canto/Assets/Scripts/Entity/Motor.cs

using System;
using System.ComponentModel;
using System.Runtime.CompilerServices;
using System.Threading;
using KitsuneCafe.Extension;
using KitsuneCafe.SOAP;
using R3;
using UnityEngine;

namespace KitsuneCafe.Entities
{
  public class Motor : MonoBehaviour, INotifyPropertyChanged
  {
    [Header("Dependencies")]
    [SerializeField]
    private new Rigidbody rigidbody;

    [Header("Movement")]
    [SerializeField]
    private ReactiveSource<Vector2> direction;

    [SerializeField]
    private float maxSpeed = 25f;
    public float DefaultMaxSpeed => maxSpeed;

    [SerializeField]
    private float accelerationTime = 1f;
    public float AccelerationTime => accelerationTime;

    [SerializeField]
    private AnimationCurve accelerationCurve = AnimationCurve.EaseInOut(0, 0, 1, 1);

    [SerializeField]
    private float decelerationTime = 0.5f;
    public float Decelerationtime => decelerationTime;

    [SerializeField]
    private AnimationCurve decelerationCurve = AnimationCurve.EaseInOut(0, 0, 1, 1);

    [SerializeField]
    private float rotationSpeed = 25f;
    public float RotationSpeed => rotationSpeed;

    [Space]
    [SerializeField]
    private float epsilon = 0.001f;
    private float sqEpsilon;

    private readonly ReactiveProperty<float> currentMaxSpeed = new();
    public float MaxSpeed => currentMaxSpeed.Value;
    public ReactiveProperty<float> MaxSpeedSource => currentMaxSpeed;

    private CancellationTokenSource disableCancellationSource;

    public event PropertyChangedEventHandler PropertyChanged;

    private bool canMove = true;
    public bool CanMove
    {
      get => canMove;
      set
      {
        if (canMove != value)
        {
          canMove = value;
          Notify();
        }
      }
    }

    private void OnValidate()
    {
      if (rigidbody == null)
      {
        rigidbody = GetComponent<Rigidbody>();
      }

      sqEpsilon = epsilon * epsilon;
    }

    private void OnEnable()
    {
      disableCancellationSource = new();
      var d = Disposable.CreateBuilder();

      currentMaxSpeed.Value = maxSpeed;

      var directionSource = direction.AsObservable().Select(v2 => new Vector3(v2.x, 0, v2.y));
      var velocitySource = ObserveVelocity(directionSource, currentMaxSpeed, UnityFrameProvider.FixedUpdate);
      var rotationSource = ObserveRotation(directionSource, UnityFrameProvider.FixedUpdate);
      var canMove = this.ObservePropertyChanged(x => x.CanMove).DefaultIfEmpty(CanMove);

      canMove.WhereFalse()
        .Subscribe(_ => StopMoving())
        .AddTo(ref d);

      canMove
          .SwitchIfElse(velocitySource, Observable.Never<Vector3>())
          .Subscribe(Accelerate)
          .AddTo(ref d);

      canMove
          .SwitchIfElse(rotationSource, Observable.Empty<Quaternion>())
          .Where(rotation => Quaternion.Angle(transform.rotation, rotation) > 0.1f)
          .Subscribe(ApplyRotation)
          .AddTo(ref d);

      d.RegisterTo(disableCancellationSource.Token);
    }

    private void OnDisable()
    {
      rigidbody.linearVelocity = Vector3.zero;
      disableCancellationSource.Cancel();
    }

    private void StopMoving()
    {
      rigidbody.linearVelocity = new Vector3(
        0,
        rigidbody.linearVelocity.y,
        0
      );
    }

    private void Accelerate(Vector3 force)
    {
      rigidbody.AddForce(force, ForceMode.Acceleration);
    }

    private void ApplyRotation(Quaternion rotation)
    {
      transform.rotation = Quaternion.Slerp(transform.rotation, rotation, Time.fixedDeltaTime * rotationSpeed);
    }

    private Observable<Quaternion> ObserveRotation(Observable<Vector3> directionSource, FrameProvider provider)
    {
      var targetRotationStream = directionSource
      .Select(inputDir =>
      {
        if (inputDir.sqrMagnitude > sqEpsilon)
        {
          return Quaternion.LookRotation(inputDir.normalized);
        }
        else
        {
          return transform.rotation;
        }
      })
      .DistinctUntilChanged();

      return Observable.EveryUpdate(provider)
          .WithLatestFrom(targetRotationStream, (_, targetRotation) => targetRotation);
    }

    private Observable<Vector3> ObserveVelocity(Observable<Vector3> directionSource, Observable<float> maxSpeedSource, FrameProvider provider)
    {
      return directionSource
          .DistinctUntilChanged()
          .CombineLatest(maxSpeedSource, (direction, currentMaxSpeed) => (direction, currentMaxSpeed))
          .Select(data =>
          {
            var (direction, maxSpeed) = data;
            var start = rigidbody.linearVelocity;
            var targetMagnitude = direction.sqrMagnitude > sqEpsilon ? maxSpeed : 0f;
            var targetVelocity = direction.normalized * targetMagnitude;

            if (start.SqrDistance(targetVelocity) < sqEpsilon)
            {
              if (targetVelocity.sqrMagnitude < sqEpsilon && start.sqrMagnitude < sqEpsilon)
              {
                return Observable.Return(Vector3.zero);
              }
              else
              {
                return Observable.Return((targetVelocity - start) / Time.fixedDeltaTime);
              }
            }

            float lerpDuration;
            AnimationCurve curve;

            if (targetMagnitude > epsilon)
            {
              var ratio = start.magnitude / maxSpeed;
              lerpDuration = accelerationTime * (1f - ratio);
              lerpDuration = Mathf.Max(lerpDuration, 0.05f);
              curve = accelerationCurve;
            }
            else
            {
              lerpDuration = decelerationTime;
              curve = decelerationCurve;
            }

            return Interpolate(start, targetVelocity, lerpDuration, provider, curve)
                      .Select(targetVelocity =>
                      {
                        var currentVelocity = rigidbody.linearVelocity;
                        return (targetVelocity - currentVelocity) / Time.fixedDeltaTime;
                      })
                      .Where(_ => targetVelocity.sqrMagnitude > sqEpsilon || rigidbody.linearVelocity.sqrMagnitude > sqEpsilon)
                      .Select(v3 => new Vector3(v3.x, 0, v3.z))
                      .DefaultIfEmpty(Vector3.zero);
          })
          .Switch();
    }

    private static Observable<Vector3> Interpolate(Vector3 start, Vector3 target, float duration, FrameProvider provider, AnimationCurve curve)
    {
      return Observable.EveryUpdate(provider)
          .Scan(0f, (elapsedTime, _) => elapsedTime + Time.fixedDeltaTime)
          .Select(elapsedTime =>
          {
            var factor = 0f;
            if (duration > float.Epsilon)
            {
              factor = Mathf.Clamp01(elapsedTime / duration);
            }
            else
            {
              factor = 1f;
            }

            var evaluatedFactor = curve.Evaluate(factor);

            return Vector3.Lerp(start, target, evaluatedFactor);
          });
    }

    public void ChangeMaxSpeed(float value)
    {
      currentMaxSpeed.Value = value;
    }

    public void ResetMaxSpeed()
    {
      currentMaxSpeed.Value = maxSpeed;
    }

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