scan variables and fallback values from a string template

spec/lib/template_parser_spec.rb

@@ -5,15 +5,15 @@
 describe TemplateParser do
   context 'parse simple variables' do
     it 'returns a list with found variable' do
-      expect(TemplateParser.new("{{ variable }}").variables).to eq(['variable'])
+      expect(TemplateParser.new("{{ variable }}").variables).to eq([['variable', nil]])
     end
 
     it 'returns a list with all found variables' do
-      expect(TemplateParser.new("{{ variable }} abc xyz {{ another_variable }}").variables).to eq(['another_variable', 'variable'])
+      expect(TemplateParser.new("{{ variable }} abc xyz {{ another_variable }}").variables).to eq([['variable', nil], ['another_variable', nil]])
     end
 
     it 'returns a list with variables and fallback values' do
-      expect(TemplateParser.new("{{ variable }} abc xyz {{ another_variable | fallback: 'xpto' }}").variables).to eq([['another_variable', 'xpto'], ['variable']])
+      expect(TemplateParser.new("{{ variable }} abc xyz {{ another_variable | fallback: 'xpto' }}").variables).to eq([['variable', nil], ['another_variable', 'xpto']])
     end
   end
 end

src/lib/template_parser.rb

@@ -1,6 +1,6 @@
 class TemplateParser
   VARIABLES = /{{\s?([\w]*)\s?(\|\s?fallback:\s?'[\w ]*'\s?)?}}/
-  COMPONENTS = /{{\s[a-zA-Z0-9_ ]\s|\sfallback:\s'.?'\s*}}/
+  FALLBACK = /\|\s?fallback:\s?'([a-z0-9_]+)'\s?/
 
   attr_accessor :variables
 
@@ -12,7 +12,14 @@ def initialize(template)
   private
 
   def parse_variables
-    @variables ||= @template.scan(VARIABLES).map { |var, _| var.strip }.sort
+    @variables ||= @template.scan(VARIABLES).map do |variable, fallback|
+      if fallback.nil?
+        [variable, nil]
+      else
+        fallback_value = fallback.match(FALLBACK).captures.first
+        [variable, fallback_value]
+      end
+    end
   end
 
 end