Add FilterArray class to Banzai

lib/banzai/filter_array.rb

+module Banzai
+  class FilterArray < Array
+    # Insert a value immediately after another value
+    #
+    # If the preceding value does not exist, the new value is added to the end
+    # of the Array.
+    def insert_after(after_value, value)
+      i = index(after_value) || length - 1
+
+      insert(i + 1, value)
+    end
+
+    # Insert a value immediately before another value
+    #
+    # If the succeeding value does not exist, the new value is added to the
+    # beginning of the Array.
+    def insert_before(before_value, value)
+      i = index(before_value) || -1
+
+      if i < 0
+        unshift(value)
+      else
+        insert(i, value)
+      end
+    end
+  end
+end

lib/banzai/pipeline/base_pipeline.rb

@@ -4,7 +4,7 @@ module Banzai
   module Pipeline
     class BasePipeline
       def self.filters
-        []
+        FilterArray[]
       end
 
       def self.transform_context(context)

lib/banzai/pipeline/broadcast_message_pipeline.rb

@@ -2,7 +2,7 @@ module Banzai
   module Pipeline
     class BroadcastMessagePipeline < DescriptionPipeline
       def self.filters
-        @filters ||= [
+        @filters ||= FilterArray[
           Filter::MarkdownFilter,
           Filter::SanitizationFilter,
 

lib/banzai/pipeline/combined_pipeline.rb

@@ -10,7 +10,7 @@ module Banzai
           end
 
           def self.filters
-            pipelines.flat_map(&:filters)
+            FilterArray.new(pipelines.flat_map(&:filters))
           end
 
           def self.transform_context(context)

lib/banzai/pipeline/gfm_pipeline.rb

@@ -2,7 +2,7 @@ module Banzai
   module Pipeline
     class GfmPipeline < BasePipeline
       def self.filters
-        @filters ||= [
+        @filters ||= FilterArray[
           Filter::SyntaxHighlightFilter,
           Filter::SanitizationFilter,
 

lib/banzai/pipeline/plain_markdown_pipeline.rb

@@ -2,7 +2,7 @@ module Banzai
   module Pipeline
     class PlainMarkdownPipeline < BasePipeline
       def self.filters
-        [
+        FilterArray[
           Filter::MarkdownFilter
         ]
       end

lib/banzai/pipeline/post_process_pipeline.rb

@@ -2,7 +2,7 @@ module Banzai
   module Pipeline
     class PostProcessPipeline < BasePipeline
       def self.filters
-        [
+        FilterArray[
           Filter::RelativeLinkFilter,
           Filter::RedactorFilter
         ]

lib/banzai/pipeline/reference_extraction_pipeline.rb

@@ -2,7 +2,7 @@ module Banzai
   module Pipeline
     class ReferenceExtractionPipeline < BasePipeline
       def self.filters
-        [
+        FilterArray[
           Filter::ReferenceGathererFilter
         ]
       end

lib/banzai/pipeline/single_line_pipeline.rb

@@ -2,7 +2,7 @@ module Banzai
   module Pipeline
     class SingleLinePipeline < GfmPipeline
       def self.filters
-        @filters ||= [
+        @filters ||= FilterArray[
           Filter::SanitizationFilter,
 
           Filter::EmojiFilter,

lib/banzai/pipeline/wiki_pipeline.rb

@@ -4,11 +4,8 @@ module Banzai
   module Pipeline
     class WikiPipeline < FullPipeline
       def self.filters
-        @filters ||= begin
-                       filters = super
-                       toc = filters.index(Filter::TableOfContentsFilter)
-                       filters.insert(toc + 1, Filter::GollumTagsFilter)
-                     end
+        @filters ||= super.insert_after(Filter::TableOfContentsFilter,
+                                        Filter::GollumTagsFilter)
       end
     end
   end

spec/lib/banzai/filter_array_spec.rb

+require 'spec_helper'
+
+describe Banzai::FilterArray do
+  describe '#insert_after' do
+    it 'inserts an element after a provided element' do
+      filters = described_class.new(%w(a b c))
+
+      filters.insert_after('b', '1')
+
+      expect(filters).to eq %w(a b 1 c)
+    end
+
+    it 'inserts an element at the end when the provided element does not exist' do
+      filters = described_class.new(%w(a b c))
+
+      filters.insert_after('d', '1')
+
+      expect(filters).to eq %w(a b c 1)
+    end
+  end
+
+  describe '#insert_before' do
+    it 'inserts an element before a provided element' do
+      filters = described_class.new(%w(a b c))
+
+      filters.insert_before('b', '1')
+
+      expect(filters).to eq %w(a 1 b c)
+    end
+
+    it 'inserts an element at the beginning when the provided element does not exist' do
+      filters = described_class.new(%w(a b c))
+
+      filters.insert_before('d', '1')
+
+      expect(filters).to eq %w(1 a b c)
+    end
+  end
+end