osu/osu.Game/Online/API/Requests/GetMessagesRequest.cs

// Copyright (c) 2007-2017 ppy Pty Ltd <contact@ppy.sh>.
// Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE

using System.Collections.Generic;
using System.Linq;
using osu.Framework.IO.Network;
using osu.Game.Online.Chat;

namespace osu.Game.Online.API.Requests
{
    public class GetMessagesRequest : APIRequest<List<Message>>
    {
        private readonly List<Channel> channels;
        private long? since;

        public GetMessagesRequest(List<Channel> channels, long? sinceId)
        {
            this.channels = channels;
            since = sinceId;
        }

        protected override WebRequest CreateWebRequest()
        {
            string channelString = string.Join(",", channels.Select(x => x.Id));

            var req = base.CreateWebRequest();
            req.AddParameter(@"channels", channelString);
            if (since.HasValue) req.AddParameter(@"since", since.Value.ToString());

            return req;
        }

        protected override string Target => @"chat/messages";
    }
}