module Indexer

  module Loadable

    #
    # Open metadata file and ensure strict validation to canonical format.
    #
    # @param [String] file or directory
    #   The file name from which to read the YAML metadata,
    #   or a directory from which to lookup the file.
    #
    def open(file=Dir.pwd)
      file = find(file) if File.directory?(file)
      valid(YAML.load_file(file))
    end

    #
    # Like #open, but do not ensure strict validation to canonical format.
    #
    # @param [String] file or directory
    #   The file name from which to read the YAML metadata,
    #   or a directory from which to lookup the file.
    #
    def read(file=Dir.pwd)
      file = find(file) if File.directory?(file)
      new(YAML.load_file(file))  
    end

    #
    # Create new Metadata instance from atypical sources.
    #
    # TODO: Use Importer to construct Metadata instance.
    #
    def import(*sources)
    end

    #
    # Load from YAML string or IO.
    #
    # @param [String,#read] String or IO object
    #   The file name from which to read the YAML metadata.
    #
    def load(io)
      new(YAML.load(io))
    end

    #
    # Load from YAML file.
    #
    # @param [String] file
    #   The file name from which to read the YAML metadata.
    #
    def load_file(file)
      new(YAML.load_file(file))
    end

    #
    # Find project root and read the index file.
    #
    # @param [String] from
    #   The directory from which to start the upward search.
    #
    def find(from=Dir.pwd)
      File.join(root(from), LOCK_FILE)
    end

    #
    # Find project root by looking upward for a locked metadata file.
    #
    # @param [String] from
    #   The directory from which to start the upward search.
    #
    # @return [String]
    #   The path to the locked metadata file.
    #
    # @raise [Errno::ENOENT]
    #   The locked metadata file could not be located.
    #
    def root(from=Dir.pwd)
      if not path = exists?(from)
        lock_file_missing(from)
      end
      path
    end

    #
    # Does a locked metadata file exist?
    #
    # @return [true,false] Whether locked metadata file exists.
    #
    def exists?(from=Dir.pwd)
      home = File.expand_path('~')
      path = File.expand_path(from)
      while path != '/' and path != home
        if File.file?(File.join(path,LOCK_FILE))
          return path
        else
          path = File.dirname(path)
        end
        false #lock_file_missing(from)
      end
      false #lock_file_missing(from)
    end

    #
    # Raise lock file missing error.
    #
    def lock_file_missing(from=nil)
      raise Error.exception("could not locate .index file", Errno::ENOENT)
    end

    #
    # Alias for exists?
    #
    def exist?(from=Dir.pwd)
      exists?(from)
    end

    #
    # Lockdown the metadata (via Importer) and return updated metadata.
    #
    # Options :force
    #
    def lock(*sources)
      opts = (Hash === sources.last ? sources.pop : {})

      file    = nil
      needed  = true
      sources = sources.flatten

      if sources.empty?
        if file = exists?
          metadata = Metadata.open
          sources = metadata.sources
        else
          sources = Dir.glob(USER_FILES, File::FNM_CASEFOLD)
          raise Error.exception("could not find default sources") if sources.empty?
        end
      end

      if file && !opts[:force]
        date = sources.map{ |s| File.mtime(s) }.max
        needed = false if File.mtime(file) > date
      end

      Importer.import(*sources) if needed
    end

    #
    # Lockdown the metadata (via Importer) and save.
    #
    def lock!(*sources)
      metadata = lock(*sources)
      metadata.save! if metadata
    end

  end

end