using System;
using System.Collections.Generic;
using System.Web;
using Microsoft.Ccr.Core;
using Roblox.Common;

namespace Roblox.Ccr
{
    public abstract class HttpModule : IHttpModule
    {
        protected abstract IEnumerator<ITask> Execute(HttpApplication httpApplication);

        private IAsyncResult BeginPreRequestHandlerExecute(object source, EventArgs e, AsyncCallback callback,
            object state)
        {
            var t = (HttpApplication) source;
            var result = new FastAsyncResult(callback, state);
            CcrService.Singleton.SpawnIterator(t, result, ExecuteAndComplete);
            return result;
        }

        private void EndPreRequestHandlerExecute(IAsyncResult result)
        {
            var fastResult = result as FastAsyncResult;
            if (fastResult != null)
            {
                var error = fastResult.Error;
                fastResult.Dispose();
                if (error != null) throw new ApplicationException("Roblox.Ccr.HttpModule Error", error);
            }
        }

        private IEnumerator<ITask> ExecuteAndComplete(HttpApplication httpApplication, FastAsyncResult result)
        {
            IEnumerator<ITask> en;

            try
            {
                en = Execute(httpApplication);
            }
            catch (Exception completed)
            {
                result.SetCompleted(completed);
                yield break;
            }

            using (en)
            {
                for (;;)
                {
                    try
                    {
                        if (!en.MoveNext())
                        {
                            result.SetCompleted();
                            yield break;
                        }
                    }
                    catch (Exception completed)
                    {
                        result.SetCompleted(completed);
                        yield break;
                    }

                    yield return en.Current;
                }
            }
        }
        
        public void Dispose() {}

        public void Init(HttpApplication application)
            => application.AddOnPreRequestHandlerExecuteAsync(BeginPreRequestHandlerExecute,
                EndPreRequestHandlerExecute);
    }
}