From c3bbf344994eb5fa5e682cae177b9f59b685699d Mon Sep 17 00:00:00 2001
From: Tan Yi Xian <>
Date: Fri, 28 Oct 2022 03:52:34 +0800
Subject: [PATCH] Modify view to show error for negative index

---
 .../seedu/foodrem/commons/util/StringUtil.java   | 16 ++++++++++++++--
 .../itemcommandparser/ViewCommandParser.java     | 11 +++++++++++
 2 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/src/main/java/seedu/foodrem/commons/util/StringUtil.java b/src/main/java/seedu/foodrem/commons/util/StringUtil.java
index 4cc6fcc2052..09388c45097 100644
--- a/src/main/java/seedu/foodrem/commons/util/StringUtil.java
+++ b/src/main/java/seedu/foodrem/commons/util/StringUtil.java
@@ -83,11 +83,23 @@ public static String getDetails(Throwable t) {
      * @throws NullPointerException if {@code s} is null.
      */
     public static boolean isNonZeroUnsignedInteger(String s) {
+        return isInteger(s) && Integer.parseInt(s) > 0;
+    }
+
+    /**
+     * Returns {@code true} if {@code s} represents an integer
+     * e.g. {@code Integer.MIN_VALUE} -3, -2, -1, 0, 1, 2, 3, ..., {@code Integer.MAX_VALUE} <br>
+     * Will return {@code false} for any other non-null string input
+     * e.g. empty string, "0", "+1", and " 2 " (untrimmed), "3 0" (contains whitespace), "1 a" (contains letters)
+     *
+     * @throws NullPointerException if {@code s} is null.
+     */
+    public static boolean isInteger(String s) {
         requireNonNull(s);
 
         try {
-            int value = Integer.parseInt(s);
-            return value > 0 && !s.startsWith("+"); // "+1" is successfully parsed by Integer#parseInt(String)
+            Integer.parseInt(s);
+            return !s.startsWith("+"); // "+1" is successfully parsed by Integer#parseInt(String)
         } catch (NumberFormatException nfe) {
             return false;
         }
diff --git a/src/main/java/seedu/foodrem/logic/parser/itemcommandparser/ViewCommandParser.java b/src/main/java/seedu/foodrem/logic/parser/itemcommandparser/ViewCommandParser.java
index a7cb322c658..c7d77116883 100644
--- a/src/main/java/seedu/foodrem/logic/parser/itemcommandparser/ViewCommandParser.java
+++ b/src/main/java/seedu/foodrem/logic/parser/itemcommandparser/ViewCommandParser.java
@@ -4,6 +4,7 @@
 
 import seedu.foodrem.commons.core.Messages;
 import seedu.foodrem.commons.core.index.Index;
+import seedu.foodrem.commons.util.StringUtil;
 import seedu.foodrem.logic.commands.itemcommands.ViewCommand;
 import seedu.foodrem.logic.parser.Parser;
 import seedu.foodrem.logic.parser.ParserUtil;
@@ -23,6 +24,16 @@ public ViewCommand parse(String args) throws ParseException {
         requireNonNull(args);
         Index index;
 
+        String trimmedArgument = args.trim();
+
+        if (!StringUtil.isInteger(trimmedArgument)) {
+            throw new ParseException(String.format(Messages.MESSAGE_INVALID_COMMAND_FORMAT, ViewCommand.getUsage()));
+        }
+
+        if (!StringUtil.isNonZeroUnsignedInteger(trimmedArgument)) {
+            throw new ParseException("The index should be a non-negative number.");
+        }
+
         try {
             index = ParserUtil.parseIndex(args);
         } catch (ParseException pe) {