Add safeguards around invalid drill states

lib/drill.rb

@@ -37,6 +37,8 @@ class Drill
   end
 
   def handle_join(message)
+    return respond "The drill's already started!" if running?
+
     if participants.include? message.author
       respond "You've already joined"
     else
@@ -46,6 +48,8 @@ class Drill
   end
 
   def handle_leave(message)
+    return respond "The drill's already started!" if running?
+
     if participants.include? message.author
       self.participants -= [message.author]
       respond "#{message.author.display_name} has left"
@@ -56,6 +60,7 @@ class Drill
 
   def handle_start(message)
     return respond "The drill's already started!" if running?
+    return respond "Nobody has joined the drill! Type `join` to join it!" if participants.empty?
 
     @running = true
     @time_is_up = false
@@ -68,9 +73,9 @@ class Drill
   def handle_stop(message)
     return respond "The drill's not running yet" unless running?
 
-    @running = false
     scheduler.unschedule(timer_job_id) if timer_job_id
-    respond "Drill stopped!"
+
+    end_drill!
   end
 
   def handle_customize_length(message)
@@ -105,6 +110,7 @@ class Drill
   def end_drill!
     respond "Time's up! Everyone did great!"
     @running = false
+    @participants = []
   end
 
   def generate_question