fix: extract form values directly from form fields to preserve them

- Change get_existing_form_values to read from form[:field].value
- This ensures current form state is preserved when only interval changes
- Fixes issue where name and amount were cleared on interval selection

lib/mv_web/live/membership_fee_type_live/form.ex

@@ -208,6 +208,7 @@ defmodule MvWeb.MembershipFeeTypeLive.Form do
   @impl true
   def handle_event("validate", %{"membership_fee_type" => params}, socket) do
     # Merge with existing form values to preserve unchanged fields
+    # Extract values directly from form fields to get current state
     existing_values = get_existing_form_values(socket.assigns.form)
 
     # Merge existing values with new params (new params take precedence)
@@ -323,25 +324,55 @@ defmodule MvWeb.MembershipFeeTypeLive.Form do
 
   # Helper to extract existing form values to preserve them when only one field changes
   defp get_existing_form_values(form) do
-    # Get current form values from the form source
-    case form.source.params do
-      %{"membership_fee_type" => existing_params} when is_map(existing_params) ->
-        # Convert atoms to strings for form params
-        existing_params
-        |> Enum.map(fn
-          {key, value} when is_atom(key) -> {Atom.to_string(key), value}
-          {key, value} -> {key, value}
-        end)
-        |> Enum.map(fn
-          {key, value} when is_atom(value) -> {key, Atom.to_string(value)}
-          {key, value} -> {key, value}
-        end)
-        |> Map.new()
+    # Extract values directly from form fields to get current state
+    # This ensures we get the actual current values, not just initial params
+    existing_values = %{}
 
-      _ ->
-        # No existing params, return empty map
-        %{}
-    end
+    existing_values =
+      if form[:name] && form[:name].value do
+        Map.put(existing_values, "name", to_string(form[:name].value))
+      else
+        existing_values
+      end
+
+    existing_values =
+      if form[:amount] && form[:amount].value do
+        # Convert Decimal to string for form
+        amount_str =
+          case form[:amount].value do
+            %Decimal{} = amount -> Decimal.to_string(amount, :normal)
+            value when is_binary(value) -> value
+            value -> to_string(value)
+          end
+
+        Map.put(existing_values, "amount", amount_str)
+      else
+        existing_values
+      end
+
+    existing_values =
+      if form[:interval] && form[:interval].value do
+        # Convert atom to string for form
+        interval_str =
+          case form[:interval].value do
+            value when is_atom(value) -> Atom.to_string(value)
+            value when is_binary(value) -> value
+            value -> to_string(value)
+          end
+
+        Map.put(existing_values, "interval", interval_str)
+      else
+        existing_values
+      end
+
+    existing_values =
+      if form[:description] && form[:description].value do
+        Map.put(existing_values, "description", to_string(form[:description].value))
+      else
+        existing_values
+      end
+
+    existing_values
   end
 
   @spec return_path(String.t(), MembershipFeeType.t() | nil) :: String.t()