From b27b78f24d754ef9528d3a1a959014ece5d0b1c7 Mon Sep 17 00:00:00 2001
From: CeciliaAvila <cecilia.avila@southworks.com>
Date: Thu, 17 Oct 2024 14:11:33 -0300
Subject: [PATCH] Create deterministic GeHashCode method

---
 .../CosmosDBKeyEscape.cs                      | 34 ++++++++++++++++++-
 .../CosmosDBKeyEscapeTests.cs                 |  4 ++-
 2 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/libraries/Microsoft.Bot.Builder.Azure/CosmosDBKeyEscape.cs b/libraries/Microsoft.Bot.Builder.Azure/CosmosDBKeyEscape.cs
index e6e154d669..c191315941 100644
--- a/libraries/Microsoft.Bot.Builder.Azure/CosmosDBKeyEscape.cs
+++ b/libraries/Microsoft.Bot.Builder.Azure/CosmosDBKeyEscape.cs
@@ -117,11 +117,43 @@ private static string TruncateKeyIfNeeded(string key, bool truncateKeysForCompat
 
             if (key.Length > MaxKeyLength)
             {
-                var hash = key.GetHashCode().ToString("x", CultureInfo.InvariantCulture);
+                var hash = key.GetDeterministicHashCode().ToString("x", CultureInfo.InvariantCulture);
                 key = key.Substring(0, MaxKeyLength - hash.Length) + hash;
             }
 
             return key;
         }
+
+        /// <summary>
+        /// Creates a deterministic hash code by iterating through the string two characters at a time,
+        /// updating two separate hash values, and then combining them at the end.
+        /// This approach helps in reducing hash collisions and provides a consistent hash code for the same string across
+        /// different runs and environments.
+        /// </summary>
+        /// <param name="str">The string to calculate the hash on.</param>
+        /// <returns>The hash code.</returns>
+        private static int GetDeterministicHashCode(this string str)
+        {
+            unchecked
+            {
+                var hash1 = (5381 << 16) + 5381; //shifts 5381 left by 16 bits and adds 5381 to it
+                var hash2 = hash1;
+                for (var i = 0; i < str.Length; i += 2)
+                {
+                    // ((hash1 << 5) + hash1) is equivalent to hash1 * 33, which is a common multiplier in hash functions.
+                    // The character str[i] is then XORed with this value.
+                    hash1 = ((hash1 << 5) + hash1) ^ str[i]; 
+                    if (i == str.Length - 1)
+                    {
+                        break;
+                    }
+
+                    hash2 = ((hash2 << 5) + hash2) ^ str[i + 1];
+                }
+
+                //1566083941 is a large prime number used to mix the two hash values together, ensuring a more uniform distribution of hash codes.
+                return hash1 + (hash2 * 1566083941);
+            }
+        }
     }
 }
diff --git a/tests/Microsoft.Bot.Builder.Azure.Tests/CosmosDBKeyEscapeTests.cs b/tests/Microsoft.Bot.Builder.Azure.Tests/CosmosDBKeyEscapeTests.cs
index 1f5ec6f3f2..f924bde1f8 100644
--- a/tests/Microsoft.Bot.Builder.Azure.Tests/CosmosDBKeyEscapeTests.cs
+++ b/tests/Microsoft.Bot.Builder.Azure.Tests/CosmosDBKeyEscapeTests.cs
@@ -2,6 +2,7 @@
 // Licensed under the MIT License.
 
 using System;
+using System.Reflection;
 using Xunit;
 
 namespace Microsoft.Bot.Builder.Azure.Tests
@@ -40,7 +41,8 @@ public void Long_Key_Should_Be_Truncated()
             Assert.True(sanitizedKey.Length <= CosmosDbKeyEscape.MaxKeyLength, "Key too long");
 
             // The resulting key should be:
-            var hash = tooLongKey.GetHashCode().ToString("x");
+            var getHashMethod = typeof(CosmosDbKeyEscape).GetMethod("GetDeterministicHashCode", BindingFlags.NonPublic | BindingFlags.Static);
+            var hash = ((int)getHashMethod.Invoke(null, new object[] { tooLongKey })).ToString("x");
             var correctKey = sanitizedKey.Substring(0, CosmosDbKeyEscape.MaxKeyLength - hash.Length) + hash;
 
             Assert.Equal(correctKey, sanitizedKey);