using System;

public class Program

{

    public static void Main()

    {

        var state = TaskState.Planned;

        Console.WriteLine(state.ToApiState());

        state = TaskState.Active;

        Console.WriteLine(state.ToApiState());

        state = TaskState.Paused;

        Console.WriteLine(state.ToApiState());

        state = TaskState.Review;

        Console.WriteLine(state.ToApiState());

        state = TaskState.Done;

        Console.WriteLine(state.ToApiState());

    }   

}

​

public enum TaskState

{

    Planned,

    Active,

    Paused,

    Review,

    Done

}

​

public static class TaskStateExtension

{

    public static string ToApiState(this TaskState state)

    {

        var stateString = state.ToString().ToLowerInvariant();

        return stateString;

    }

}

​