StateSwitch.cs

public class StateSwitch
{
    private readonly Action enterAction;
    private readonly Action leaveAction;

    private readonly bool leaveOnSuspend;

    private uint counter;

    private bool entered;
    private bool suspended;

    public StateSwitch(Action enterAction, Action leaveAction, bool leaveOnSuspend = false)
    {
        this.enterAction = enterAction;
        this.leaveAction = leaveAction;

        this.leaveOnSuspend = leaveOnSuspend;
    }

    public void Enter()
    {
        if (this.counter++ == 0 && !this.suspended)
        {
            this.DoEnter();
        }
    }

    public void Leave()
    {
        if (this.counter == 0)
        {
            throw new InvalidOperationException("Unable to leave state more times than it was entered.");
        }
        
        if (--this.counter == 0 && !this.suspended)
        {
            this.DoLeave();
        }
    }

    public void Suspend()
    {
        if (this.suspended)
        {
            return;
        }

        if (this.leaveOnSuspend && this.entered)
        {
            this.DoLeave();
        }

        this.suspended = true;
    }

    public void Resume()
    {
        if (!this.suspended)
        {
            return;
        }

        this.suspended = false;

        if (this.counter == 0 && this.entered)
        {
            this.DoLeave();
        }
        else if (this.counter > 0 && !this.entered)
        {
            this.DoEnter();
        }
    }

    private void DoEnter()
    {
        this.entered = true;
        this.enterAction();
    }

    private void DoLeave()
    {
        this.entered = false;
        this.leaveAction();
    }
}