Add --keep-num-emails to only keep that many emails and delete oldest

lib/mail_catcher.rb

@@ -82,6 +82,7 @@ module MailCatcher extend self
     :quit => true,
     :sqlite_db => ':memory:',
     :delete_older_than => nil,
+    :keep_num_emails => nil,
   }
 
   def options
@@ -130,6 +131,10 @@ module MailCatcher extend self
           options[:delete_older_than] = db
         end
 
+        parser.on("--keep-num-emails MAX_EMAILS", "Only keep this many emails, deletes oldest") do |db|
+          options[:keep_num_emails] = db
+        end
+
         if mac?
           parser.on("--[no-]growl") do |growl|
             puts "Growl is no longer supported"

lib/mail_catcher/mail.rb

@@ -60,6 +60,9 @@ module MailCatcher::Mail extend self
       if MailCatcher.options[:delete_older_than]
         MailCatcher::Mail.delete_messages_older_than!(MailCatcher.options[:delete_older_than])
       end
+      if MailCatcher.options[:keep_num_emails]
+        MailCatcher::Mail.delete_messages_keep!(MailCatcher.options[:keep_num_emails])
+      end
     end
   end
 
@@ -169,4 +172,11 @@ module MailCatcher::Mail extend self
     @delete_messages_older_than_query.execute(modifier) and
     @delete_message_parts_older_than_query.execute(modifier)
   end
+
+  def delete_messages_keep!(keep_num_emails)
+    @delete_messages_query ||= db.prepare "DELETE FROM message WHERE id IN (SELECT id FROM message ORDER BY id DESC LIMIT -1 OFFSET ?);"
+    @delete_message_parts_query ||= db.prepare "DELETE FROM message_part WHERE id NOT IN (SELECT id FROM message)"
+    @delete_messages_query.execute(keep_num_emails) and
+    @delete_message_parts_query.execute()
+  end
 end