Monogame-Extended/source/MonoGame.Extended/Tweening/Tween.cs

using System;
using Microsoft.Xna.Framework;

namespace MonoGame.Extended.Tweening
{
    public abstract class Tween<T> : Tween
        where T : struct
    {
        internal Tween(object target, float duration, float delay, TweenMember<T> member, T endValue)
            : base(target, duration, delay)
        {
            Member = member;
            _endValue = endValue;
        }

        public TweenMember<T> Member { get; }
        public override string MemberName => Member.Name;

        protected T _startValue;
        protected T _endValue;

        protected override void Initialize()
        {
            _startValue = Member.Value;
        }

        protected override void Swap()
        {
            _endValue = _startValue;
            Initialize();
        }
    }

    public abstract class Tween
    {
        internal Tween(object target, float duration, float delay)
        {
            Target = target;
            Duration = duration;
            Delay = delay;
            IsAlive = true;

            _remainingDelay = delay;
        }

        public object Target { get; }
        public abstract string MemberName { get; }
        public float Duration { get; }
        public float Delay { get; }
        public bool IsPaused { get; set; }
        public bool IsRepeating => _remainingRepeats != 0;
        public bool IsRepeatingForever => _remainingRepeats < 0;
        public bool IsAutoReverse { get; private set; }
        public bool IsAlive { get; private set; }
        public bool IsComplete { get; private set; }
        public float TimeRemaining => Duration - _elapsedDuration;
        public float Completion => MathHelper.Clamp(_completion, 0, 1);

        private Func<float, float> _easingFunction;
        private bool _isInitialized;
        private float _completion;
        private float _elapsedDuration;
        private float _remainingDelay;
        private float _repeatDelay;
        private int _remainingRepeats;
        private Action<Tween> _onBegin;
        private Action<Tween> _onEnd;

        public Tween Easing(Func<float, float> easingFunction) { _easingFunction = easingFunction; return this; }
        public Tween OnBegin(Action<Tween> action) { _onBegin = action; return this; }
        public Tween OnEnd(Action<Tween> action) { _onEnd = action; return this; }
        public Tween Pause() { IsPaused = true; return this; }
        public Tween Resume() { IsPaused = false; return this; }

        public Tween Repeat(int count, float repeatDelay = 0f)
        {
            _remainingRepeats = count;
            _repeatDelay = repeatDelay;
            return this;
        }

        public Tween RepeatForever(float repeatDelay = 0f)
        {
            _remainingRepeats = -1;
            _repeatDelay = repeatDelay;
            return this;
        }

        public Tween AutoReverse()
        {
            if (_remainingRepeats == 0)
                _remainingRepeats = 1;

            IsAutoReverse = true;
            return this;
        }

        protected abstract void Initialize();
        protected abstract void Interpolate(float n);
        protected abstract void Swap();

        public void Cancel()
        {
            _remainingRepeats = 0;
            IsAlive = false;
        }

        public void CancelAndComplete()
        {
            if (IsAlive)
            {
                _completion = 1;

                Interpolate(1);
                IsComplete = true;
                _onEnd?.Invoke(this);
            }

            Cancel();
        }

        public void Update(float elapsedSeconds)
        {
            if(IsPaused || !IsAlive)
                return;

            if (_remainingDelay > 0)
            {
                _remainingDelay -= elapsedSeconds;

                if (_remainingDelay > 0)
                    return;
            }

            if (!_isInitialized)
            {
                _isInitialized = true;
                Initialize();
                _onBegin?.Invoke(this);
            }

            if (IsComplete)
            {
                IsComplete = false;
                _elapsedDuration = 0;
                _onBegin?.Invoke(this);

                if (IsAutoReverse)
                    Swap();
            }

            _elapsedDuration += elapsedSeconds;

            var n = _completion = _elapsedDuration / Duration;

            if (_easingFunction != null)
                n = _easingFunction(n);

            if (_elapsedDuration >= Duration)
            {
                if (_remainingRepeats != 0)
                {
                    if(_remainingRepeats > 0)
                        _remainingRepeats--;

                    _remainingDelay = _repeatDelay;
                }
                else if (_remainingRepeats == 0)
                {
                    IsAlive = false;
                }

                n = _completion = 1;
                IsComplete = true;
            }

            Interpolate(n);

            if (IsComplete)
                _onEnd?.Invoke(this);
        }

    }
}