Update Measurements#new form pathnames on actions

app/controllers/measurements_controller.rb

@@ -1,14 +1,12 @@
 class MeasurementsController < ApplicationController
-  before_action :find_quantity, only: [:new]
+  before_action :find_quantity, only: [:new, :discard]
+  before_action :find_prev_quantities, only: [:new, :discard]
 
   def index
     @quantities = current_user.quantities.ordered
   end
 
   def new
-    prev_quantity_ids = params[:readouts]&.map { |r| r[:quantity_id] } || []
-    @prev_quantities = current_user.quantities.find(prev_quantity_ids)
-
     quantities =
       case params[:scope]
       when 'children'
@@ -21,12 +19,18 @@ class MeasurementsController < ApplicationController
     quantities -= @prev_quantities
     @readouts = current_user.readouts.build(quantities.map { |q| {quantity: q} })
 
-    all_quantities = @prev_quantities + quantities
-    @closest_ancestor = current_user.quantities
-      .common_ancestors(all_quantities.map(&:parent_id)).first
-    all_quantities << @closest_ancestor if @closest_ancestor
-
     @units = current_user.units.ordered
+
+    all_quantities = @prev_quantities + quantities
+    @common_ancestor = current_user.quantities
+      .common_ancestors(all_quantities.map(&:parent_id)).first
+  end
+
+  def discard
+    @prev_quantities -= [@quantity]
+
+    @common_ancestor = current_user.quantities
+      .common_ancestors(@prev_quantities.map(&:parent_id)).first
   end
 
   def create
@@ -40,4 +44,9 @@ class MeasurementsController < ApplicationController
   def find_quantity
     @quantity = current_user.quantities.find_by!(id: params[:id])
   end
+
+  def find_prev_quantities
+    prev_quantity_ids = params[:readouts]&.map { |r| r[:quantity_id] } || []
+    @prev_quantities = current_user.quantities.find(prev_quantity_ids)
+  end
 end