[Bleeding] Added Conversations API. Addresses BUKKIT-864

By: rmichela <deltahat@gmail.com>

paper-api/src/main/java/org/bukkit/conversations/ValidatingPrompt.java

@@ -0,0 +1,69 @@
+package org.bukkit.conversations;
+
+import org.bukkit.ChatColor;
+
+/**
+ * ValidatingPrompt is the base class for any prompt that requires validation. ValidatingPrompt will keep replaying
+ * the prompt text until the user enters a valid response.
+ */
+public abstract class ValidatingPrompt implements Prompt {
+    public ValidatingPrompt() {
+        super();
+    }
+
+    /**
+     * Accepts and processes input from the user and validates it. If validation fails, this prompt is returned for
+     * re-execution, otherwise the next Prompt in the prompt graph is returned.
+     * @param context Context information about the conversation.
+     * @param input The input text from the user.
+     * @return This prompt or the next Prompt in the prompt graph.
+     */
+    public Prompt acceptInput(ConversationContext context, String input) {
+        if (isInputValid(context, input)) {
+            return acceptValidatedInput(context, input);
+        } else {
+            String failPrompt = getFailedValidationText(context, input);
+            if (failPrompt != null) {
+                context.getForWhom().sendRawMessage(ChatColor.RED + failPrompt);
+            }
+            // Redisplay this prompt to the user to re-collect input
+            return this;
+        }
+    }
+
+    /**
+     * Ensures that the prompt waits for the user to provide input.
+     * @param context Context information about the conversation.
+     * @return True.
+     */
+    public boolean blocksForInput(ConversationContext context) {
+        return true;
+    }
+
+    /**
+     * Override this method to check the validity of the player's input.
+     * @param context Context information about the conversation.
+     * @param input The player's raw console input.
+     * @return True or false depending on the validity of the input.
+     */
+    protected abstract boolean isInputValid(ConversationContext context, String input);
+
+    /**
+     * Override this method to accept and processes the validated input from the user. Using the input, the next Prompt
+     * in the prompt graph should be returned.
+     * @param context Context information about the conversation.
+     * @param input The validated input text from the user.
+     * @return The next Prompt in the prompt graph.
+     */
+    protected abstract Prompt acceptValidatedInput(ConversationContext context, String input);
+
+    /**
+     * Optionally override this method to display an additional message if the user enters an invalid input.
+     * @param context Context information about the conversation.
+     * @param invalidInput The invalid input provided by the user.
+     * @return A message explaining how to correct the input.
+     */
+    protected String getFailedValidationText(ConversationContext context, String invalidInput) {
+        return null;
+    }
+}