Observable.Return(component);
      }

      return Observable.EveryValueChanged(component, predicate)
          .Where(Func.Identity)
          .Take(1)
          .Select(_ => component);
    }

    public static Observable<T> ObserveAwake<T>(this T component) where T : MonoBehaviour =>
      component.ObserveBool(c => c.didAwake);

    public static Observable<T> ObserveStart<T>(this T component) where T : MonoBehaviour =>
      component.ObserveBool(c => c.didStart);

    public static Observable<TResult> SelectOrDefault<TValue, TResult>(this Observable<TValue> source, Func<TValue, TResult> selector) =>
      source.Select(value => EqualityComparer<TValue>.Default.Equals(value, default) ? default : selector(value));

    public static Observable<TResult> ObserveValueChanged<TResult>(this VisualElement ve)
    {
      var subject = new Subject<TResult>();
      void OnNext(ChangeEvent<TResult> evt)
      {
        subject.OnNext(evt.newValue);
      }

      ve.RegisterCallback<ChangeEvent<TResult>>(OnNext);
      return subject.AsObservable();
    }
    private readonly struct TimeProviderInfo
    {
      public readonly FrameProvider FrameProvider;
      public readonly TimeKind TimeKind;

      public TimeProviderInfo(FrameProvider frameProvider, TimeKind timeKind)
      {
        FrameProvider = frameProvider;
        TimeKind = timeKind;
      }
    }

    private static readonly Dictionary<TimeProvider, TimeProviderInfo> timeProviderInfo = new()
        {
            { UnityTimeProvider.Initialization, new (UnityFrameProvider.Initialization, TimeKind.Time) },
            { UnityTimeProvider.EarlyUpdate, new (UnityFrameProvider.EarlyUpdate, TimeKind.Time) },
            { UnityTimeProvider.FixedUpdate, new (UnityFrameProvider.FixedUpdate, TimeKind.Time) },
            { UnityTimeProvider.PreUpdate, new (UnityFrameProvider.PreUpdate, TimeKind.Time) },
            { UnityTimeProvider.Update, new (UnityFrameProvider.Update, TimeKind.Time) },
            { UnityTimeProvider.PreLateUpdate, new (UnityFrameProvider.PreLateUpdate, TimeKind.Time) },
            { UnityTimeProvider.PostLateUpdate, new (UnityFrameProvider.PostLateUpdate, TimeKind.Time) },
            { UnityTimeProvider.TimeUpdate, new (UnityFrameProvider.TimeUpdate, TimeKind.Time) },

            { UnityTimeProvider.InitializationIgnoreTimeScale, new (UnityFrameProvider.Initialization, TimeKind.UnscaledTime) },
            { UnityTimeProvider.EarlyUpdateIgnoreTimeScale, new (UnityFrameProvider.EarlyUpdate, TimeKind.UnscaledTime) },
            { UnityTimeProvider.FixedUpdateIgnoreTimeScale, new (UnityFrameProvider.FixedUpdate, TimeKind.UnscaledTime) },
            { UnityTimeProvider.PreUpdateIgnoreTimeScale, new (UnityFrameProvider.PreUpdate, TimeKind.UnscaledTime) },
            { UnityTimeProvider.UpdateIgnoreTimeScale, new (UnityFrameProvider.Update, TimeKind.UnscaledTime) },
            { UnityTimeProvider.PreLateUpdateIgnoreTimeScale, new (UnityFrameProvider.PreLateUpdate, TimeKind.UnscaledTime) },
            { UnityTimeProvider.PostLateUpdateIgnoreTimeScale, new (UnityFrameProvider.PostLateUpdate, TimeKind.UnscaledTime) },
            { UnityTimeProvider.TimeUpdateIgnoreTimeScale, new (UnityFrameProvider.TimeUpdate, TimeKind.UnscaledTime) },

            { UnityTimeProvider.InitializationRealtime, new (UnityFrameProvider.Initialization, TimeKind.Realtime) },
            { UnityTimeProvider.EarlyUpdateRealtime, new (UnityFrameProvider.EarlyUpdate, TimeKind.Realtime) },
            { UnityTimeProvider.FixedUpdateRealtime, new (UnityFrameProvider.FixedUpdate, TimeKind.Realtime) },
            { UnityTimeProvider.PreUpdateRealtime, new (UnityFrameProvider.PreUpdate, TimeKind.Realtime) },
            { UnityTimeProvider.UpdateRealtime, new (UnityFrameProvider.Update, TimeKind.Realtime) },
            { UnityTimeProvider.PreLateUpdateRealtime, new (UnityFrameProvider.PreLateUpdate, TimeKind.Realtime) },
            { UnityTimeProvider.PostLateUpdateRealtime, new (UnityFrameProvider.PostLateUpdate, TimeKind.Realtime) },
            { UnityTimeProvider.TimeUpdateRealtime, new (UnityFrameProvider.TimeUpdate, TimeKind.Realtime) }
        };

    public enum PlayerLoopTiming
    {
      Initialization,
      EarlyUpdate,
      FixedUpdate,
      PreUpdate,
      Update,
      PreLateUpdate,
      PostLateUpdate,
      TimeUpdate,
      PostFixedUpdate
    }

    private static readonly Dictionary<FrameProvider, PlayerLoopTiming> frameProviderTiming = new()
        {
            { UnityFrameProvider.Initialization, PlayerLoopTiming.Initialization },
            { UnityFrameProvider.EarlyUpdate, PlayerLoopTiming.EarlyUpdate },
            { UnityFrameProvider.FixedUpdate, PlayerLoopTiming.FixedUpdate },
            { UnityFrameProvider.PreUpdate, PlayerLoopTiming.PreUpdate },
            { UnityFrameProvider.Update, PlayerLoopTiming.Update },
            { UnityFrameProvider.PreLateUpdate, PlayerLoopTiming.PreLateUpdate },
            { UnityFrameProvider.PostLateUpdate, PlayerLoopTiming.PostLateUpdate },
            { UnityFrameProvider.TimeUpdate, PlayerLoopTiming.TimeUpdate },
            { UnityFrameProvider.PostFixedUpdate, PlayerLoopTiming.PostFixedUpdate },

        };


    public static bool TryGetFrameProvider(this TimeProvider provider, out FrameProvider frameProvider)
    {
      if (timeProviderInfo.TryGetValue(provider, out var info))
      {
        frameProvider = info.FrameProvider;
        return true;
      }
      else
      {
        frameProvider = null;
        return false;
      }
    }

    public static FrameProvider GetFrameProvider(this TimeProvider provider) =>
        TryGetFrameProvider(provider, out var frameProvider) ? frameProvider : null;

    public static FrameProvider GetFrameProvider(this PlayerLoopTiming timing) =>
        timing switch
        {
          PlayerLoopTiming.Initialization => UnityFrameProvider.Initialization,
          PlayerLoopTiming.EarlyUpdate => UnityFrameProvider.EarlyUpdate,
          PlayerLoopTiming.FixedUpdate => UnityFrameProvider.FixedUpdate,
          PlayerLoopTiming.PreUpdate => UnityFrameProvider.PreUpdate,
          PlayerLoopTiming.Update => UnityFrameProvider.Update,
          PlayerLoopTiming.PreLateUpdate => UnityFrameProvider.PreLateUpdate,
          PlayerLoopTiming.PostLateUpdate => UnityFrameProvider.PostLateUpdate,
          PlayerLoopTiming.TimeUpdate => UnityFrameProvider.TimeUpdate,
          PlayerLoopTiming.PostFixedUpdate => UnityFrameProvider.PostFixedUpdate,
          _ => throw new ArgumentOutOfRangeException(timing.ToString()),
        };

    public static bool TryGetDeltaTime(this TimeProvider provider, out float deltaTime)
    {
      if (
          timeProviderInfo.TryGetValue(provider, out var info)
          && info.FrameProvider.TryGetFrameTiming(out var timing)
          && (info.TimeKind != TimeKind.Realtime)
      )
      {
        deltaTime = (timing, info.TimeKind) switch
        {
          (PlayerLoopTiming.FixedUpdate, TimeKind.Time) => Time.fixedDeltaTime,
          (PlayerLoopTiming.FixedUpdate, TimeKind.UnscaledTime) => Time.fixedUnscaledDeltaTime,
          (_, TimeKind.Time) => Time.deltaTime,
          (_, TimeKind.UnscaledTime) => Time.unscaledDeltaTime,
          (_, _) => default
        };

        return true;
      }
      else
      {
        deltaTime = default;
        return false;
      }
    }

    public static float GetDeltaTime(this TimeProvider provider, float defaultValue = default) =>
      TryGetDeltaTime(provider, out var deltaTime) ? deltaTime : defaultValue;

    public static bool TryGetFrameTiming(this FrameProvider provider, out PlayerLoopTiming timing) =>
      frameProviderTiming.TryGetValue(provider, out timing);

    public static PlayerLoopTiming? GetFrameTiming(this UnityFrameProvider provider) =>
      provider.TryGetFrameTiming(out var timing) ? timing : null;

    public static TimeProvider GetTimeProvider(PlayerLoopTiming timing, TimeKind kind) =>
      (timing, kind) switch
      {
        (PlayerLoopTiming.Initialization, TimeKind.Time) => UnityTimeProvider.Initialization,
        (PlayerLoopTiming.Initialization, TimeKind.UnscaledTime) => UnityTimeProvider.InitializationIgnoreTimeScale,
        (PlayerLoopTiming.Initialization, TimeKind.Realtime) => UnityTimeProvider.InitializationRealtime,

        (PlayerLoopTiming.EarlyUpdate, TimeKind.Time) => UnityTimeProvider.EarlyUpdate,
        (PlayerLoopTiming.EarlyUpdate, TimeKind.UnscaledTime) => UnityTimeProvider.EarlyUpdate,
        (PlayerLoopTiming.EarlyUpdate, TimeKind.Realtime) => UnityTimeProvider.EarlyUpdate,

        (PlayerLoopTiming.FixedUpdate, TimeKind.Time) => UnityTimeProvider.FixedUpdate,
        (PlayerLoopTiming.FixedUpdate, TimeKind.UnscaledTime) => UnityTimeProvider.FixedUpdate,
        (PlayerLoopTiming.FixedUpdate, TimeKind.Realtime) => UnityTimeProvider.FixedUpdate,

        (PlayerLoopTiming.PreUpdate, TimeKind.Time) => UnityTimeProvider.PreUpdate,
        (PlayerLoopTiming.PreUpdate, TimeKind.UnscaledTime) => UnityTimeProvider.PreUpdate,
        (PlayerLoopTiming.PreUpdate, TimeKind.Realtime) => UnityTimeProvider.PreUpdate,

        (PlayerLoopTiming.Update, TimeKind.Time) => UnityTimeProvider.Update,
        (PlayerLoopTiming.Update, TimeKind.UnscaledTime) => UnityTimeProvider.Update,
        (PlayerLoopTiming.Update, TimeKind.Realtime) => UnityTimeProvider.Update,

        (PlayerLoopTiming.PreLateUpdate, TimeKind.Time) => UnityTimeProvider.PreLateUpdate,
        (PlayerLoopTiming.PreLateUpdate, TimeKind.UnscaledTime) => UnityTimeProvider.PreLateUpdate,
        (PlayerLoopTiming.PreLateUpdate, TimeKind.Realtime) => UnityTimeProvider.PreLateUpdate,

        (PlayerLoopTiming.PostLateUpdate, TimeKind.Time) => UnityTimeProvider.PostLateUpdate,
        (PlayerLoopTiming.PostLateUpdate, TimeKind.UnscaledTime) => UnityTimeProvider.PostLateUpdate,
        (PlayerLoopTiming.PostLateUpdate, TimeKind.Realtime) => UnityTimeProvider.PostLateUpdate,

        (PlayerLoopTiming.TimeUpdate, TimeKind.Time) => UnityTimeProvider.TimeUpdate,
        (PlayerLoopTiming.TimeUpdate, TimeKind.UnscaledTime) => UnityTimeProvider.TimeUpdate,
        (PlayerLoopTiming.TimeUpdate, TimeKind.Realtime) => UnityTimeProvider.TimeUpdate,

        (var t, var k) => throw new ArgumentException("({t}, {k}) are not valid values.")
      };
  }
}