Refactor code to include packages and more OOP

Author: nzixuan

README.md

@@ -1,4 +1,4 @@
-# Duke project template
+# duke.Duke project template
 
 This is a project template for a greenfield Java project. It's named after the Java mascot _Duke_. Given below are instructions on how to use it.
 
@@ -13,7 +13,7 @@ Prerequisites: JDK 11, update Intellij to the most recent version.
    1. If there are any further prompts, accept the defaults.
 1. Configure the project to use **JDK 11** (not other versions) as explained in [here](https://www.jetbrains.com/help/idea/sdk.html#set-up-jdk).<br>
    In the same dialog, set the **Project language level** field to the `SDK default` option.
-3. After that, locate the `src/main/java/Duke.java` file, right-click it, and choose `Run Duke.main()` (if the code editor is showing compile errors, try restarting the IDE). If the setup is correct, you should see something like the below as the output:
+3. After that, locate the `src/main/java/duke.Duke.java` file, right-click it, and choose `Run duke.Duke.main()` (if the code editor is showing compile errors, try restarting the IDE). If the setup is correct, you should see something like the below as the output:
    ```
    Hello from
     ____        _        

src/main/java/Duke.java

@@ -1,16 +0,0 @@
-import java.util.Scanner;
-
-public class Main {
-    public static void main(String[] args) {
-        Duke duke = new Duke();
-        duke.loadFile();
-        duke.greet();
-        boolean loop = true;
-        Scanner scanner = new Scanner(System.in);  // Create a Scanner object
-        while(loop) {
-            String input = scanner.nextLine();
-            loop = duke.process(input);
-        }
-
-    }
-}

src/main/java/Main.java

@@ -0,0 +1,43 @@
+package duke;
+
+import duke.command.Command;
+import java.util.Scanner;
+
+public class Duke {
+
+    private Storage storage;
+    private TaskList tasks;
+    private Ui ui;
+
+    public Duke(String filePath) {
+        ui = new Ui();
+        storage = new Storage(filePath);
+        try {
+            tasks = new TaskList(storage.load(), storage);
+        } catch (DukeException e) {
+            ui.showLoadingError();
+            tasks = new TaskList(storage);
+        }
+    }
+
+    public void run() {
+        ui.greet();
+        boolean isExit = false;
+        Scanner scanner = new Scanner(System.in);  // Create a Scanner object
+        while (!isExit) {
+            String input = scanner.nextLine();
+            try {
+                Command c = Parser.parse(input);
+                c.execute(tasks, ui, storage);
+                isExit = c.isExit();
+            } catch (DukeException e) {
+                ui.printError(e.getMessage());
+            }
+        }
+    }
+
+    public static void main(String[] args) {
+        new Duke("data/tasks.txt").run();
+    }
+
+}

src/main/java/duke/Duke.java

@@ -0,0 +1,7 @@
+package duke;
+
+public class DukeException extends Exception {
+        public DukeException(String errorMessage) {
+            super(errorMessage);
+        }
+}