module AssetHat
  class << self
    attr_accessor :last_commit_ids, :last_bundle_commit_ids #:nodoc:
  end

  # Usage:
  #
  #     AssetHat.last_commit_id('public/stylesheets/application.css')
  #     AssetHat.last_commit_id('public/stylesheets/ie.css',
  #                             'public/stylesheets/ie7.css',
  #                             'public/stylesheets/ie6.css')
  #
  # Returns a string of the commit ID for the file with the most recent
  # commit. If the file(s) cannot be found, `nil` is returned. Options:
  #
  # [vcs] Version control system. Currently, the only supported value is
  #       <code>:git</code>.
  def self.last_commit_id(*args)
    # Process arguments
    options = args.extract_options!
    options = options.symbolize_keys.reverse_merge(:vcs => :git)
    filepaths = args.join(' ')

    # Validate options
    if options[:vcs] != :git
      raise 'Git is currently the only supported VCS.' and return
    end

    @last_commit_ids ||= {}
    if @last_commit_ids[filepaths].blank?
      h = `git log -1 --pretty=format:%h #{filepaths} 2>/dev/null`
        # `h` has either the abbreviated Git commit hash or an empty string
      @last_commit_ids[filepaths] = h if h.present?
    end
    @last_commit_ids[filepaths]
  end

  # Usage:
  #
  #     AssetHat.last_bundle_commit_id('application', :css)
  #
  # Returns a string of the latest commit ID for the given bundle, based
  # on which of its files were most recently modified in the repository. If
  # no ID can be found, `nil` is returned.
  def self.last_bundle_commit_id(bundle, type)
    # Process arguments
    type = type.to_sym
    unless TYPES.include?(type)
      raise %{Unknown type "#{type}"; should be one of: #{TYPES.join(', ')}.}
      return
    end

    # Default to `{:css => {}, :js => {}}`
    @last_bundle_commit_ids ||=
      TYPES.inject({}) { |hsh, t| hsh.merge(t => {}) }

    if @last_bundle_commit_ids[type][bundle].blank?
      dir = self.assets_dir(type)
      filepaths = self.bundle_filepaths(bundle, type)
      if filepaths.present?
        @last_bundle_commit_ids[type][bundle] =
          self.last_commit_id(*filepaths)
      end
    end

    @last_bundle_commit_ids[type][bundle]
  end

  def self.last_commit_ids #:nodoc:
    @last_commit_ids
  end

  # Precomputes and caches the last commit ID for all bundles. Your web server
  # process(es) should run this at boot to avoid overhead during user runtime.
  def self.cache_last_commit_ids
    AssetHat::TYPES.each do |type|
      next if AssetHat.config[type.to_s].blank? ||
              AssetHat.config[type.to_s]['bundles'].blank?

      AssetHat.config[type.to_s]['bundles'].keys.each do |bundle|
        # Memoize commit ID for this bundle
        AssetHat.last_bundle_commit_id(bundle, type) if AssetHat.cache?

        # Memoize commit IDs for each file in this bundle
        AssetHat.bundle_filepaths(bundle, type).each do |filepath|
          AssetHat.last_commit_id(filepath)
        end
      end
    end
  end

end