Theory: Virtual file system

In this course, we'll create a virtual (not real) file system and implement everyday operations to work with it, such as calculating free space, searching for files and directories, etc. Let's create a file tree:

import { mkdir, mkfile } from '@hexlet/immutable-fs-trees';

// mkdir takes a list of children as its second parameter,
// which can either be directories created by mkdir,
// or files created by mkfile
const tree = mkdir('etc', [
  mkfile('bashrc'),
  mkdir('consul', [
    mkfile('config.json'),
  ]),
]);

The result is this structure:

etc
├── bashrc
└── consul
    └── config.json

By embedding mkdir and mkfile calls into other mkdir calls, any file structure can be obtained. The root of this structure will be the directory, and the leaves may contain both files and empty directories.

This structure is virtual, i.e., files and directories aren't created. All file system information stored in the tree variable. If you print it, you'll see the following:

{
  name: 'etc',
  type: 'directory',
  meta: {},
  children: [
    {
      name: 'bashrc',
      type: 'file',
      meta: {},
    },
    {
      name: 'consul',
      type: 'directory',
      meta: {},
      children: [
        {
          name: 'config.json',
          type: 'file',
          meta: {},
        }
      ],
    },
  ],
};

This is an internal implementation of the file tree. It consists of two types of nodes: directories and files.

Directory representation:

{
  name: /* ... */,
  type: 'directory',
  meta: {}, // Directory properties
  children: [/* ... */], // Here is where the children are kept
}

File representation:

{
  name: /* ... */,
  type: 'file',
  meta: {}, // File Properties
}

Files and directories have names, that's something they have in common. The type property defines the type of node and can be used to understand what is in front of us when processing this tree. meta is an object with arbitrary data, such as size, creation date and so on. Properties are set when the nodes are created:

mkfile('.bashrc', { size: 75 });
mkdir('hexlet', [/* children */], { owner: 'nobody' });

The metadata will be needed for functions that analyze the tree, such as those for calculating space usage.