using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

    public class RequestList
    {
        Dictionary<Guid, RequestMessage> requests;
        public RequestList()
        {
            requests = new Dictionary<Guid, RequestMessage>();
        }

        public void Add(RequestMessage request)
        {
            request.Status = MessageStatus.Pending;
            //Create a cancellation token source, this will be used to cancel a task
            request.RequestCancelToken = new CancellationTokenSource();
            requests.Add(request.MessageID, request);
            //Create and start a task and pass on the cancellation token to it
            var task = Task.Factory.StartNew(() =>
                //We also pass on the token to the operation for it access the token to check for
                //cancellation
                Process(request), request.RequestCancelToken.Token
            );

        }

        public void Cancel(RequestMessage request)
        {
            var dictRequestValue = (from x in requests
                          where x.Key == request.MessageID
                          select x).First().Value;

            dictRequestValue.RequestCancelToken.Cancel();
            dictRequestValue.Status = MessageStatus.Cancelled;
        }

        //This method contains the operation being executed by the task in parallel
        private static void Process(RequestMessage request)
        {
            request.Status = MessageStatus.Processing;
            CancellationToken token = request.RequestCancelToken.Token;

            //Check if cancellation is requested, using the token passed to the method
            //This check is for the case when cancellation might have been requested even before start of the
            //task
            if (token.IsCancellationRequested)
            {
                //This throws an OperationCanceledException if the token has had cancellation requested
                token.ThrowIfCancellationRequested();
            }

            //This simulates work
            var sw = new SpinWait();
            for (var i = 0; i < 1000; i++)
            {
                for (int j = 0; j < 50; j++)
                {
                    sw.SpinOnce();
                }
                //Check for requested cancellation amidst execution logic
                if (token.IsCancellationRequested)
                {
                    //This throws an OperationCanceledException if the token has had cancellation requested
                    token.ThrowIfCancellationRequested();
                }
            }
            //This code is reached if the task gets to complete prior to a cancellation request
            request.Status = MessageStatus.Done;
        }


}