feat: add singleton class as database in app

Author: HK-Transfield

src/main/java/com/hktransfield/App.java

@@ -1,7 +1,51 @@
 package com.hktransfield;
 
+import java.util.Scanner;
+import com.hktransfield.menus.*;
+
 public class App {
+
+    /**
+     * Main method. It is the entry point into the program
+     *
+     * @param args
+     */
     public static void main(String[] args) {
-        AuthenticationSystem.startupMenu();
+        int option = 0;
+        Scanner s = new Scanner(System.in);
+        boolean keepRunning = true;
+        UserDatabase udb = UserDatabase.getInstance();
+
+        Home.openMenu();
+
+        while(keepRunning) {
+            try {
+                option = s.nextInt();
+                switch (option) {
+                    case 1: // Sign in
+                        Login.openMenu(udb);
+                        break;
+                    case 2: // Registration
+                    Registration.openMenu(udb);
+                    break;
+                    case 3: // Exit the application
+                        PrintUtils.print("Goodbye!");
+                        keepRunning = false;
+                        break;
+                        default:
+                        System.out.println();
+                        PrintUtils.println("Please enter a valid option! (1/2/3)");
+                        break;
+                    }
+
+                    if(!keepRunning) break;
+                    else Home.openMenu();
+            } catch (Exception e) {
+                PrintUtils.println(PrintUtils.ANSI_RED + "Something unexpected happened:" + PrintUtils.ANSI_RESET);
+                System.err.println(e);
+            }
+        }
+
+        s.close();
     }
 }

src/main/java/com/hktransfield/UserDatabase.java

@@ -0,0 +1,69 @@
+package com.hktransfield;
+import java.util.HashMap;
+import java.util.Map;
+
+import com.password4j.Hash;
+import com.password4j.Password;
+
+/** Represents
+ * https://happycoding.io/tutorials/java-server/secure-password-storage
+ * https://www.quickprogrammingtips.com/java/how-to-securely-store-passwords-in-java.html
+ */
+public class UserDatabase {
+	// declare class scope variables
+    private static UserDatabase instance;
+    private Map<String, Hash> userDB = new HashMap<>();
+	private UserDatabase(){} // singleton class
+
+	/**
+	 * Create UserDatabase object if it does not exist.
+	 *
+	 * @return
+	 */
+    public static UserDatabase getInstance(){
+		if(instance == null) instance = new UserDatabase();
+        return instance;
+	}
+
+	/**
+	 * Prevents a new user from creating an account with an
+	 * already existing username.
+	 *
+	 * @param username the chosen username to validate
+	 * @return true if username already exists
+	 */
+    public boolean isUsernameTaken(String username){
+		return userDB.containsKey(username);
+	}
+
+	/**
+	 *
+	 * @param username
+	 * @param password
+	 */
+	public void registerUser(String username, char[] password){
+		Hash hash = Password.hash(new String(password)).addRandomSalt(42).addPepper("COMPX518").withArgon2();
+		userDB.put(username, hash);
+	}
+
+	/**
+	 *
+	 * @param username
+	 * @param password
+	 * @return
+	 */
+	public boolean isLoginCorrect(String username, char[] password) {
+
+		// username isn't registered
+		if(!userDB.containsKey(username)){
+			System.out.println("Can't find username");
+			return false;
+		}
+
+		Hash storedPassword = userDB.get(username);
+		boolean verified = Password.check(new String(password), storedPassword);
+
+		return verified;
+	}
+
+}