convert format_hours_period helper to format_hours_semester helper

- and also display "1. Semester 2018 - 2. Semester 2019"

app/helpers/format_helper.rb

@@ -8,10 +8,35 @@ module FormatHelper
     pluralize hours, 'Stunde', 'Stunden'
   end
 
-  def format_hours_period(hours)
+  def format_hours_semester(hours)
     return '' if hours.blank?
-
     dates = hours.map(&:meeting_date)
-    "#{I18n.l dates.min} - #{I18n.l dates.max}"
+    if dates.size == 1
+      "#{BillingExpense.semester_of_year(dates.first)}. Semester #{semester_display_year(dates.first)}"
+    else
+      format_hours_multiple_dates_semester(dates)
+    end
+  end
+
+  def format_hours_multiple_dates_semester(dates)
+    min_date = dates.min
+    max_date = dates.max
+    if semester_display_year(min_date) != semester_display_year(max_date)
+      "#{BillingExpense.semester_of_year(min_date)}. Semester #{semester_display_year(min_date)} - "\
+        "#{BillingExpense.semester_of_year(max_date)}. Semester #{max_date.year}"
+    elsif BillingExpense.semester_of_year(min_date) == BillingExpense.semester_of_year(max_date)
+      "#{BillingExpense.semester_of_year(max_date)}. Semester #{semester_display_year(max_date)}"
+    else
+      "#{BillingExpense.semester_of_year(min_date)}. - "\
+        "#{BillingExpense.semester_of_year(max_date)}. Semester #{semester_display_year(max_date)}"
+    end
+  end
+
+  def semester_display_year(date)
+    if date.month == 12
+      date.year + 1
+    else
+      date.year
+    end
   end
 end

test/helpers/format_helper_test.rb

@@ -14,10 +14,21 @@ class FormatHelperTest < ActionView::TestCase
   end
 
   test 'format_hours_period' do
-    assert_equal '01.02.2013 - 03.04.2015', format_hours_period([
+    assert_equal '1. Semester 2013 - 1. Semester 2015', format_hours_semester([
       create(:hour, meeting_date: '2015-04-03'),
       create(:hour, meeting_date: '2014-05-06'),
-      create(:hour, meeting_date: '2013-02-01')
+      create(:hour, meeting_date: '2012-12-01')
+    ])
+    assert_equal '1. - 2. Semester 2015', format_hours_semester([
+      create(:hour, meeting_date: '2015-04-03'),
+      create(:hour, meeting_date: '2015-09-06')
+    ])
+    assert_equal '1. Semester 2015', format_hours_semester([
+      create(:hour, meeting_date: '2015-04-03'),
+      create(:hour, meeting_date: '2015-04-06')
+    ])
+    assert_equal '1. Semester 2015', format_hours_semester([
+      create(:hour, meeting_date: '2015-04-03')
     ])
   end
 end