KAFKA-4733: Improve Streams Reset Tool console output

Added general explanation of the tool and what it does. Also added few details to the arguments.

Author: Gwen Shapira <cshapi@gmail.com>

Reviewers: Matthias J. Sax, Michael G. Noll, Guozhang Wang

Closes #2503 from gwenshap/KAFKA-4733

core/src/main/scala/kafka/tools/StreamsResetter.java

@@ -138,12 +138,12 @@ public class StreamsResetter {
             .ofType(String.class)
             .defaultsTo("localhost:2181")
             .describedAs("url");
-        inputTopicsOption = optionParser.accepts("input-topics", "Comma-separated list of user input topics")
+        inputTopicsOption = optionParser.accepts("input-topics", "Comma-separated list of user input topics. For these topics, the tool will reset the offset to the earliest available offset.")
             .withRequiredArg()
             .ofType(String.class)
             .withValuesSeparatedBy(',')
             .describedAs("list");
-        intermediateTopicsOption = optionParser.accepts("intermediate-topics", "Comma-separated list of intermediate user topics")
+        intermediateTopicsOption = optionParser.accepts("intermediate-topics", "Comma-separated list of intermediate user topics (topics used in the through() method). For these topics, the tool will skip to the end.")
             .withRequiredArg()
             .ofType(String.class)
             .withValuesSeparatedBy(',')
@@ -152,7 +152,7 @@ public class StreamsResetter {
         try {
             options = optionParser.parse(args);
         } catch (final OptionException e) {
-            optionParser.printHelpOn(System.err);
+            printHelp(optionParser);
             throw e;
         }
     }
@@ -271,6 +271,26 @@ public class StreamsResetter {
             && (topicName.endsWith("-changelog") || topicName.endsWith("-repartition"));
     }
 
+    private void printHelp(OptionParser parser) throws IOException {
+        System.err.println("The Application Reset Tool allows you to quickly reset an application in order to reprocess "
+                + "its data from scratch.\n"
+                + "* This tool resets offsets of input topics to the earliest available offset and it skips to the end of "
+                + "intermediate topics (topics used in the through() method).\n"
+                + "* This tool deletes the internal topics that were created by Kafka Streams (topics starting with "
+                + "\"<application.id>-\").\n"
+                + "You do not need to specify internal topics because the tool finds them automatically.\n"
+                + "* This tool will not delete output topics (if you want to delete them, you need to do it yourself "
+                + "with the bin/kafka-topics.sh command).\n"
+                + "* This tool will not clean up the local state on the stream application instances (the persisted "
+                + "stores used to cache aggregation results).\n"
+                + "You need to call KafkaStreams#cleanUp() in your application or manually delete them from the "
+                + "directory specified by \"state.dir\" configuration (/tmp/kafka-streams/<application.id> by default).\n\n"
+                + "*** Important! You will get wrong output if you don't clean up the local stores after running the "
+                + "reset tool!\n\n"
+        );
+        parser.printHelpOn(System.err);
+    }
+
     public static void main(final String[] args) {
         Exit.exit(new StreamsResetter().run(args));
     }