// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.

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

namespace IISIntegration.FunctionalTests
{
    internal static class HandshakeHelpers
    {
        public static IEnumerable<KeyValuePair<string, string>> GenerateResponseHeaders(string key)
        {
            yield return new KeyValuePair<string, string>(Constants.Headers.Connection, Constants.Headers.Upgrade);
            yield return new KeyValuePair<string, string>(Constants.Headers.Upgrade, Constants.Headers.UpgradeWebSocket);
            yield return new KeyValuePair<string, string>(Constants.Headers.SecWebSocketAccept, CreateResponseKey(key));
        }

        public static string CreateResponseKey(string requestKey)
        {
            // "The value of this header field is constructed by concatenating /key/, defined above in step 4
            // in Section 4.2.2, with the string "258EAFA5- E914-47DA-95CA-C5AB0DC85B11", taking the SHA-1 hash of
            // this concatenated value to obtain a 20-byte value and base64-encoding"
            // https://tools.ietf.org/html/rfc6455#section-4.2.2

            if (requestKey == null)
            {
                throw new ArgumentNullException(nameof(requestKey));
            }

            using (var algorithm = SHA1.Create())
            {
                string merged = requestKey + "258EAFA5-E914-47DA-95CA-C5AB0DC85B11";
                byte[] mergedBytes = Encoding.UTF8.GetBytes(merged);
                byte[] hashedBytes = algorithm.ComputeHash(mergedBytes);
                return Convert.ToBase64String(hashedBytes);
            }
        }
    }
}