Add option to only generate hashtags if a specific condition is met

README.md

@@ -68,6 +68,30 @@ class Picture < ActiveRecord::Base
 end
 ```
 
+If you only want hashtags created based on conditions,
+you can create a guard with `hashtag_if`:
+
+```ruby
+class Post < ActiveRecord::Base
+  include SimpleHashtag::Hashtaggable
+
+  hashtag_if ->(post) { post.body =~ /ruby/ }
+end
+
+# or...
+
+class Post < ActiveRecord::Base
+  include SimpleHashtag::Hashtaggable
+
+  hashtag_if :about_ruby?
+
+  def about_ruby?
+    body =~ /ruby/
+  end
+end
+```
+
+
 From here on, if your text contains a hashtag, say _#RubyRocks_,
 _Simple Hasthag_ will find it, store it in a table and retreive it and its associated object if asked.
 Helpers are also available to create a link when displaying the text.

lib/simple_hashtag/hashtaggable.rb

@@ -2,6 +2,8 @@ module SimpleHashtag
   module Hashtaggable
     extend ActiveSupport::Concern
 
+    class InvalidHashtagGuard < ArgumentError; end
+
     included do
       has_many :hashtaggings, as: :hashtaggable,  class_name: "SimpleHashtag::Hashtagging", dependent: :destroy
       has_many :hashtags, through: :hashtaggings, class_name: "SimpleHashtag::Hashtag"
@@ -15,9 +17,23 @@ def hashtaggable_content
       end
 
       def update_hashtags
+        if hashtag_guard.present?
+          if hashtag_guard.respond_to?(:call)
+            return unless hashtag_guard.call self
+          elsif self.respond_to? hashtag_guard
+            return unless self.send hashtag_guard
+          else
+            raise InvalidHashtagGuard
+          end
+        end
+
         self.hashtags = parsed_hashtags
       end
 
+      def hashtag_guard
+        self.class.hashtag_guard
+      end
+
       def parsed_hashtags
         parsed_hashtags = []
         array_of_hashtags_as_string = scan_for_hashtags(hashtaggable_content)
@@ -36,10 +52,15 @@ def scan_for_hashtags(content)
 
     module ClassMethods
       attr_accessor :hashtaggable_attribute_name
+      attr_accessor :hashtag_guard
 
       def hashtaggable_attribute(name=nil)
         self.hashtaggable_attribute_name ||= name || :body
       end
+
+      def hashtag_if(guard)
+        self.hashtag_guard = guard
+      end
     end
   end
 end

spec/simple_hashtag_spec.rb

@@ -134,5 +134,54 @@
       h.name.should eq "chance"
       h.hashtaggables.count.should eq 2
      end
+
+    context "with a lamdba guard" do
+      class GuardedPost < Post
+        hashtag_if lambda { |post| post.body =~ /Community/ }
+      end
+
+      it "creates hashtags if the guard is fulfilled" do
+        GuardedPost.create(body: 'Community saved! #sixseasonsandamovie')
+        p = Post.last
+        p.hashtags.first.name.should eq 'sixseasonsandamovie'
+      end
+
+      it "does not create hashtags if the guard is notfulfilled" do
+        GuardedPost.create(body: 'To boldly go... #startrek')
+        p = Post.last
+        p.hashtags.should == []
+      end
+    end
+
+    context "with a method guard" do
+      class MethodGuardedPost < Post
+        hashtag_if :is_community?
+
+        def is_community?
+          body =~ /Community/
+        end
+      end
+
+      it "creates hashtags if the guard is fulfilled" do
+        MethodGuardedPost.create(body: 'Community saved! #sixseasonsandamovie')
+        Post.last.hashtags.first.name.should eq 'sixseasonsandamovie'
+      end
+
+      it "does not create hashtags if the guard is notfulfilled" do
+        MethodGuardedPost.create(body: 'To boldly go... #startrek')
+        Post.last.hashtags.should == []
+      end
+    end
+
+    context "with an invalid guard" do
+      class PoorlyGuardedPost < Post
+        hashtag_if :this_isnt_even_real
+      end
+    end
+
+    it "raises an error" do
+      p = PoorlyGuardedPost.new(body: '#doesntmatter #thisisgoingtofail')
+      expect{ p.save! }.to raise_error SimpleHashtag::Hashtaggable::InvalidHashtagGuard
+    end
   end
 end