using System;

using System.Net;

public class Program

{

    static Uri _baseUri = new Uri("https://fcm.googleapis.com/v1/projects/kobo-dev/");

    public static void Main()

    {

        Console.WriteLine(CombineWithBaseUri("messages:send").AbsoluteUri);

        Console.WriteLine(CombineWithBaseUri("/messages:send").AbsoluteUri);

        Console.WriteLine(CombineWithBaseUri(WebUtility.UrlEncode("messages:send")).AbsoluteUri);

        //var testUri = new Uri("messages:send", UriKind.Relative); // Throws exception "A relative URI cannot be created because the 'uriString' parameter represents an absolute URI."

    }

    public static Uri CombineWithBaseUri(string path)

    {

        var uri = new Uri(path, UriKind.RelativeOrAbsolute); // This is what the framework does when you pass in a string to HttpClient.PostAsync("").

        return CombineWithBaseUri(uri);

    }   

    // This is what the framework does: https://github.com/dotnet/corefx/blob/master/src/System.Net.Http/src/System/Net/Http/HttpClient.cs#L658-L668

    public static Uri CombineWithBaseUri(Uri path)

    {

        if (path.IsAbsoluteUri)

            return path;

        return new Uri(_baseUri, path);

    }   

}