using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Linq;
using System.Net;
using System.Web;

using Amazon.SimpleNotificationService.Util;

namespace WebSNSReceiver
{
    /// <summary>
    /// Summary description for SNSReceiver
    /// </summary>
    public class SNSReceiver : IHttpHandler
    {
        public void ProcessRequest(HttpContext context)
        {
            if(context.Request.HttpMethod == "POST")
            {
                ProcessPost(context);
            }
            else if (context.Request.HttpMethod == "GET")
            {
                ProcessGet(context);
            }
        }

        private void ProcessGet(HttpContext context)
        {
            context.Response.ContentType = "text/plain";
            var log = context.Application["log"] as IList<string>;
            if (log == null)
            {
                context.Response.Write("No log messages");
            }
            else
            {
                foreach (var message in log.Reverse())
                {
                    context.Response.Write(message + "\n");
                }
            }
        }

        private void ProcessPost(HttpContext context)
        {
            string contentBody;
            using (StreamReader reader = new StreamReader(context.Request.InputStream))
                contentBody = reader.ReadToEnd();

            Message message = Message.ParseMessage(contentBody);

            if (!message.IsMessageSignatureValid())
                throw new Exception("Amazon SNS Message signature is invalid");

            if (message.IsSubscriptionType)
            {
                ConfirmSubscription(context, message);
            }
            else if (message.IsNotificationType)
            {
                ProcessNotification(context, message);
            }
        }

        private void ConfirmSubscription(HttpContext context, Message message)
        {
            if (!IsValidTopic(message.TopicArn))
                return;

            try
            {
                message.SubscribeToTopic();

                Trace.WriteLine(string.Format("Subscription to {0} confirmed.", message.TopicArn));
                var log = context.Application["log"] as IList<string>;
                if(log == null)
                {
                    log = new List<string>();
                    context.Application["log"] = log;
                }

                log.Add(string.Format("{0}: Confirmed subscription to {1}", DateTime.Now, message.TopicArn));
            }
            catch(Exception e)
            {
                Trace.WriteLine(string.Format("Error confirming subscription to {0}: {1}", message.TopicArn, e.Message));
            }
        }

        private bool IsValidTopic(string topicArn)
        {
            // Add whatever business logic needed to verify this is a topic that 
            // should be subscribed. This could be checking the account ID in the 
            // ARN for the topic.
            return true;
        }

        private void ProcessNotification(HttpContext context, Message message)
        {
            var log = context.Application["log"] as IList<string>;
            if (log == null)
            {
                log = new List<string>();
                context.Application["log"] = log;
            }

            log.Add(string.Format("{0}: Received notification from {1} with message {2}", DateTime.Now, message.TopicArn, message.MessageText));
        }

        public bool IsReusable
        {
            get
            {
                return false;
            }
        }
    }
}