Adds a new mechanism to load providers from any gem or file path. (#263)

* Adds ability to load only providers used in config file

lib/vmpooler/providers.rb

@@ -1,7 +1,119 @@
-%w[base dummy vsphere].each do |lib|
-  begin
-    require "vmpooler/providers/#{lib}"
-  rescue LoadError
-    require File.expand_path(File.join(File.dirname(__FILE__), 'providers', lib))
+require 'pathname'
+
+module Vmpooler
+  class Providers
+
+    # @param names [Array] - an array of names or string name of a provider
+    # @return [Array] - list of provider files loaded
+    # ie. ["lib/vmpooler/providers/base.rb", "lib/vmpooler/providers/dummy.rb", "lib/vmpooler/providers/vsphere.rb"]
+    def self.load_by_name(names)
+      names = Array(names)
+      instance = self.new
+      names.map {|name| instance.load_from_gems(name)}.flatten
+    end
+
+    # @return [Array] - array of provider files
+    # ie. ["lib/vmpooler/providers/base.rb", "lib/vmpooler/providers/dummy.rb", "lib/vmpooler/providers/vsphere.rb"]
+    # although these files can come from any gem
+    def self.load_all_providers
+      self.new.load_from_gems
+    end
+
+    # @return [Array] - returns an array of gem names that contain a provider
+    def self.installed_providers
+      self.new.vmpooler_provider_gem_list.map(&:name)
+    end
+
+    # @return [Array] returns a list of vmpooler providers gem plugin specs
+    def vmpooler_provider_gem_list
+      gemspecs.find_all { |spec| File.directory?(File.join(spec.full_gem_path, provider_path)) } + included_lib_dirs
+    end
+
+    # Internal: Find any gems containing vmpooler provider plugins and load the main file in them.
+    #
+    # @return [Array[String]] - a array of provider files
+    # @param name [String] - the name of the provider to load
+    def load_from_gems(name = nil)
+      paths = gem_directories.map do |gem_path|
+        # we don't exactly know if the provider name matches the main file name that should be loaded
+        # so we use globs to get everything like the name
+        # this could mean that vsphere5 and vsphere6 are loaded when only vsphere5 is used
+        Dir.glob(File.join(gem_path, "*#{name}*.rb")).each do |file|
+          require file
+        end
+      end
+      paths.flatten
+    end
+
+    private
+
+    # @return [String] - the relative path to the vmpooler provider dir
+    # this is used when searching gems for this path
+    def provider_path
+      File.join('lib','vmpooler','providers')
+    end
+
+    # Add constants to array to skip over classes, ie. Vmpooler::PoolManager::Provider::Dummy
+    def excluded_classes
+      []
+    end
+
+    # paths to include in the search path
+    def included_lib_dirs
+      []
+    end
+
+    # returns an array of plugin classes by looking in the object space for all loaded classes
+    # that start with Vmpooler::PoolManager::Provider
+    def plugin_classes
+      unless @plugin_classes
+        load_plugins
+        # weed out any subclasses in the formatter
+        klasses = ObjectSpace.each_object(Class).find_all do |c|
+          c.name && c.name.split('::').count == 3 && c.name =~ /Vmpooler::PoolManager::Provider/
+        end
+        @plugin_classes = klasses - excluded_classes || []
+      end
+      @plugin_classes
+    end
+
+    def plugin_map
+      @plugin_map ||= Hash[plugin_classes.map { |gem| [gem.send(:name), gem] }]
+    end
+
+
+
+    # Internal: Retrieve a list of available gem paths from RubyGems.
+    #
+    # Returns an Array of Pathname objects.
+    def gem_directories
+      dirs = []
+      if has_rubygems?
+        dirs = gemspecs.map do |spec|
+          lib_path = File.expand_path(File.join(spec.full_gem_path,provider_path))
+          lib_path if File.exists? lib_path
+        end + included_lib_dirs
+      end
+      dirs.reject { |dir| dir.nil? }.uniq
+    end
+
+    # Internal: Check if RubyGems is loaded and available.
+    #
+    # Returns true if RubyGems is available, false if not.
+    def has_rubygems?
+      defined? ::Gem
+    end
+
+    # Internal: Retrieve a list of available gemspecs.
+    #
+    # Returns an Array of Gem::Specification objects.
+    def gemspecs
+      @gemspecs ||= if Gem::Specification.respond_to?(:latest_specs)
+                      Gem::Specification.latest_specs
+                    else
+                      Gem.searcher.init_gemspecs
+                    end
+    end
+
   end
 end