Refine constructor parameter population for model factory (Azure#53099)

* Refine constructor parameter population for model factory

* update doc

* refine to avoid infinite loop

Author: live1206

eng/packages/http-client-csharp-mgmt/generator/Azure.Generator.Management/src/Visitors/FlattenPropertyVisitor.cs

@@ -175,24 +175,31 @@ private ValueExpression[] BuildConstructorParameters(CSharpType propertyType, Li
 
             var parameters = new List<ValueExpression>();
             var additionalPropertyIndex = GetAdditionalPropertyIndex();
-            for (int i = 0, fullConstructorParameterIndex = 0; i < flattenedProperties.Count; i++, fullConstructorParameterIndex++)
+            for (int flattenedPropertyIndex = 0, fullConstructorParameterIndex = 0; ; fullConstructorParameterIndex++)
             {
-                if (i == additionalPropertyIndex)
+                // If we have processed all the flattened properties or all the constructor parameters, we can break the loop.
+                if (flattenedPropertyIndex >= flattenedProperties.Count || fullConstructorParameterIndex >= fullConstructorParameters.Count)
+                {
+                    break;
+                }
+
+                if (fullConstructorParameterIndex == additionalPropertyIndex)
                 {
                     // If the additionalProperties parameter exists, we need to pass a new instance for it.
                     parameters.Add(New.Instance(new CSharpType(typeof(Dictionary<string, BinaryData>))));
 
                     // If the additionalProperties parameter is the last parameter, we can break the loop.
-                    if (additionalPropertyIndex == fullConstructorParameters.Count - 1)
+                    if (fullConstructorParameterIndex == fullConstructorParameters.Count - 1)
                     {
                         break;
                     }
                     fullConstructorParameterIndex++;
                 }
-                var (isOverriddenValueType, flattenedProperty) = flattenedProperties[i];
+                var (isOverriddenValueType, flattenedProperty) = flattenedProperties[flattenedPropertyIndex];
                 var propertyParameter = flattenedProperty.AsParameter;
                 var flattenedPropertyType = flattenedProperty.Type;
                 var constructorParameterType = fullConstructorParameters[fullConstructorParameterIndex].Type;
+
                 // If the internal property type is the same as the property type, we can use the flattened property directly.
                 if (constructorParameterType.AreNamesEqual(flattenedPropertyType))
                 {
@@ -204,6 +211,8 @@ private ValueExpression[] BuildConstructorParameters(CSharpType propertyType, Li
                     {
                         parameters.Add(isOverriddenValueType ? propertyParameter.Property("Value") : propertyParameter);
                     }
+                    // only increase flattenedPropertyIndex when we use a flattened property
+                    flattenedPropertyIndex++;
                 }
                 else
                 {
@@ -219,8 +228,8 @@ private ValueExpression[] BuildConstructorParameters(CSharpType propertyType, Li
                 }
             }
 
-            // If the additionalProperties parameter exists at the end, we need to pass a new instance for it.
-            if (additionalPropertyIndex == propertyModelType!.FullConstructor.Signature.Parameters.Count - 1)
+            // If the additionalProperties parameter is missing at the end, we need to pass a new instance for it.
+            if (parameters.Count < fullConstructorParameters.Count && additionalPropertyIndex == propertyModelType!.FullConstructor.Signature.Parameters.Count - 1)
             {
                 parameters.Add(New.Instance(new CSharpType(typeof(Dictionary<string, BinaryData>))));
             }