Refactored shasher payfast confirmation response handling

LiteCharms.Features/Hasher/HashService.cs

@@ -1,5 +1,6 @@
 using LiteCharms.Features.Abstractions;
 using LiteCharms.Features.Hasher.Configuration;
+using LiteCharms.Features.Models;
 
 namespace LiteCharms.Features.Hasher;
 
@@ -40,24 +41,30 @@ public sealed partial class HashService(IHashids hasher, IOptions<HasherSettings
         return Result.Ok(Convert.ToHexString(bytes).ToLowerInvariant());
     }
 
-    public Result<bool> VerifyPayfastWebhookSignature(IDictionary<string, string> incomingFormData, string incomingSignature)
+    public Result<bool> VerifyPayfastWebhookSignature(PayfastWebhookPayload payload, string incomingSignature)
     {
         try
         {
             if (string.IsNullOrWhiteSpace(incomingSignature))
                 return Result.Fail<bool>("Validation failed: Missing signature string parameter.");
 
-            var sortedFields = incomingFormData
-                .Where(field => !string.Equals(field.Key, "signature", StringComparison.OrdinalIgnoreCase))
-                .OrderBy(field => field.Key, StringComparer.Ordinal)
-                .Select(field => $"{field.Key}={WebUtility.UrlEncode(field.Value)}");
+            var parameters = new List<string>();
 
-            string payload = string.Join("&", sortedFields);
+            if (!string.IsNullOrWhiteSpace(payload.Amount))
+                parameters.Add($"amount={WebUtility.UrlEncode(payload.Amount)}");
+
+            if (!string.IsNullOrWhiteSpace(payload.ItemName))
+                parameters.Add($"item_name={WebUtility.UrlEncode(payload.ItemName)}");
+
+            if (!string.IsNullOrWhiteSpace(payload.MPaymentId))
+                parameters.Add($"m_payment_id={WebUtility.UrlEncode(payload.MPaymentId)}");
+
+            string signatureString = string.Join("&", parameters);
 
             if (!string.IsNullOrWhiteSpace(settings.PayfastPassphrase))
-                payload += $"&passphrase={WebUtility.UrlEncode(settings.PayfastPassphrase)}";
+                signatureString += $"&passphrase={WebUtility.UrlEncode(settings.PayfastPassphrase)}";
 
-            var localHashResult = ToMd5Hash(payload);
+            var localHashResult = ToMd5Hash(signatureString);
 
             if (!localHashResult.IsSuccess)
                 return Result.Fail<bool>(localHashResult.Errors);
@@ -68,7 +75,7 @@ public sealed partial class HashService(IHashids hasher, IOptions<HasherSettings
         }
         catch (Exception ex)
         {
-            return Result.Fail<bool>(new Error("An error occurred during MD5 verification loop.").CausedBy(ex));
+            return Result.Fail<bool>(new Error("An error occurred during Payfast MD5 verification.").CausedBy(ex));
         }
     }