module MCollective
  # A simple plugin manager, it stores one plugin each of a specific type
  # the idea is that we can only have one security provider, one connector etc.
  module PluginManager
    @plugins = {}

    # Adds a plugin to the list of plugins, we expect a hash like:
    #
    #    {:type => "base",
    #     :class => foo.new}
    #
    # or like:
    #    {:type => "base",
    #     :class => "Foo::Bar"}
    #
    # In the event that we already have a class with the given type
    # an exception will be raised.
    #
    # If the :class passed is a String then we will delay instantiation
    # till the first time someone asks for the plugin, this is because most likely
    # the registration gets done by inherited() hooks, at which point the plugin class is not final.
    #
    # If we were to do a .new here the Class initialize method would get called and not
    # the plugins, we there for only initialize the classes when they get requested via []
    #
    # By default all plugin instances are cached and returned later so there's
    # always a single instance.  You can pass :single_instance => false when
    # calling this to instruct it to always return a new instance when a copy
    # is requested.  This only works with sending a String for :class.
    def self.<<(plugin)
      plugin[:single_instance] = true unless plugin.include?(:single_instance)

      type = plugin[:type]
      klass = plugin[:class]
      single = plugin[:single_instance]

      raise("Plugin #{type} already loaded") if @plugins.include?(type)


      # If we get a string then store 'nil' as the instance, signalling that we'll
      # create the class later on demand.
      if klass.is_a?(String)
        @plugins[type] = {:loadtime => Time.now, :class => klass, :instance => nil, :single => single}
        Log.debug("Registering plugin #{type} with class #{klass} single_instance: #{single}")
      else
        @plugins[type] = {:loadtime => Time.now, :class => klass.class, :instance => klass, :single => true}
        Log.debug("Registering plugin #{type} with class #{klass.class} single_instance: true")
      end
    end

    # Removes a plugim the list
    def self.delete(plugin)
      @plugins.delete(plugin) if @plugins.include?(plugin)
    end

    # Finds out if we have a plugin with the given name
    def self.include?(plugin)
      @plugins.include?(plugin)
    end

    # Provides a list of plugins we know about
    def self.pluginlist
      @plugins.keys.sort
    end

    # deletes all registered plugins
    def self.clear
      @plugins.clear
    end

    # Gets a plugin by type
    def self.[](plugin)
      raise("No plugin #{plugin} defined") unless @plugins.include?(plugin)

      klass = @plugins[plugin][:class]

      if @plugins[plugin][:single]
        # Create an instance of the class if one hasn't been done before
        if @plugins[plugin][:instance] == nil
          Log.debug("Returning new plugin #{plugin} with class #{klass}")
          @plugins[plugin][:instance] = create_instance(klass)
        else
          Log.debug("Returning cached plugin #{plugin} with class #{klass}")
        end

        @plugins[plugin][:instance]
      else
        Log.debug("Returning new plugin #{plugin} with class #{klass}")
        create_instance(klass)
      end
    end

    # use eval to create an instance of a class
    def self.create_instance(klass)
      begin
        eval("#{klass}.new")
      rescue Exception => e
        raise("Could not create instance of plugin #{klass}: #{e}")
      end
    end

    # Finds plugins in all configured libdirs
    #
    #   find("agent")
    #
    # will return an array of just agent names, for example:
    #
    #   ["puppetd", "package"]
    #
    # Can also be used to find files of other extensions:
    #
    #   find("agent", "ddl")
    #
    # Will return the same list but only of files with extension .ddl
    # in the agent subdirectory
    def self.find(type, extension="rb")
      extension = ".#{extension}" unless extension.match(/^\./)

      plugins = []

      Config.instance.libdir.each do |libdir|
        plugdir = File.join([libdir, "mcollective", type.to_s])
        next unless File.directory?(plugdir)

        Dir.new(plugdir).grep(/#{extension}$/).map do |plugin|
          plugins << File.basename(plugin, extension)
        end
      end

      plugins.sort.uniq
    end

    # Finds and loads from disk all plugins from all libdirs that match
    # certain criteria.
    #
    #    find_and_load("pluginpackager")
    #
    # Will find all .rb files in the libdir/mcollective/pluginpackager/
    # directory in all libdirs and load them from disk.
    #
    # You can influence what plugins get loaded using a block notation:
    #
    #    find_and_load("pluginpackager") do |plugin|
    #       plugin.match(/puppet/)
    #    end
    #
    # This will load only plugins matching /puppet/
    def self.find_and_load(type, extension="rb")
      extension = ".#{extension}" unless extension.match(/^\./)

      klasses = find(type, extension).map do |plugin|
        if block_given?
          next unless yield(plugin)
        end

        "%s::%s::%s" % [ "MCollective", type.capitalize, plugin.capitalize ]
      end.compact

      klasses.sort.uniq.each {|klass| loadclass(klass, true)}
    end

    # Loads a class from file by doing some simple search/replace
    # on class names and then doing a require.
    def self.loadclass(klass, squash_failures=false)
      fname = klass.gsub("::", "/").downcase + ".rb"

      Log.debug("Loading #{klass} from #{fname}")

      load fname
    rescue Exception => e
      Log.error("Failed to load #{klass}: #{e}")
      raise unless squash_failures
    end

    # Grep's over the plugin list and returns the list found
    def self.grep(regex)
      @plugins.keys.grep(regex)
    end
  end
end