fix bug

app/helpers/exercises_helper.rb

@@ -682,17 +682,27 @@ module ExercisesHelper
   def get_exercise_left_time(exercise,user)
     ex_time = exercise.time
     user_left_time = nil
+    time_now_i = Time.now.to_i
     if ex_time > 0
       exercise_user = exercise.exercise_users.find_by(user_id:user.id)
       time_mill = ex_time * 60   #转为秒
       exercise_end_time = exercise.end_time.present? ? exercise.end_time.to_i : 0
       exercise_user_start = exercise_user.present? ? exercise_user.start_at.to_i : 0
+      #用户未开始答题时，即exercise_user_start为0
+      if exercise_user_start == 0
+        if (exercise_end_time - time_now_i) > time_mill
+          user_left_time = time_mill
+        else
+          user_left_time = (exercise_end_time < time_now_i) ? nil : (exercise_end_time - time_now_i)
+        end
+      else
         if (exercise_user_start + time_mill) > exercise_end_time
           time_mill = exercise_end_time - exercise_user_start   #如果开始答题时间加试卷的限时长大于试卷的截止时间，则以试卷的截止时间到开始答题时间为试卷的限时
         end
-      exercise_user_left_time = Time.now.to_i - exercise_user_start   #用户已回答的时间
+        exercise_user_left_time = time_now_i - exercise_user_start   #用户已回答的时间
         user_left_time = (time_mill < exercise_user_left_time) ? nil : (time_mill - exercise_user_left_time)   #当前用户对试卷的回答剩余时间
       end
+    end
     user_left_time
   end