[Bleeding] Added Conversations API. Addresses BUKKIT-864

By: rmichela <deltahat@gmail.com>

paper-server/src/main/java/org/bukkit/craftbukkit/conversations/ConversationTracker.java

@@ -0,0 +1,62 @@
+package org.bukkit.craftbukkit.conversations;
+
+import org.bukkit.conversations.Conversation;
+
+import java.util.Deque;
+import java.util.LinkedList;
+
+/**
+ */
+public class ConversationTracker {
+
+    private Deque<Conversation> conversationQueue = new LinkedList<Conversation>();
+
+    public synchronized boolean beginConversation(Conversation conversation) {
+        if (!conversationQueue.contains(conversation)) {
+            conversationQueue.addLast(conversation);
+            if (conversationQueue.getFirst() == conversation) {
+                conversation.begin();
+                conversation.outputNextPrompt();
+                return true;
+            }
+        }
+        return true;
+    }
+
+    public synchronized void abandonConversation(Conversation conversation) {
+        if (!conversationQueue.isEmpty()) {
+            if (conversationQueue.getFirst() == conversation) {
+                conversation.abandon();
+            }
+            if (conversationQueue.contains(conversation)) {
+                conversationQueue.remove(conversation);
+            }
+            if (!conversationQueue.isEmpty()) {
+                conversationQueue.getFirst().outputNextPrompt();
+            }
+        }
+    }
+
+    public synchronized void abandonAllConversations() {
+
+        Deque<Conversation> oldQueue = conversationQueue;
+        conversationQueue = new LinkedList<Conversation>();
+        for(Conversation conversation : oldQueue) {
+            conversation.abandon();
+        }
+    }
+
+    public synchronized void acceptConversationInput(String input) {
+        if (isConversing()) {
+            conversationQueue.getFirst().acceptInput(input);
+        }
+    }
+
+    public synchronized boolean isConversing() {
+        return !conversationQueue.isEmpty();
+    }
+
+    public synchronized boolean isConversingModaly() {
+        return isConversing() && conversationQueue.getFirst().isModal();
+    }
+}