TweetDuck/lib/TweetLib.Core/Features/Updates/UpdateHandler.cs

using System;
using System.Threading;
using System.Threading.Tasks;
using System.Timers;
using TweetLib.Core.Data;
using Timer = System.Timers.Timer;

namespace TweetLib.Core.Features.Updates{
    public sealed class UpdateHandler : IDisposable{
        public const int CheckCodeUpdatesDisabled = -1;
        
        private readonly IUpdateCheckClient client;
        private readonly TaskScheduler scheduler;
        private readonly Timer timer;
        
        public event EventHandler<UpdateCheckEventArgs> CheckFinished;
        private ushort lastEventId;

        public UpdateHandler(IUpdateCheckClient client, TaskScheduler scheduler){
            this.client = client;
            this.scheduler = scheduler;
            
            this.timer = new Timer{
                AutoReset = false,
                Enabled = false
            };

            this.timer.Elapsed += timer_Elapsed;
        }

        public void Dispose(){
            timer.Dispose();
        }

        private void timer_Elapsed(object sender, ElapsedEventArgs e){
            Check(false);
        }

        public void StartTimer(){
            if (timer.Enabled){
                return;
            }

            timer.Stop();

            if (client.CanCheck){
                DateTime now = DateTime.Now;
                TimeSpan nextHour = now.AddSeconds(60 * (60 - now.Minute) - now.Second) - now;

                if (nextHour.TotalMinutes < 15){
                    nextHour = nextHour.Add(TimeSpan.FromHours(1));
                }

                timer.Interval = (int)Math.Ceiling(nextHour.TotalMilliseconds);
                timer.Start();
            }
        }

        public int Check(bool force){
            if (client.CanCheck || force){
                int nextEventId = unchecked(++lastEventId);
                Task<UpdateInfo> checkTask = client.Check();

                checkTask.ContinueWith(task => HandleUpdateCheckSuccessful(nextEventId, task.Result), CancellationToken.None, TaskContinuationOptions.OnlyOnRanToCompletion, scheduler);
                checkTask.ContinueWith(task => HandleUpdateCheckFailed(nextEventId, task.Exception.InnerException), CancellationToken.None, TaskContinuationOptions.OnlyOnFaulted, scheduler);

                return nextEventId;
            }

            return CheckCodeUpdatesDisabled;
        }

        private void HandleUpdateCheckSuccessful(int eventId, UpdateInfo info){
            CheckFinished?.Invoke(this, new UpdateCheckEventArgs(eventId, new Result<UpdateInfo>(info)));
        }

        private void HandleUpdateCheckFailed(int eventId, Exception exception){
            CheckFinished?.Invoke(this, new UpdateCheckEventArgs(eventId, new Result<UpdateInfo>(exception)));
        }
    }
}