Added exception if /to before /from

Author: DaDevChia

src/main/java/duke/parser/Parser.java

@@ -17,10 +17,12 @@
 import static duke.ui.MessageConstants.MESSAGE_ERROR_EMPTY_DESCRIPTION;
 import static duke.ui.MessageConstants.MESSAGE_ERROR_FROM_TIME_MISSING;
 import static duke.ui.MessageConstants.MESSAGE_ERROR_TO_TIME_MISSING;
+import static duke.ui.MessageConstants.MESSAGE_ERROR_TO_BEFORE_FROM;
 import static duke.ui.MessageConstants.MESSAGE_ERROR_DEADLINE_BY;
 import static duke.ui.MessageConstants.MESSAGE_ERROR_COMMAND;
 import static duke.ui.MessageConstants.MESSAGE_ERROR_FIND_MISSING;
 
+
 import static duke.parser.TaskConstants.DEADLINE;
 import static duke.parser.TaskConstants.EVENT;
 import static duke.parser.TaskConstants.TODO;
@@ -136,6 +138,10 @@ public static AddEventCommand parseEventCommand(String commandRawInput) throws D
             throw new DukeException(MESSAGE_ERROR_TO_TIME_MISSING);
         }
 
+        if (toPos < fromPos) {
+            throw new DukeException(MESSAGE_ERROR_TO_BEFORE_FROM);
+        }
+
         //get the task name
         String description = commandRawInput.substring(0,fromPos).trim();
 

src/main/java/duke/ui/MessageConstants.java

@@ -27,6 +27,7 @@ public class MessageConstants {
     public static final String MESSAGE_ERROR_EMPTY_DESCRIPTION = "☹ OOPS!!! The description of a task cannot be empty.";
     public static final String MESSAGE_ERROR_FROM_TIME_MISSING = "☹ OOPS!!! The /from time of an event cannot be empty.";
     public static final String MESSAGE_ERROR_TO_TIME_MISSING = "☹ OOPS!!! The /to time of an event cannot be empty.";
+    public static final String MESSAGE_ERROR_TO_BEFORE_FROM = "☹ OOPS!!! The /from time of an event must be typed before the /to time.";
     public static final String MESSAGE_ERROR_DEADLINE_BY = "☹ OOPS!!! The /by time of a deadline cannot be empty.";
     public static final String MESSAGE_ERROR_FIND_MISSING = "☹ OOPS!!! The word you are searching for cannot be empty.";
     public static final String MESSAGE_ERROR_FILE_CREATION = "☹ OOPS!!! Error creating file.";