defining parser inheritance chain

lib/planet/blog.rb

@@ -16,10 +16,12 @@ def initialize(attributes = {})
       self.twitter = attributes[:twitter]
       self.posts = attributes.fetch(:posts, [])
       self.planet = attributes[:planet]
+
+      @parsers = Parsers.new
     end
 
     def fetch
-      parser = self.type ? Parsers.get_parser(self.type) : Parsers.get_parser_for(self.feed)
+      parser = self.type ? @parsers.get_parser(self.type) : @parsers.get_parser_for(self.feed)
 
       feed = parser.fetch_and_parse(self.feed)
 

lib/planet/parsers.rb

@@ -1,25 +1,52 @@
 require 'feedzirra'
+require 'set'
 
 class Planet
   class Parsers
-    @@parsers = []
+    @@parsers = Set.new
+
+    def self.add_parser(parser)
+      @@parsers << parser
+    end
+
+    def initialize
+      @types, @domains = {}, {}
 
-    def self.get_parser(type)
       @@parsers.each do |parser|
-        return parser if parser.type == type
+        new_type, new_domains = parser.type, parser.domains
+
+        fail("duplicate type") if new_type and @types.has_key? new_type
+        fail("overlapping domains") unless (@domains.keys & new_domains).empty?
+
+        @types[new_type] = parser if new_type
+        new_domains.each do |new_domain|
+          @domains[new_domain] = parser
+        end
       end
+    end
 
-      raise ArgumentError, "no parser for type '#{ type }'", caller
+    def get_parser(type)
+      begin
+        return @types.fetch(type)
+      rescue KeyError => e
+        raise(ArgumentError, "No parser for type '#{ type }'", caller)
+      end
     end
 
-    def self.get_parser_for(feed)
+    def get_parser_for(feed)
       feed_domain = URI(feed).host
 
-      @@parsers.each do |parser|
-        return parser if parser.domains.any? { |domain| feed_domain.end_with? domain }
+      @domains.each do |domain, parser|
+        return parser if feed_domain.end_with? domain
       end
 
-      return Feedzirra::Feed
+      return Feedzirra::Feed # default generic parser
     end
   end
 end
+
+# load parsers
+dirname = File.join([File.dirname(__FILE__), 'parsers'])
+Dir.open(dirname).each do |filename|
+  require "#{dirname}/#{filename}" if filename.end_with? '.rb'
+end

lib/planet/parsers/base_parser.rb

@@ -0,0 +1,21 @@
+class Planet
+  class Parsers
+    class BaseParser
+      def self.type
+        @type
+      end
+
+      def self.domains
+        @domains || []
+      end
+
+      def self.inherited(parser)
+        Parsers.add_parser parser
+      end
+
+      def self.fetch_and_parse(feed)
+        raise(Exception, "Not implemented", caller)
+      end
+    end
+  end
+end