fakefs/lib/fakefs.rb

module FakeFS
  module FileUtils
    extend self

    def mkdir_p(path)
      FileSystem.add(path, MockDir.new)
    end

    def rm(path)
      FileSystem.delete(path)
    end
    alias_method :rm_rf, :rm

    def ln_s(target, path)
      FileSystem.add(path, MockSymlink.new(target))
    end

    def cp_r(src, dest)
      if dir = FileSystem.find(src)
        FileSystem.add(dest, dir.entry)
      end
    end

    def mv(src, dest)
      if target = FileSystem.find(src)
        FileSystem.add(dest, target.entry)
        FileSystem.delete(src)
      end
    end
  end

  class File
    PATH_SEPARATOR = '/'

    def self.join(*parts)
      parts * PATH_SEPARATOR
    end

    def self.exists?(path)
      FileSystem.find(path)
    end

    def self.expand_path(path)
      ::File.expand_path(path)
    end

    def self.readlink(path)
      symlink = FileSystem.find(path)
      FileSystem.find(symlink.target).to_s
    end
  end

  class Dir
    def self.glob(pattern)
      FileSystem.find(pattern).map { |entry| entry.to_s}
    end

    def self.[](pattern)
      glob(pattern)
    end
  end

  module FileSystem
    extend self

    def fs
      @fs ||= MockDir.new('.')
    end

    def clear
      @fs = nil
    end

    def find(path)
      parts = path_parts(path)

      target = parts[0...-1].inject(fs) do |dir, part|
        dir[part] || {}
      end

      case parts.last
      when '*'
        target.values
      else
        target[parts.last]
      end
    end

    def add(path, object)
      parts = path_parts(path)

      d = parts[0...-1].inject(fs) do |dir, part|
        dir[part] ||= MockDir.new(part, dir)
      end

      object.name = parts.last
      object.parent = d
      d[parts.last] = object
    end

    def delete(path)
      if dir = FileSystem.find(path)
        dir.parent.delete(dir.name)
      end
    end

    def path_parts(path)
      path.split(File::PATH_SEPARATOR)
    end
  end

  class MockDir < Hash
    attr_accessor :name, :parent

    def initialize(name = nil, parent = nil)
      @name = name
      @parent = parent
    end

    def entry
      self
    end

    def to_s
      if parent && parent.to_s != '.'
        parent.to_s + '/' + name
      else
        name
      end
    end
  end

  class MockSymlink
    attr_accessor :name, :target
    alias_method  :to_s, :name

    def initialize(target)
      @target = target
    end

    def inspect
      "symlink(#{target.split('/').last})"
    end

    def entry
      FileSystem.find(target)
    end

    def method_missing(*args, &block)
      entry.send(*args, &block)
    end
  end
end

Object.class_eval do
  remove_const(:Dir)
  remove_const(:File)
  remove_const(:FileUtils)
end

File = FakeFS::File
FileUtils = FakeFS::FileUtils
Dir = FakeFS::Dir