import java.util.Scanner;

/**
 * Builds a decision tree by playing a guessing game with a human.
 */
public class GuessingGame {

    /**
     * Utility method: read a line from the user and return whether
     * it was a "yes" (versus a "no")
     */
    private static boolean answeredYes(Scanner human) {
 
        do {
            String response = human.nextLine().toLowerCase();
            if (response.equals("yes")) {
                return true;
            } else if (response.equals("no")) {
                return false;
            } else {
                System.out.println("Answer yes or no: ");
            }
        } while (true); // loop until yes or no is given
    }

    /**
     * Make a decision (if at a leaf) or ask a question (if at an interior node)
     * using the given decision tree.
     */
    public static void play(Scanner human, BinaryTree<String> tree) {
        if (tree.isLeaf()) {

            // at leaf - must be single object left
            System.out.println("Is it a " + tree.value() + "?");
            if (answeredYes(human)) {
                System.out.println("I'm so smart!");
            } else {
                learn(human, tree);
            }

        } else {

            // further choices; must ask a question to distinguish them
            String nextQuestion = tree.value();
            System.out.println(nextQuestion);
            if (answeredYes(human)) {
                play(human, tree.left());
            } else {
                play(human, tree.right());
            }

        }
    }

    /**
     * Respond to a wrong answer by updating the decision tree with new knowledge.
     */
    public static void learn(Scanner human, BinaryTree<String> leaf) {
        System.out.println("Darn. What were you thinking of?");
        BinaryTree<String> newObject = new BinaryTree<String>(human.nextLine());
        BinaryTree<String> oldObject = new BinaryTree<String>(leaf.value());

        System.out.println("What yes/no question would distinguish a " +
            newObject.value() + " (yes) from a " + oldObject.value() + " (no)?");

        String newQuestion = human.nextLine();
        leaf.setValue(newQuestion);
        leaf.setLeft(newObject); // note: no longer a leaf
        leaf.setRight(oldObject);
    }

    /**
     * Initialize a new decision tree and play the guessing game.
     */
    public static void main(String args[]) {
        Scanner human = new Scanner(System.in);

        BinaryTree<String> tree = new BinaryTree<String>("computer");

        do {
            System.out.println("\n===================================");
            System.out.println("Think of something...I'll guess it!");
            System.out.println("Press enter when you're ready.");
            human.nextLine(); // wait for enter
            play(human, tree);
        } while (true);
    }
}