package algorithm.loadbalance;

import com.alibaba.fastjson.JSON;

import java.util.*;

/**
 * @author Cao Xuan
 * @date 2021/3/21 20:04
 * @update 2021/5/5
 */
public class LoadBalanceDemo {

    private final List<Server> serverList = new ArrayList<>();

    /**
     * client -> server
     */
    private final Map<Client, Server> clientServerMap = new HashMap<>();
    
    /**
     * <---head---tail--->
     * <---light---weight--->
     * <---former---latter-->
     */
    @Deprecated
    private void sort() {
        for (int i = serverList.size() - 1; i > 0; i--) {
            for (int j = i - 1; j > -1; j--) {
                Server latter = new Server(serverList.get(i));
                Server former = new Server(serverList.get(j));
                if (latter.getCurrentLoad().size() > former.getCurrentLoad().size()) {
                    serverList.set(i, former);
                    serverList.set(j, latter);
                }
            }
        }
        System.out.println("sorting...");
    }

    /**
     * <---head---tail--->
     * <---light---weight--->
     * <---former---latter-->
     */
    private void leafShift() {
        int size = serverList.size();
        for (int i = size - 2; i >= 0; i--) {
            Server latter = new Server(serverList.get(size - 1));
            Server former = new Server(serverList.get(i));
            if (latter.getCurrentLoad().size() > former.getCurrentLoad().size()) {
                serverList.set(size - 1, former);
                serverList.set(i, latter);
                System.out.println("leaf shift");
            }
        }
    }

    private void rightShift(int index) {
        int size = serverList.size();
        for (int i = index + 1; i < size; i++) {
            Server former = new Server(serverList.get(index));
            Server latter = new Server(serverList.get(i));
            if (former.getCurrentLoad().size() < latter.getCurrentLoad().size()) {
                serverList.set(i, former);
                serverList.set(index, latter);
                System.out.println("right shift");
            }
        }
    }
    
    public Server addClient(Client client) {
        if (serverList.size() > 0) {
            Server server = new Server(serverList.get(serverList.size() - 1));
            String serverName = server.getName();
            serverList.get(serverList.size() - 1).updateCurrentLoad(client);
            System.out.println("Hi,[" + client.getUsername() + "]. Assign [" + serverName + "] to you");
            leafShift();
            show();
            return server;
        } else {
            System.err.println("no server");
            return null;
        }
    }

    public void removeClient(String clientName) {
        Server server = clientServerMap.get(new Client(clientName));
        int index = serverList.indexOf(server);
        if (-1 != index) {
            server.currentLoad.remove(new Client(clientName));
            rightShift(index);
            System.out.println("remove a client [" + clientName + "]");
        } else {
            System.err.println("index = -1");
        }

        show();
    }

    public void addServer(String name) {
        Server server = new Server(name, new HashSet<>());
        if (serverList.contains(server)) {
            System.err.println("The server [" + name + "] already exists");
            show();
            return;
        }
        serverList.add(server);
        System.out.println("add a server [" + name + "]");
        show();
    }

    public void removeServer(String serverName) {
        serverList.remove(new Server(serverName));
        System.out.println("add a server [" + serverName + "]");
        show();
    }

    private static class Client {

        private String username;

        public Client(String username) {
            this.username = username;
        }

        public String getUsername() {
            return username;
        }

        public void setUsername(String username) {
            this.username = username;
        }

        @Override
        public boolean equals(Object obj) {
            if (!(obj instanceof Client)) {
                return false;
            }
            Client client = (Client) obj;
            return this.getUsername().equals(client.getUsername());
        }

        @Override
        public int hashCode() {
            return Objects.hash(username);
        }

        @Override
        public String toString() {
            return JSON.toJSONString(this);
        }
    }

    private static class Server {

        private String name;
        
        private Set<Client> currentLoad;

        public Server(String name) {
            this.name = name;
        }

        public Server(Server server) {
            this.name = server.name;
            this.currentLoad = server.currentLoad;
        }

        public Server(String name, Set<Client> currentLoad) {
            this.name = name;
            this.currentLoad = currentLoad;
        }

        public String getName() {
            return name;
        }

        public void setName(String name) {
            this.name = name;
        }

        public Set<Client> getCurrentLoad() {
            return currentLoad;
        }

        public void setCurrentLoad(Set<Client> currentLoad) {
            this.currentLoad = currentLoad;
        }

        public void updateCurrentLoad(Client client) {
            this.currentLoad.add(client);
        }

        @Override
        public boolean equals(Object obj) {
            if (!(obj instanceof Server)) {
                return false;
            }
            Server server = (Server) obj;
            return this.getName().equals(server.getName());
        }

        @Override
        public String toString() {
            return JSON.toJSONString(this);
        }
    }

    public static void main(String[] args) {

        LoadBalanceDemo loadBalanceDemo = new LoadBalanceDemo();

        System.out.println("---------------USAGE--------------");
        System.out.println("Add a server: [s+${serverName}]");
        System.out.println("Add a client: [c+${clientName}]");
        System.out.println("Remove a server: [s-${serverName}]");
        System.out.println("Remove a client: [c-${clientName}]");
        System.out.println("Show Current Load: [show]");
        System.out.println("---------------USAGE--------------");

        while (true) {
            System.out.println("ready");
            System.out.println();
            Scanner scanner = new Scanner(System.in);
            String s = scanner.next();
            if ("show".equals(s)) {
                loadBalanceDemo.show();
            } else if (s.startsWith("c+")) {
                String clientName = s.substring(2);
                Client client = new Client(clientName);
                Server server = loadBalanceDemo.addClient(client);
                loadBalanceDemo.clientServerMap.put(client, server);
            } else if (s.startsWith("s+")) {
                String serverName = s.substring(2);
                loadBalanceDemo.addServer(serverName);
            } else if (s.startsWith("c-")) {
                String clientName = s.substring(2);
                loadBalanceDemo.removeClient(clientName);
            } else if (s.startsWith("s-")) {
                String serverName = s.substring(2);
                loadBalanceDemo.removeServer(serverName);
            } else {
                System.out.println("?");
            }
            System.out.println("----------------------------------");
        }
    }

    private void show() {
        System.out.println("current load " + serverList);
    }
}