fix(CoolMessages): prevent duplicate message add

Fixes a bug where any user could star react to a message and the bot
would unconditionally add that message to the cool messages board,
considering the fact that it would surpass the minimum reaction
count requirement.

This commit gets the bot to react with the same cool messages emoji the
first time and use that reaction as proof that it has quoted the message
and that it should not deal with it in case somebody reacts to it again.

application/src/main/java/org/togetherjava/tjbot/features/basic/CoolMessagesBoardManager.java

@@ -54,11 +54,18 @@ public void onMessageReactionAdd(MessageReactionAddEvent event) {
             return;
         }
 
+        // If the bot has already reacted to this message, then this means that
+        // the message has been quoted to the cool messages board, so skip it.
+        if (hasBotReacted(event.getJDA(), messageReaction)) {
+            return;
+        }
+
         if (isCoolEmoji && originalReactionsCount + 1 >= config.minimumReactions()) {
-            event.retrieveMessage()
-                .queue(message -> insertCoolMessage(boardChannel.orElseThrow(), message),
-                        e -> logger.warn("Tried to retrieve cool message but got: {}",
-                                e.getMessage()));
+            event.retrieveMessage().queue(message -> {
+                message.addReaction(REACT_EMOJI).queue();
+
+                insertCoolMessage(boardChannel.orElseThrow(), message);
+            }, e -> logger.warn("Tried to retrieve cool message but got: {}", e.getMessage()));
         }
     }
 
@@ -110,4 +117,13 @@ private static MessageEmbed createQuoteEmbed(Message message) {
             .setTimestamp(message.getTimeCreated())
             .build();
     }
+
+    /**
+     * Checks a {@link MessageReaction} to see if the bot has reacted to it.
+     */
+    private static boolean hasBotReacted(JDA jda, MessageReaction messageReaction) {
+        return messageReaction.retrieveUsers()
+            .parallelStream()
+            .anyMatch(user -> jda.getSelfUser().getIdLong() == user.getIdLong());
+    }
 }