require 'set'

module Jekyll
  # Handles the cleanup of a site's destination before it is built.
  class Cleaner
    HIDDEN_FILE_REGEX = /\/\.{1,2}$/
    attr_reader :site

    def initialize(site)
      @site = site
    end

    # Cleans up the site's destination directory
    def cleanup!
      FileUtils.rm_rf(obsolete_files)
      FileUtils.rm_rf(metadata_file) unless @site.incremental?
    end

    private

    # Private: The list of files and directories to be deleted during cleanup process
    #
    # Returns an Array of the file and directory paths
    def obsolete_files
      (existing_files - new_files - new_dirs + replaced_files).to_a
    end

    # Private: The metadata file storing dependency tree and build history
    #
    # Returns an Array with the metdata file as the only item
    def metadata_file
      [site.regenerator.metadata_file]
    end

    # Private: The list of existing files, apart from those included in keep_files and hidden files.
    #
    # Returns a Set with the file paths
    def existing_files
      files = Set.new
      regex = keep_file_regex
      dirs = keep_dirs

      Utils.safe_glob(site.in_dest_dir, ["**", "*"], File::FNM_DOTMATCH).each do |file|
        next if file =~ HIDDEN_FILE_REGEX || file =~ regex || dirs.include?(file)
        files << file
      end

      files
    end

    # Private: The list of files to be created when site is built.
    #
    # Returns a Set with the file paths
    def new_files
      files = Set.new
      site.each_site_file { |item| files << item.destination(site.dest) }
      files
    end

    # Private: The list of directories to be created when site is built.
    # These are the parent directories of the files in #new_files.
    #
    # Returns a Set with the directory paths
    def new_dirs
      new_files.map { |file| parent_dirs(file) }.flatten.to_set
    end

    # Private: The list of parent directories of a given file
    #
    # Returns an Array with the directory paths
    def parent_dirs(file)
      parent_dir = File.dirname(file)
      if parent_dir == site.dest
        []
      else
        [parent_dir] + parent_dirs(parent_dir)
      end
    end

    # Private: The list of existing files that will be replaced by a directory during build
    #
    # Returns a Set with the file paths
    def replaced_files
      new_dirs.select { |dir| File.file?(dir) }.to_set
    end

    # Private: The list of directories that need to be kept because they are parent directories
    # of files specified in keep_files
    #
    # Returns a Set with the directory paths
    def keep_dirs
      site.keep_files.map { |file| parent_dirs(site.in_dest_dir(file)) }.flatten.to_set
    end

    # Private: Creates a regular expression from the config's keep_files array
    #
    # Examples
    #   ['.git','.svn'] creates the following regex: /\/(\.git|\/.svn)/
    #
    # Returns the regular expression
    def keep_file_regex
      Regexp.union(site.keep_files)
    end
  end
end
