fixed ruby syntax with linter

app/helpers/application_helper.rb

@@ -1,3 +1,6 @@
+# frozen_string_literal: true
+
+# Various helpers methods
 module ApplicationHelper
 
   include Twitter::Autolink
@@ -19,7 +22,7 @@ module ApplicationHelper
     { flash: 'alert-success', alert: 'alert-danger', notice: 'alert-info' }[flash_type.to_sym] || flash_type.to_s
   end
 
-	def flash_messages(opts = {})
+  def flash_messages(_opts = {})
     flash.each do |msg_type, message|
       concat(content_tag(:div, message, class: "flash-message alert #{bootstrap_class_for(msg_type)} fade in") do
                concat content_tag(:button, 'x', class: 'close', data: { dismiss: 'alert' })
@@ -35,9 +38,9 @@ module ApplicationHelper
 
   def class_exists?(class_name)
     klass = Module.const_get(class_name)
-		return klass.is_a?(Class)
+    klass.is_a?(Class)
   rescue NameError
-		return false
+    false
   end
 
   ##
@@ -56,7 +59,7 @@ module ApplicationHelper
   end
 
   def bool_to_sym(bool)
-		if (bool) then return :true else return :false end
+    bool ? :true : :false # rubocop:disable Lint/BooleanSymbol
   end
 
   def amount_to_f(amount)
@@ -73,8 +76,8 @@ module ApplicationHelper
     array.each do |i|
       if key.nil?
         return i if i.id == id
-			else
-				return i if i[key] == id
+      elsif i[key] == id
+        return i
       end
     end
     nil
@@ -88,21 +91,20 @@ module ApplicationHelper
   ##
   def dst_correction(reference, datetime)
     res = datetime.in_time_zone(reference.time_zone.tzinfo.name)
-		res = res - 1.hour if res.dst? && !reference.dst?
-		res = res + 1.hour if reference.dst? && !res.dst?
+    res -= 1.hour if res.dst? && !reference.dst?
+    res += 1.hour if reference.dst? && !res.dst?
     res
   end
 
 
   private
+
   ## inspired by gems/actionview-4.2.5/lib/action_view/helpers/translation_helper.rb
   def scope_key_by_partial(key)
-		if key.to_s.first == "."
-			if @virtual_path
-				@virtual_path.gsub(%r{/_?}, ".") + key.to_s
-			else
-				raise "Cannot use t(#{key.inspect}) shortcut because path is not available"
-			end
+    if key.to_s.first == '.'
+      raise "Cannot use t(#{key.inspect}) shortcut because path is not available" unless @virtual_path
+
+      @virtual_path.gsub(%r{/_?}, '.') + key.to_s
     else
       key
     end

app/helpers/availability_helper.rb

@@ -1,3 +1,6 @@
+# frozen_string_literal: true
+
+# Helpers methods about calendar availabilities
 module AvailabilityHelper
   MACHINE_COLOR = '#e4cd78'
   TRAINING_COLOR = '#bd7ae9'

app/helpers/upload_helper.rb

@@ -1,3 +1,6 @@
+# frozen_string_literal: true
+
+# Helpers methods about uploading files
 module UploadHelper
 
   def delete_empty_dirs