using System;
using System.Collections.Generic;
using System.Security.Cryptography;
using System.Text;
using System.Text.RegularExpressions;
using System.Web;

namespace Landmarks_Import
{

    public struct GoogleSignedUrl
    {

        public static string Sign(string url, string keyString)
        {
            ASCIIEncoding encoding = new ASCIIEncoding();

            // converting key to bytes will throw an exception, need to replace '-' and '_' characters first.
            string usablePrivateKey = keyString.Replace("-", "+").Replace("_", "/");
            byte[] privateKeyBytes = Convert.FromBase64String(usablePrivateKey);

            Uri uri = new Uri(url);
            byte[] encodedPathAndQueryBytes = encoding.GetBytes(uri.LocalPath + uri.Query);

            // compute the hash
            HMACSHA1 algorithm = new HMACSHA1(privateKeyBytes);
            byte[] hash = algorithm.ComputeHash(encodedPathAndQueryBytes);

            // convert the bytes to string and make url-safe by replacing '+' and '/' characters
            string signature = Convert.ToBase64String(hash).Replace("+", "-").Replace("/", "_");

            // Add the signature to the existing URI.
            return uri.Scheme + "://" + uri.Host + uri.LocalPath + uri.Query + "&signature=" + signature;
        }
    }
}