Allow email_prefix to be a proc

README.md

@@ -182,9 +182,9 @@ Who the message is destined for, can be a string of addresses, an array of addre
 
 ##### email_prefix
 
-*String, default: [ERROR]*
+*String/Proc, default: [ERROR]*
 
-The subject's prefix of the message.
+The subject's prefix of the message. It can be a proc that returns a string. The proc will be evaluated when the mail is sent.
 
 ##### sections
 

lib/exception_notifier/email_notifier.rb

@@ -20,6 +20,8 @@ def method_missing(*args, &block)
 
       def self.extended(base)
         base.class_eval do
+          attr_reader :env, :exception, :request, :data
+
           self.send(:include, ExceptionNotifier::BacktraceCleaner)
 
           # Append application view path to the ExceptionNotifier lookup context.
@@ -59,7 +61,7 @@ def background_exception_notification(exception, options={}, default_options={})
           private
 
           def compose_subject
-            subject = "#{@options[:email_prefix]}"
+            subject = "#{maybe_call(@options[:email_prefix])}"
             subject << "(#{@options[:accumulated_errors_count]} times)" if @options[:accumulated_errors_count].to_i > 1
             subject << "#{@kontroller.controller_name} #{@kontroller.action_name}" if @kontroller && @options[:include_controller_and_action_names_in_subject]
             subject << " (#{@exception.class})"
@@ -130,7 +132,8 @@ def load_custom_views
           end
 
           def maybe_call(maybe_proc)
-            maybe_proc.respond_to?(:call) ? maybe_proc.call : maybe_proc
+            return maybe_proc unless maybe_proc.respond_to?(:call)
+            (maybe_proc.arity == 0) ? maybe_proc.call : maybe_proc.call(self)
           end
         end
       end

test/exception_notifier/email_notifier_test.rb

@@ -219,6 +219,21 @@ class EmailNotifierTest < ActiveSupport::TestCase
     assert_equal %w{[email protected]}, mail.to
   end
 
+  test "should lazily evaluate email_prefix" do
+    email_prefixes = %w(first second)
+    email_notifier = ExceptionNotifier::EmailNotifier.new(
+      :email_prefix => -> { email_prefixes.shift },
+      :sender_address => %{"Dummy Notifier" <[email protected]>},
+      :exception_recipients => "[email protected]",
+      :delivery_method => :test,
+    )
+
+    mail = email_notifier.call(@exception)
+    assert_equal %|first (ZeroDivisionError) "divided by 0"|, mail.subject
+    mail = email_notifier.call(@exception)
+    assert_equal %|second (ZeroDivisionError) "divided by 0"|, mail.subject
+  end
+
   test "should prepend accumulated_errors_count in email subject if accumulated_errors_count larger than 1" do
     ActionMailer::Base.deliveries.clear