KOProject/SimpleProtocol.java

package com.collibra.server;

import java.io.PrintWriter;

/**
 * A simple protocol for exchanging messages between a server and clients.
 *
 * @version 1.0
 * @author Yordan Kirov
 * @since 21/11/2018
 *
 */
class SimpleProtocol {
    /**
     * Sends a first message to every client that connects to the server.
     * @param out the PrintWriter with which the server sends messages to the client.
     * @param sessionId identification of the session with the current client.
     */
    public static void sendFirstMessage(PrintWriter out, String sessionId) {
        out.println("HI, I'M " + sessionId);
    }

    /**
     * Extracts and validates the name of the connected client from its first message.
     *
     * The server expects a message starting with "HI, I'M " and followed by the name of the client.
     * If the client doesn't fulfil the server expectations, by sending the wrong command or sending
     * a clientName that is non alphanumeric plus the character "-", the server is awaiting for the client to give a
     * proper name and doesn't accept other commands before that.
     *
     * @param out the PrintWriter with which the sever sends messages to the client.
     * @param message received from a client.
     *
     * @return clientName - the name of the client if it is valid, otherwise returns null;
     */
    public static String retrieveClientName(PrintWriter out, String message) {
        String clientName;
        if (message.contains("HI, I'M ")) {
            String unvalidatedClientName = message.replace("HI, I'M ", "");

            if (isValidName(unvalidatedClientName)) {
                clientName = unvalidatedClientName;
                System.out.println("Connected client: " + clientName);

                out.println("HI " + clientName);
                return clientName;
            }
        }

        out.println(unsupportedCommand());
        return null;
    }

    /**
     * Sends a message to the client before disconnecting.
     * The message includes the name of the client and the duration of the connection.
     *
     * @param out the PrintWriter with which the sever sends messages to the client.
     * @param clientName the name of the connected client.
     * @param startTime the time in milliseconds when the client connected.
     */
    public static void sendGoodbyeMessage(PrintWriter out, String clientName, long startTime) {
        if (out != null) {
            System.out.println("GOODBYE MESSAGE!" + clientName);
            long stopTime = System.currentTimeMillis();
            long duration = stopTime - startTime;
            out.println("BYE " + clientName + ", WE SPOKE FOR " + duration + " MS");
        }
    }

    /**
     * Adds a node (as a string) to the GRAPH.
     * When the name of the node is only including alphanumeric character,
     * plus the character "-" and the node doesn't already exist.
     *
     * @param message received from a client.
     * @return returns an error message if the node already exists
     * or success message if the node has been successfully added.
     */
    public static String addNode(String message) {
        String nodeName = message.replace("ADD NODE ", "");

        if (!isValidName(nodeName)) {
            return unsupportedCommand();
        }

        if (!Server.GRAPH.containsNode(nodeName)) {
            Server.GRAPH.addNode(nodeName);
            return "NODE ADDED";
        } else {
            return "ERROR: NODE ALREADY EXISTS";
        }
    }

    /**
     * Adds a directed edge to the GRAPH.
     * A directed edge has three parts, node from which it points, node to which it points
     * and weight which is a positive integer.
     * When the names of the nodes between the edge is are already existing and
     * the format of the command is valid and the weight is a positive integer.
     *
     * @param message received from a client.
     * @return returns an error message if the the edge can't be added
     *  or success message if the edge has been successfully added.
     */
    public static String addEdge(String message) {
        String edgeString = message.replace("ADD EDGE ", "");
        String[] edgeParts = edgeString.split(" ");

        if (!isValidEdge(edgeParts)) {
            return unsupportedCommand();
        }

        String fromName = edgeParts[0];
        String toName = edgeParts[1];

        if (Server.GRAPH.containsNode(fromName) && Server.GRAPH.containsNode(toName)) {
            int weight = Integer.valueOf(edgeParts[2]);

            Server.GRAPH.addEdge(fromName, toName, weight);
            return "EDGE ADDED";
        }

        return "ERROR: NODE NOT FOUND";
    }

    /**
     * Removes a node from the GRAPH, only when the node is already existing.
     * All edges that are linked to the removed node will also be removed.
     * @param message received from a client.
     * @return returns an error message if the node doesn't exist
     *  or success message if the node has been successfully removed.
     */
    public static String removeNode(String message) {
        String nodeName = message.replace("REMOVE NODE ", "");

        if (Server.GRAPH.containsNode(nodeName)) {
            Server.GRAPH.removeNode(nodeName);
            return "NODE REMOVED";
        } else {
            return "ERROR: NODE NOT FOUND";
        }
    }

    /**
     * Removes all directed edges from the GRAPH when the command is valid
     * and the both nodes that form the graph are existing.
     * @param message received from a client.
     * @return returns an error message if the command is invalid or the nodes between the graph aren't existing.
     * Returns a success message if the edges have been successfully removed.
     */
    public static String removeEdge(String message) {
        String edgeString = message.replace("REMOVE EDGE ", "");
        String[] edgeParts = edgeString.split(" ");

        if (edgeParts.length != 2) {
            return unsupportedCommand();
        }

        String fromName = edgeParts[0];
        String toName = edgeParts[1];

        if (Server.GRAPH.containsNode(fromName) && Server.GRAPH.containsNode(toName)) {
            Server.GRAPH.removeEdge(fromName, toName);
            return "EDGE REMOVED";
        }

        return "ERROR: NODE NOT FOUND";
    }

    /**
     * Calculates the sum of the weights of the shortest path between two nodes in the GRAPH,
     * when the input of the command is valid and the nodes exist in the GRAPH.
     * @param message received from a client.
     * @return the sum of the weights of the shortest path between two nodes.
     * Returns an error message if the command is invalid or the nodes of the GRAPH aren't existing.
     */
    public static String getShortestPath(String message) {
        String fromAndTo = message.replace("SHORTEST PATH ", "");
        String[] fromTo = fromAndTo.split(" ");
        if (fromTo.length != 2) {
            return unsupportedCommand();
        }

        String from = fromTo[0];
        String to = fromTo[1];

        if (Server.GRAPH.containsNode(from) && Server.GRAPH.containsNode(to)) {
            return String.valueOf(Server.GRAPH.getShortestPathDistance(from, to));
        }

        return "ERROR: NODE NOT FOUND";
    }

    /**
     * Finds all the nodes that are closer to a node from the client message than the given weight.
     *
     * For example:
     * Simple graph: Mark -­ 5 -­> Michael -­ 2 -­> Madeleine -­ 8 -­> Mufasa
     * CLOSER THAN 8 Mark
     * Would return: Madeleine,Michael
     * Because Michael is at weight 5 from Mark and Madeleine is at weight 7 (5+2) from Mark.
     *
     * @param message received from a client.
     * @return a comma separated list(no spaces) of found nodes, that are closer to a node from the client message,
     * sorted alphabetically by name, not including the starting node.
     * Returns an error message if the command is invalid or the node of the GRAPH isn't existing.
     */
    public static String getCloserThan(String message) {
        String weightAndNode = message.replace("CLOSER THAN ", "");
        String[] weightNode = weightAndNode.split(" ");

        if (weightNode.length != 2 || !isValidWeightString(weightNode[0])) {
            return unsupportedCommand();
        }
        int weight = Integer.valueOf(weightNode[0]);
        String nodeName = weightNode[1];

        if (Server.GRAPH.containsNode(nodeName)) {
            String path = Server.GRAPH.getNodesCloserThan(weight, nodeName);
            return path;
        }

        return "ERROR: NODE NOT FOUND";
    }

    /**
     * Returns string for unsupported command.
     * @return string for unsupported command.
     */
    public static String unsupportedCommand() {
        return "SORRY, I DIDN'T UNDERSTAND THAT";
    }


    private static boolean isValidEdge(String[] input) {
        if (input.length != 3) {
            return false;
        }

        String weightString = input[2];

        boolean isValidWeightString = isValidWeightString(weightString);

        return isValidWeightString;
    }

    private static boolean isValidWeightString(String weightString) {
        return weightString.length() > 0 &&
                weightString.chars().allMatch(Character::isDigit);
    }

    private static boolean isValidName(String input) {
        return input.matches("[A-Za-z0-9-]+");
    }
}