designPatternGuru/DesignPatternGuru/FiniteStateMachine/Process.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace FiniteStateMachine
{
    internal class Process
    {
        private Dictionary<StateTransition, ProcessState> _transitions;
        
        public ProcessState CurrentState { get; private set; }

        public Process()
        {
            CurrentState = ProcessState.Inactive;

            _transitions = new Dictionary<StateTransition, ProcessState>()
            {
                { new StateTransition(ProcessState.Inactive, Command.Exit), ProcessState.Trminated },
                { new StateTransition(ProcessState.Inactive, Command.Begin), ProcessState.Active },
                { new StateTransition(ProcessState.Active, Command.End), ProcessState.Inactive },
                { new StateTransition(ProcessState.Active, Command.Paused), ProcessState.Paused },
                { new StateTransition(ProcessState.Paused, Command.End), ProcessState.Inactive },
                {  new StateTransition (ProcessState.Paused, Command.Resume), ProcessState.Active },
            };
        }

        public ProcessState GetNext(Command command)
        {
            StateTransition transition = new StateTransition(CurrentState, command);
            ProcessState nextState;
            if (!_transitions.TryGetValue(transition, out nextState))
                throw new Exception($"Invalid transition: {CurrentState} → {nextState}");

            return nextState;
        }

        public ProcessState MoveNext(Command command)
        {
            CurrentState = GetNext(command);
            return CurrentState;
        }
    }
}