// Zaxaa ZPN Sample Code for ASP.NET C#

using System;
using System.IO;
using System.Text;
using System.Net;
using System.Web;
using System.Security.Cryptography;

public partial class ZpnSample : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        // Your Zaxaa API Signature here
        String apiSignature = "<YOUR_ZAXAA_API_SIGNATURE>"; 
        
        // Grab transaction type 
        String transType = Request["trans_type"];
        if(! string.IsNullOrEmpty(transType)) {
            
            // Read POST data and validate ZPN
            String transReceipt     = Request["trans_receipt"];
	        String transAmount      = Request["trans_amount"];
	        String sellerID         = Request["seller_id"];
	        String hashKey          = Request["hash_key"];

            int itemCount = int.Parse(Request["item_count"]);

            String myHashKey = GetMd5Hash(sellerID + apiSignature + transReceipt + transAmount).ToUpper();

            if(myHashKey == hashKey) {
                // ZPN is valid
		        // Do something...
		
		        // You can do more validation like matching your seller ID
		        // or matching your email address...
		        // or validate the received amount...

		        switch ( transType ) {
			        case "SALE":
				        // New payment for one-time product(s)
                        for (int i=0; i<itemCount; i++) {
                            // This ZPN may contain a payment for multiple products
					        // do something for each of the product here..
                            String sku = Request["products[" + i + "][prod_number]"];
                            // do something...
                        }
				        break;
			
			        case "FIRST_BILL":
				        // New payment for a subscription product(s)
                        for (int i=0; i<itemCount; i++) {
                            // This ZPN may contain a payment for multiple products
					        // do something for each of the product here...
                            String sku = Request["products[" + i + "][prod_number]"];
                            String paymentType = Request["products[" + i + "][payment_type]"];

                            // NOTE: If this is a ZPN for OTO with a subscription product,
					        // then this ZPN may also contain information for one-time product(s)
					        if ( paymentType == "subscription" ) {
						        // The product is a subscription
						        // do something...
					        } else if ( paymentType == "onetime" ) {
						        // The product is a one-time...
						        // do something...
					        }
                        }
				        break;
				
			        case "REBILL":
				        // Recurring payment received
                        for (int i=0; i<itemCount; i++) {
                            String sku = Request["products[" + i + "][prod_number]"];
                            String recurringId = Request["products[" + i + "][recurring_id]"]; // This might be useful to recognize past recurring payments
                            // do something...
                        }
				        break;
				
			        case "CANCELED":
				        // Subscription is canceled
				        for (int i=0; i<itemCount; i++) {
                            String sku = Request["products[" + i + "][prod_number]"];
                            String recurringId = Request["products[" + i + "][recurring_id]"]; // This might be useful to recognize past recurring payments
                            // do something...
                        }
				        break;
				
			        case "REFUND":
				        // Refunded payment...
				        for (int i=0; i<itemCount; i++) {
                            String sku = Request["products[" + i + "][prod_number]"];
                            // do something...
                        }
				        break;
		        }
	        } else {
		        // ZPN is Invalid
		        // log for manual investigation
	        }
        }
    }

    public static string GetMd5Hash(string input)
    {
        MD5 md5Hash = MD5.Create();
        // Convert the input string to a byte array and compute the hash.
        byte[] data = md5Hash.ComputeHash(Encoding.UTF8.GetBytes(input));

        // Create a new Stringbuilder to collect the bytes
        // and create a string.
        StringBuilder sBuilder = new StringBuilder();

        // Loop through each byte of the hashed data 
        // and format each one as a hexadecimal string.
        for (int i = 0; i < data.Length; i++)
        {
            sBuilder.Append(data[i].ToString("x2"));
        }

        // Return the hexadecimal string.
        return sBuilder.ToString();
    }
}