Add TreeCommand to display directory structure

Closes #13

Author: nihaltp

src/main/java/com/mycmd/App.java

@@ -56,6 +56,7 @@ private static void registerCommands(Map<String, Command> commands) {
         commands.put("whoami", new WhoamiCommand());
         commands.put("touch", new TouchCommand());
         commands.put("time", new TimeCommand());
+        commands.put("tree", new TreeCommand());
         commands.put("date", new DateCommand());
     }
 }

src/main/java/com/mycmd/commands/TreeCommand.java

@@ -0,0 +1,37 @@
+package com.mycmd.commands;
+
+import com.mycmd.Command;
+import com.mycmd.ShellContext;
+import java.io.File;
+
+public class TreeCommand implements Command{
+    public void execute(String[] args, ShellContext context){
+        File[] files = context.getCurrentDir().listFiles();
+
+        if (files == null || files.length == 0) {
+            System.out.println("No files found.");
+            return;
+        }
+
+        System.out.println(context.getCurrentDir().getAbsolutePath());
+        printDirectory(files, "", true);
+        System.out.println();
+    }
+
+    private void printDirectory(File[] files, String prefix, boolean isLast) {
+        if (files == null || files.length == 0) return;
+
+        for (int i = 0; i < files.length; i++) {
+            File f = files[i];
+            if (f.isHidden()) continue;
+
+            boolean last = (i == files.length - 1);
+            System.out.println(prefix + (last ? "└───" : "├───") + f.getName());
+
+            if (f.isDirectory()) {
+                String newPrefix = prefix + (last ? "    " : "│   ");
+                printDirectory(f.listFiles(), newPrefix, last);
+            }
+        }
+    }
+}