Unix File System

class FileNode {
  constructor(type) {
    this.type = type
    this.children = {}
  }
}

class FileSystem {
  constructor() {
    this.root = new FileNode('dir') // Root directory
    this.currentPath = this.root;
    this.pathStack = ['/']; // Keeps track of current path
  }

  // Helper function to traverse the directory tree
  #traverse(path) {
    const parts = path.split('/').filter(Boolean);
    let node = this.root;

    for (const part of parts) {
      if (!node.children[part] || node.children[part].type !== 'dir') {
        throw new Error(`Directory '${part}' does not exist`);
      }
      node = node.children[part];
    }
    return node;
  }

  // Create a directory
  mkdir(path) {
    const parts = path.split('/').filter(Boolean);
    let node = this.root;

    for (const part of parts) {
      if (!node.children[part]) {
        node.children[part] = new FileNode('dir');
      }
      node = node.children[part];

      if (node.type !== 'dir') {
        throw new Error(`${part} is a file, cannot create directory here`);
      }
    }
  }

  // Create a file
  touch(path) {
    const parts = path.split('/').filter(Boolean);
    const fileName = parts.pop();
    let node = this.root;

    for (const part of parts) {
      if (!node.children[part] || node.children[part].type !== 'dir') {
        throw new Error(`Directory '${part}' does not exist`);
      }
      node = node.children[part];
    }

    node.children[fileName] = new FileNode('file')
  }

  // List contents of a directory
  ls(path = '') {
    const node = path ? this.#traverse(path) : this.currentPath;

    if (node.type !== 'dir') {
      throw new Error(`${path} is not a directory`);
    }

    return Object.keys(node.children);
  }

  // Change directory
  cd(path) {
    if (path === '/') {
      this.currentPath = this.root;
      this.pathStack = ['/'];
      return;
    }

    const node = this.#traverse(path);
    this.currentPath = node;
    this.pathStack = path.split('/').filter(Boolean);
  }

  // Print working directory
  pwd() {
    return '/' + this.pathStack.join('/');
  }
}

// Example Usage:
const fs = new FileSystem();

fs.mkdir('/home/user/documents');
fs.mkdir('/home/user/photos');
fs.touch('/home/user/documents/resume.pdf');
fs.touch('/home/user/photos/selfie.png');

console.log(fs.ls('/home/user'));  // ['documents', 'photos']
console.log(fs.ls('/home/user/documents'));  // ['resume.pdf']

fs.cd('/home/user/documents');
console.log(fs.pwd());  // '/home/user/documents'

fs.cd('/');
console.log(fs.pwd());  // '/'

/* 
[ 'documents', 'photos' ]
[ 'resume.pdf' ]
/home/user/documents
//
*/