StateMachine

using System;
using System.Collections.Generic;
using System.Linq;

using UniRx;

namespace AnimalSimulator.Infrastructure
{
    public class StateMachine
    {
        public readonly Subject<IExitableState> OnStateChanged = new Subject<IExitableState>();
        private readonly Dictionary<Type, IExitableState> _states;
        private IExitableState _activeState;

        public StateMachine(IExitableState[] states) =>
            _states = states.ToDictionary(state => state.GetType());

        public void Enter<TState>() where TState : class, IState =>
            ChangeState<TState>().Enter();

        public void Enter<TState, TPayload>(TPayload payload) where TState : class, IPayloadedState<TPayload> =>
            ChangeState<TState>().Enter(payload);

        private TState ChangeState<TState>() where TState : class, IExitableState
        {
            _activeState?.Exit();

            var state = GetState<TState>();
            _activeState = state;

            OnStateChanged.OnNext(_activeState);

            return state;
        }

        private TState GetState<TState>() where TState : class, IExitableState =>
            _states[typeof(TState)] as TState;
    }
}