using System;
using System.Collections;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Runtime.CompilerServices;
using System.Threading;
using KitsuneCafe.Sys.Attributes;
using R3;
using UnityEngine;
using static KitsuneCafe.Extension.R3Extensions;

namespace KitsuneCafe.Sys
{
  public class Raycaster : MonoBehaviour, INotifyPropertyChanged
  {
    private static readonly Lazy<IComparer<RaycastHit>> hitComparer = new(
      () => FComparer<RaycastHit>.Create((a, b) => a.distance.CompareTo(b.distance))
    );

    [SerializeField]
    private bool everyFrame = true;

    [SerializeField, DrawIf(nameof(everyFrame), true)]
    private PlayerLoopTiming updateTiming = PlayerLoopTiming.FixedUpdate;

    [SerializeField]
    private Vector3 direction = Vector3.forward;
    public Vector3 Direction => DirectionFrom(directionSpace, direction, transform);

    [SerializeField]
    private Space directionSpace = Space.World;

    [SerializeField]
    private float maxDistance = 1f;
    public float MaxDistance => maxDistance;

    [SerializeField]
    private LayerMask layerMask = default;
    public LayerMask LayerMask => LayerMask;

    [SerializeField]
    private QueryTriggerInteraction queryTriggerInteraction = QueryTriggerInteraction.UseGlobal;
    public QueryTriggerInteraction QueryTriggerInteraction => queryTriggerInteraction;

    [SerializeField]
    private int bufferSize = 1;
    public int BufferSize => bufferSize;

    private int hitCount = 0;
    public int HitCount
    {
      get => hitCount;
      private set
      {
        if (hitCount != value)
        {
          var isCollidingChanged = value == 0 || hitCount == 0;

          hitCount = value;
          Notify();

          if (isCollidingChanged)
          {
            Notify(nameof(IsColliding));
          }
        }
      }
    }

    public bool IsColliding => hitCount > 0;

    private RaycastHit[] hits;
    private HashSet<int> ids = new();
    public ReadOnlyMemory<RaycastHit> Collisions => new(hits, 0, hitCount);

    public event PropertyChangedEventHandler PropertyChanged;

    private CancellationTokenSource disableCancellationTokenSource;
    private CancellationToken disableCancellationToken => disableCancellationTokenSource.Token;

    private void Reset()
    {
      layerMask = LayerMask.NameToLayer("Default");
    }

    private void OnEnable()
    {
      disableCancellationTokenSource = new();
      hits = new RaycastHit[bufferSize];

      if (everyFrame)
      {
        var source = bufferSize > 1 ?
          RaycastMany() :
          RaycastSingle();

        source.RegisterTo(disableCancellationToken);
      }
    }

    private IDisposable RaycastMany() =>
        Observable.EveryUpdate(updateTiming.GetFrameProvider())
          .WithLatestFrom(DirectionStreamFrom(directionSpace, direction, transform), (_, dir) => dir)
          .Subscribe(dir => RaycastAll(transform.position, dir));

    private IDisposable RaycastSingle() =>
        Observable.EveryUpdate(updateTiming.GetFrameProvider())
          .WithLatestFrom(DirectionStreamFrom(directionSpace, direction, transform), (_, dir) => dir)
          .Subscribe(dir => hitCount = Raycast(transform.position, dir, out hits[0]) ? 1 : 0);

    public bool TryGetClosestHit(out RaycastHit hit)
    {
      if (hitCount > 0)
      {
        SortRaycastHits();
        hit = bufferSize switch
        {
          > 1 => hits[0],
          _ => default
        };

        return true;
      }

      hit = default;
      return false;
    }

    private void SortRaycastHits()
    {
      Array.Sort(hits, hitComparer.Value);
    }

    private static Observable<Vector3> DirectionStreamFrom(Space space, Vector3 direction, Transform target) =>
      space switch
      {
        Space.World => Observable.Return(direction),
        Space.Self => Observable.EveryUpdate(UnityFrameProvider.FixedUpdate)
          .Select(_ => target.TransformDirection(direction)),
        _ => throw new ArgumentOutOfRangeException(space.ToString()),
      };

    private static Vector3 DirectionFrom(Space space, Vector3 direction, Transform target) =>
      space switch
      {
        Space.World => direction,
        Space.Self => target.TransformDirection(direction),
        _ => throw new ArgumentOutOfRangeException(space.ToString()),
      };

    private void OnDisable()
    {
      disableCancellationTokenSource.Cancel();
    }

    public bool Raycast(out RaycastHit hit) => Raycast(
      DirectionFrom(directionSpace, direction, transform),
      out hit
    );

    public bool Raycast(Vector3 direction, out RaycastHit hit) => Raycast(
      transform.position,
      direction,
      out hit
    );

    private bool Raycast(Vector3 position, Vector3 direction, out RaycastHit hit) =>
      Physics.Raycast(
        position,
        direction,
        out hit,
        maxDistance,
        layerMask,
        queryTriggerInteraction
      );

    public bool RaycastAll(Vector3 direction) =>
      RaycastAll(
        transform.position,
        direction
      );

    private bool RaycastAll(Vector3 position, Vector3 direction)
    {
      HitCount = RaycastAll(position, direction, hits);

      NotifyChanges();

      return hitCount > 0;
    }

    private void NotifyChanges()
    {
      var set = new HashSet<int>();
      var notified = false;
      foreach (var hit in Collisions.Span)
      {
        set.Add(hit.colliderInstanceID);

        if (!notified && !ids.Contains(hit.colliderInstanceID))
        {
          notified = true;
          Notify(nameof(Collisions));
        }
      }

      ids.Clear();
      ids.UnionWith(set);
    }

    private int RaycastAll(Vector3 position, Vector3 direction, RaycastHit[] hits) =>
      Physics.RaycastNonAlloc(
        position,
        direction,
        hits,
        maxDistance,
        layerMask,
        queryTriggerInteraction
      );

    private void Notify([CallerMemberName] string name = default)
    {
      PropertyChanged?.Invoke(this, new(name));
    }

    private void OnDrawGizmos()
    {
      Gizmos.color = IsColliding ? Color.green : Color.yellow;
      Gizmos.DrawRay(
        transform.position,
        DirectionFrom(
          directionSpace,
          direction,
          transform
        ) * maxDistance
      );
    }
  }
}