using System;

​

namespace RefactoringGuru.DesignPatterns.State.Conceptual

{

    // The Context defines the interface of interest to clients. It also

    // maintains a reference to an instance of a State subclass, which

    // represents the current state of the Context.

    class Context

    {

        // A reference to the current state of the Context.

        private State _state = null;

​

        public Context(State state)

        {

            this.TransitionTo(state);

        }

​

        // The Context allows changing the State object at runtime.

        public void TransitionTo(State state)

        {

            Console.WriteLine($"Context: Transition to {state.GetType().Name}.");

            this._state = state;

            this._state.SetContext(this);

        }

​

        // The Context delegates part of its behavior to the current State

        // object.

        public void Request1()

        {

            this._state.Handle1();

        }

​

        public void Request2()

        {

            this._state.Handle2();

        }

    }

    // The base State class declares methods that all Concrete State should

    // implement and also provides a backreference to the Context object,

    // associated with the State. This backreference can be used by States to

    // transition the Context to another State.

    abstract class State

    {

        protected Context _context;

​

        public void SetContext(Context context)

        {

            this._context = context;

        }

​

        public abstract void Handle1();

​

        public abstract void Handle2();

    }

​

    // Concrete States implement various behaviors, associated with a state of

    // the Context.

    class ConcreteStateA : State

    {

        public override void Handle1()

        {

            Console.WriteLine("ConcreteStateA handles request1.");

            Console.WriteLine("ConcreteStateA wants to change the state of the context.");

            this._context.TransitionTo(new ConcreteStateB());

        }

​

        public override void Handle2()

        {

            Console.WriteLine("ConcreteStateA handles request2.");

        }

    }

​

    class ConcreteStateB : State

    {

        public override void Handle1()

        {

            Console.Write("ConcreteStateB handles request1.");

        }

​

        public override void Handle2()

        {

            Console.WriteLine("ConcreteStateB handles request2.");

            Console.WriteLine("ConcreteStateB wants to change the state of the context.");

            this._context.TransitionTo(new ConcreteStateA());

        }

    }

​

    class Program

    {

        static void Main(string[] args)

        {

            // The client code.

            var context = new Context(new ConcreteStateA());

            context.Request1();

            context.Request2();

        }

    }

}