module FakeFS
  # FileSystem module
  module FileSystem
    extend self

    def dir_levels
      @dir_levels ||= ['/']
    end

    def fs
      @fs ||= FakeDir.new('/')
    end

    def clear
      @dir_levels = nil
      @fs = nil
    end

    def files
      fs.entries
    end

    # Finds files/directories using the exact path, without expanding globs.
    def find(path, dir: nil)
      parts = path_parts(normalize_path(path, dir: dir))
      return fs if parts.empty? # '/'

      find_recurser(fs, parts)
    end

    # Finds files/directories expanding globs.
    def find_with_glob(path, find_flags = 0, gave_char_class = false, dir: nil)
      parts = path_parts(normalize_path(path, dir: dir))
      return fs if parts.empty? # '/'

      entries = Globber.expand(path).flat_map do |pattern|
        parts = path_parts(normalize_path(pattern, dir: dir))
        find_with_glob_recurser(fs, parts, find_flags, gave_char_class).flatten
      end

      case entries.length
      when 0 then nil
      when 1 then entries.first
      else entries
      end
    end

    def add(path, object = FakeDir.new)
      parts = path_parts(normalize_path(path))

      d = parts[0...-1].reduce(fs) do |dir, part|
        assert_dir dir[part] if dir[part]
        dir[part] ||= FakeDir.new(part, dir)
      end

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

    # copies directories and files from the real filesystem
    # into our fake one
    def clone(path, target = nil)
      path    = RealFile.expand_path(path)
      pattern = File.join(path, '**', '*')
      files   = if RealFile.file?(path)
                  [path]
                else
                  [path] + RealDir.glob(pattern, RealFile::FNM_DOTMATCH)
                end

      files.each do |f|
        target_path = target ? f.gsub(path, target) : f

        if RealFile.symlink?(f)
          FileUtils.ln_s(RealFile.readlink(f), f)
        elsif RealFile.file?(f)
          FileUtils.mkdir_p(File.dirname(f))
          File.open(target_path, File::WRITE_ONLY) do |g|
            g.print RealFile.read(f)
          end
        elsif RealFile.directory?(f)
          FileUtils.mkdir_p(target_path)
        end
      end
    end

    def delete(path)
      return unless (node = FileSystem.find(path))
      node.delete
      true
    end

    def chdir(dir, &blk)
      new_dir = find(dir)
      dir_levels.push dir.to_s if blk

      raise Errno::ENOENT, dir.to_s unless new_dir
      raise Errno::ENOTDIR, dir.to_s unless File.directory? new_dir

      dir_levels.push dir.to_s unless blk
      yield(dir) if blk
    ensure
      dir_levels.pop if blk
    end

    def path_parts(path)
      Globber.path_components(path)
    end

    def normalize_path(path, dir: nil)
      if Pathname.new(path).absolute?
        RealFile.expand_path(path)
      else
        dir ||= dir_levels
        dir = Array(dir)
        parts = dir + [path]
        RealFile.expand_path(parts.reduce do |base, part|
                               Pathname(base) + part
                             end.to_s)
      end
    end

    def current_dir
      find('.')
    end

    private

    def find_recurser(dir, parts, find_flags = 0, gave_char_class = false)
      return nil unless dir.respond_to? :[]
      head, *parts = parts
      match = dir.entries.find { |e| e.name == head }

      if parts.empty? # we're done recursing
        match
      else
        find_recurser(match, parts, find_flags, gave_char_class)
      end
    end

    def find_with_glob_recurser(dir, parts, find_flags = 0, gave_char_class = false)
      return [] unless dir.respond_to? :[]
      pattern, *parts = parts
      matches =
        case pattern
        when '**'
          case parts
          when ['*']
            parts = [] # end recursion
            directories_under(dir).map do |d|
              d.entries.select do |f|
                (f.is_a?(FakeFile) || f.is_a?(FakeDir)) &&
                  f.name.match(/\A(?!\.)/)
              end
            end.flatten.uniq
          when []
            parts = [] # end recursion
            dir.entries.flatten.uniq
          else
            directories_under(dir)
          end
        else
          Globber.expand(pattern).flat_map do |subpattern|
            dir.matches(Globber.regexp(subpattern, find_flags, gave_char_class))
          end
        end

      if parts.empty? # we're done recursing
        matches
      else
        matches.map { |entry| find_with_glob_recurser(entry, parts, find_flags, gave_char_class) }
      end
    end

    def directories_under(dir)
      children = dir.entries.select { |f| f.is_a? FakeDir }
      ([dir] + children + children.map { |c| directories_under(c) })
        .flatten.uniq
    end

    def assert_dir(dir)
      raise Errno::EEXIST, dir.name unless dir.is_a?(FakeDir)
    end
  end
end
