Add FragmentFilter (#177)

Co-authored-by: Will Cosgrove <[email protected]>

lib/phlex/rails.rb

@@ -17,6 +17,7 @@ module Rails
 		autoload :Layout, "phlex/rails/layout"
 		autoload :SGML, "phlex/rails/sgml"
 		autoload :UnbufferedOverrides, "phlex/rails/unbuffered_overrides"
+		autoload :FragmentFinder, "phlex/rails/fragment_finder"
 	end
 
 	CSV.prepend Phlex::Rails::CSV::Overrides

lib/phlex/rails/fragment_finder.rb

@@ -0,0 +1,28 @@
+# frozen_string_literal: true
+
+module Phlex::Rails::FragmentFinder
+	extend self
+
+	Parser = if defined?(Nokolexbor)
+		Nokolexbor
+	else
+		require "nokogiri"
+		Nokogiri::HTML
+	end
+
+	def extract(html, ids)
+		parsed = Parser.parse(html)
+		selector = ids.map { |id| "##{id}" }.join(", ")
+
+		result = +""
+
+		ids.count.times do
+			if (fragment = parsed.at_css(selector))
+				result << fragment.to_s
+				fragment.remove
+			end
+		end
+
+		result
+	end
+end

spec/fragment_filter_spec.rb

@@ -0,0 +1,37 @@
+# frozen_string_literal: true
+
+describe Phlex::Rails::FragmentFinder do
+	include	Phlex::Rails::FragmentFinder
+	it "find one" do
+		expect(
+			extract(<<~HTML, ["b"])
+				<div id="a">A</div>
+				<div id="b">B</div>
+				<div id="c">c</div>
+			HTML
+		).to be == %(<div id="b">B</div>)
+	end
+
+	it "find two" do
+		expect(
+			extract(<<~HTML, ["b", "c"])
+				<div id="a">A</div>
+				<div id="b">B</div>
+				<div id="c">C</div>
+				<div id="d">D</div>
+			HTML
+		).to be == %(<div id="b">B</div><div id="c">C</div>)
+	end
+
+	it "doesn't duplicate" do
+		expect(
+			extract(<<~HTML, ["b", "c"])
+				<div id="a">A</div>
+				<div id="b">B
+					<div id="c">C</div>
+				</div>
+				<div id="d">D</div>
+			HTML
+		).to be == %(<div id="b">B\n\t<div id="c">C</div>\n</div>)
+	end
+end