allow negative amounts to swap creditor and debtor

app/models/transaction.rb

@@ -24,6 +24,14 @@ class Transaction < ActiveRecord::Base
   validates :amount, numericality: { greater_than: 0 }
   validate :different_debtor_creditor
 
+  def initialize *args, **kwargs
+    super *args, **kwargs
+    if amount < 0
+      self.creditor, self.debtor = debtor, creditor
+      self.amount = self.amount.abs
+    end
+  end
+
   def peer_of(user)
     return creditor if user == debtor
     return debtor if user == creditor

app/views/transactions/_new.html.haml

@@ -3,11 +3,7 @@
 = render 'partials/form_errors', object: @transaction
 
 = form_for @transaction, remote: true, html: { class: "pure-form form-inline" } do |f|
-  - if current_user.penning
-    = f.collection_select :debtor, User.all, :name, :name,
-        { selected: @transaction.debtor.try(:name) || current_user.name }, { class: 'select2-selector form-control'}
-  - else
-    = f.hidden_field :debtor, value: current_user.name
+  = f.hidden_field :debtor, value: @user.name
   = f.select :creditor,
       options_from_collection_for_select(User.all.order(:name), :name, :name),
       { include_blank: true },
@@ -19,6 +15,7 @@
     %span.input-group-addon
       %span.glyphicon.glyphicon-euro
     = f.number_field :euros, value: amount(@transaction.amount),
-        placeholder: "Bedrag", step: 0.01, min: 0.01, class: "form-control", size: 20
+        placeholder: "Bedrag", step: 0.01, min: (0.01 unless current_user.penning),
+        class: "form-control", size: 20
     -# placeholder: "Bedrag", step: 0.01, min: 0.01, class: "pure-group-addon price", size: 20, required: true
   = f.submit "Send it!", class: "pure-button pure-button-primary"