Refactored the way amount of billing expenses is calculated to...

...be calculated automaticly before_validation

app/controllers/billing_expenses_controller.rb

 class BillingExpensesController < ApplicationController
   before_action :set_billing_expense, only: [:show, :destroy]
   before_action :set_volunteer
-  before_action :set_volunteer_hours, only: :create
-  after_action :volunteer_hours_update, only: :create
 
   def index
     authorize BillingExpense
@@ -13,10 +11,7 @@ class BillingExpensesController < ApplicationController
     respond_to do |format|
       format.html
       format.pdf do
-        render pdf:
-          "Spesenauszahlung-#{@volunteer.contact.first_name}-#{@volunteer.contact.last_name}-#{@volunteer.hours.last.meeting_date}",
-          template: 'billing_expenses/show.html.slim',
-          layout: 'pdf.pdf', encoding: 'UTF-8'
+        render pdf: file_name, layout: 'pdf.pdf', encoding: 'UTF-8'
       end
     end
   end
@@ -29,8 +24,9 @@ class BillingExpensesController < ApplicationController
   def create
     @billing_expense = BillingExpense.new(
       billing_expense_params.merge(@volunteer.slice(:bank, :iban))
-                            .merge(amount: compute_hours, user_id: current_user.id)
     )
+    @billing_expense.hours = @volunteer.hours.billable
+    @billing_expense.user = current_user
     authorize @billing_expense
     if @billing_expense.save
       redirect_to volunteer_billing_expenses_url, make_notice
@@ -55,27 +51,8 @@ class BillingExpensesController < ApplicationController
     @volunteer = Volunteer.find(params[:volunteer_id]) if params[:volunteer_id]
   end
 
-  def set_volunteer_hours
-    @volunteer_hours = @volunteer.hours.where(billing_expense: nil)
-  end
-
-  def compute_hours
-    return if @volunteer_hours.empty?
-    compute_amount(@volunteer_hours.sum(&:hours) + @volunteer_hours.sum(&:minutes)/60)
-  end
-
-  def compute_amount(hours)
-    if hours < 25
-      50
-    elsif hours < 50
-      100
-    else
-      150
-    end
-  end
-
-  def volunteer_hours_update
-    @volunteer_hours.update(billing_expense_id: @billing_expense.id)
+  def file_name
+    [@volunteer.contact.full_name, @volunteer.hours.maximum(:meeting_date)].join('-').parameterize
   end
 
   def billing_expense_params

app/models/billing_expense.rb

 class BillingExpense < ApplicationRecord
   include FullBankDetails
 
+  before_validation :compute_amount
   belongs_to :volunteer
   belongs_to :user, -> { with_deleted }
   has_many :hours
 
   default_scope { order(created_at: :desc) }
 
-  AMOUNT = [50, 100, 150].freeze
+  AMOUNT = [0, 50, 100, 150].freeze
 
   validates :amount, inclusion: { in: AMOUNT }
 
@@ -19,4 +20,25 @@ class BillingExpense < ApplicationRecord
   def billed_hours
     Hour.where(billing_expense: id)
   end
+
+  def amount=(_value)
+    super(compute_amount)
+  end
+
+  def compute_amount
+    hour_count = id ? hours_sum : volunteer.billable_hours_sum
+    if hour_count > 50
+      150
+    elsif hour_count > 25
+      100
+    elsif hour_count >= 1
+      50
+    else
+      0
+    end
+  end
+
+  def hours_sum
+    hours.sum(&:hours) + hours.sum(&:minutes) / 60
+  end
 end

app/models/hour.rb

@@ -8,6 +8,8 @@ class Hour < ApplicationRecord
   validates :hours, presence: true, numericality: { greater_than_or_equal_to: 0 }
   validates :meeting_date, presence: true
 
+  scope :billable, (-> { where(billing_expense: nil) })
+
   HOUR_RANGE = (1..8).to_a
   MINUTE_RANGE = [0, 15, 30, 45].freeze
 end

app/models/volunteer.rb

@@ -71,6 +71,10 @@ class Volunteer < ApplicationRecord
 
   scope :with_hours, (-> { joins(:hours).distinct })
 
+  def billable_hours_sum
+    hours.billable.sum(&:hours) + hours.billable.sum(&:minutes) / 60
+  end
+
   def hours_sum
     hours.sum(&:hours) + hours.sum(&:minutes) / 60
   end

app/views/billing_expenses/show.pdf.slim

+= render 'billing_expenses/show.html.slim'