Extend stacks identifiers to smuggle additional attributes

app/controllers/iiif_controller.rb

@@ -146,7 +146,7 @@ def transformation
   end
 
   def stacks_identifier
-    @stacks_identifier ||= StacksIdentifier.new(escaped_identifier.sub(/^degraded_/, '') + '.jp2')
+    @stacks_identifier ||= StacksIdentifier.new(escaped_identifier.sub(/^degraded_/, ''), file_ext: 'jp2')
   end
 
   def canonical_params

app/models/stacks_identifier.rb

@@ -2,19 +2,26 @@
 
 # The identifier of a stacks resource
 class StacksIdentifier
-  def initialize(options = {})
-    if options.is_a? String
-      parse_identifer(options)
-    elsif options[:id]
-      parse_identifer(options[:id])
-    elsif options[:druid] && options[:file_name]
-      self.druid = options[:druid]
-      @file_name = options[:file_name]
+  attr_reader :druid, :file_name, :options
+
+  OPTIONS_DELIMITER = '%2F!attr!%2F'
+  def initialize(identifier = nil, id: nil, druid: nil, file_name: nil, file_ext: nil, **options)
+    if identifier
+      parse_identifer(identifier, file_ext)
+    elsif id
+      parse_identifer(id, file_ext)
+    elsif druid && file_name
+      self.druid = druid
+      @file_name = [file_name, file_ext.presence].compact.join('.')
     end
+    @options = (@options || {}).merge(options)
   end
 
   def to_s
-    [@druid, @file_name].join('%2F')
+    identifier_part = [@druid, @file_name].join('%2F')
+    options_part = @options.map { |k, v| "#{k}=#{v}" }.join('%2F')
+
+    [identifier_part, options_part.presence].compact.join(OPTIONS_DELIMITER)
   end
 
   def ==(other)
@@ -37,8 +44,6 @@ def treeified_path
     File.join(druid_parts[1..4], file_name)
   end
 
-  attr_reader :druid, :file_name
-
   private
 
   attr_reader :druid_parts
@@ -49,8 +54,14 @@ def druid=(druid)
     @druid_parts = match
   end
 
-  def parse_identifer(id)
-    druid, @file_name = id.split('%2F', 2)
+  def parse_identifer(id, file_ext)
+    identifier_and_file_name, attrs = id.split(OPTIONS_DELIMITER, 2)
+    druid, file_name = identifier_and_file_name.split('%2F', 2)
     self.druid = druid
+    @file_name = [file_name, file_ext.presence].compact.join('.')
+
+    if attrs.present?
+      @options = attrs.split('%2F').map { |x| x.split('=', 2) }.to_h
+    end
   end
 end

spec/models/stacks_identifier_spec.rb

@@ -32,4 +32,19 @@
     subject { instance.treeified_path }
     it { is_expected.to eq 'nr/349/ct/7889/nr349ct7889_00_0001.jp2' }
   end
+
+  context 'with some optional attributes' do
+    let(:instance) { described_class.new identifier }
+    let(:identifier) { 'nr349ct7889%2Fnr349ct7889_00_0001%2F!attr!%2Fversion=2'}
+
+    it 'parses out the right data' do
+      expect(instance.druid).to eq 'nr349ct7889'
+      expect(instance.file_name_without_ext).to eq 'nr349ct7889_00_0001'
+      expect(instance.options['version']).to eq '2'
+    end
+
+    it 'reserializes to the original value' do
+      expect(instance.to_s).to eq identifier
+    end
+  end
 end