🐛 Work through fallback of rodeo URLs

This commit replaces raising exceptions when we can't derive the URL.
Instead it opts to return nil and let the caller determine what to do.

The primary result is that it's easier to have a rodeo configuration
"miss" finding files in the pre-process location due to configuration
issues.

But alas, that's the nature of a rodeo.

Related to:

- #294

app/services/iiif_print/derivative_rodeo_service.rb

@@ -82,7 +82,8 @@ def named_derivatives_and_generators
     # @param adapter_name [String] Added as a parameter to make testing just a bit easier.  See
     #        {.preprocessed_location_adapter_name}
     #
-    # @return [String]
+    # @return [String] when we have a possible candidate.
+    # @return [NilClass] when we could not derive a candidate.
     # rubocop:disable Metrics/MethodLength
     def self.derivative_rodeo_uri(file_set:, filename: nil, extension: nil, adapter_name: preprocessed_location_adapter_name)
       # TODO: This is a hack that knows about the inner workings of Hydra::Works, but for
@@ -91,6 +92,7 @@ def self.derivative_rodeo_uri(file_set:, filename: nil, extension: nil, adapter_
       filename ||= Hydra::Works::DetermineOriginalName.call(file_set.original_file)
 
       dirname = derivative_rodeo_preprocessed_directory_for(file_set: file_set, filename: filename)
+      return nil unless dirname
 
       # The aforementioned filename and the following basename and extension are here to allow for
       # us to take an original file and see if we've pre-processed the derivative file.  In the
@@ -141,6 +143,7 @@ def self.get_ancestor(filename: nil, file_set:)
     # @param file_set [FileSet]
     # @param filename [String]
     # @return [String] the dirname (without any "/" we hope)
+    # @return [NilClass] when we cannot infer a URI from the object.
     def self.derivative_rodeo_preprocessed_directory_for(file_set:, filename:)
       ancestor, ancestor_type = get_ancestor(filename: filename, file_set: file_set)
 
@@ -152,16 +155,19 @@ def self.derivative_rodeo_preprocessed_directory_for(file_set:, filename:)
         message = "#{self.class}.#{__method__} #{file_set.class} ID=#{file_set.id} and filename: #{filename.inspect}" \
                   "has #{ancestor_type} of #{ancestor.class} ID=#{ancestor.id}"
         Rails.logger.info(message)
-        ancestor.public_send(parent_work_identifier_property_name) ||
-          raise("Expected #{ancestor.class} ID=#{ancestor.id} (#{ancestor_type} of #{file_set.class} ID=#{file_set.id}) " \
-                "to have a present #{parent_work_identifier_property_name.inspect}")
+        parent_work_identifier = ancestor.public_send(parent_work_identifier_property_name)
+        return parent_work_identifier if parent_work_identifier.present?
+        Rails.logger.warn("Expected #{ancestor.class} ID=#{ancestor.id} (#{ancestor_type} of #{file_set.class} ID=#{file_set.id}) " \
+                          "to have a present #{parent_work_identifier_property_name.inspect}")
+        nil
       else
         # HACK: This makes critical assumptions about how we're creating the title for the file_set;
         # but we don't have much to fall-back on.  Consider making this a configurable function.  Or
         # perhaps this entire method should be more configurable.
         # TODO: Revisit this implementation.
-        file_set.title.first.split(".").first ||
-          raise("#{file_set.class} ID=#{file_set.id} has title #{file_set.title.first} from which we cannot infer information.")
+        candidate = file_set.title.first.split(".").first
+        return candidate if candidate.present?
+        nil
       end
       # rubocop:enable Style/GuardClause
     end

lib/iiif_print/split_pdfs/derivative_rodeo_splitter.rb

@@ -84,7 +84,13 @@ def preprocessed_location_template
         derivative_rodeo_candidate = IiifPrint::DerivativeRodeoService.derivative_rodeo_uri(file_set: file_set, filename: filename)
 
         @preprocessed_location_template =
-          if rodeo_conformant_uri_exists?(derivative_rodeo_candidate)
+          if derivative_rodeo_candidate.blank?
+            message = "#{self.class}##{__method__} could not establish derivative_rodeo_candidate for " \
+                      "#{file_set.class} ID=#{file_set&.id} #to_param=#{file_set&.to_param} with filename #{filename.inspect}.  " \
+                      "Move along little buddy."
+            Rails.logger.debug(message)
+            nil
+          elsif rodeo_conformant_uri_exists?(derivative_rodeo_candidate)
             Rails.logger.debug("#{self.class}##{__method__} found existing file at location #{derivative_rodeo_candidate}.  High five partner!")
             derivative_rodeo_candidate
           elsif file_set.import_url
@@ -94,7 +100,8 @@ def preprocessed_location_template
             handle_original_file_not_in_derivative_rodeo
           else
             message = "#{self.class}##{__method__} could not find an existing file at #{derivative_rodeo_candidate} " \
-                      "nor a remote_url for #{file_set.class} ID=#{file_set.id}.  Returning `nil' as we have no possible preprocess.  " \
+                      "nor a remote_url for #{file_set.class} ID=#{file_set.id} #to_param=#{file_set&.to_param}.  " \
+                      "Returning `nil' as we have no possible preprocess.  " \
                       "Maybe the input_uri #{input_uri.inspect} will be adequate."
             Rails.logger.warn(message)
             nil
@@ -146,7 +153,7 @@ def split_files
       rescue => e
         message = "#{self.class}##{__method__} encountered `#{e.class}' “#{e}” for " \
                   "input_uri: #{input_uri.inspect}, " \
-                  "output_location_template: #{output_location_template.inspect}, and" \
+                  "output_location_template: #{output_location_template.inspect}, and " \
                   "preprocessed_location_template: #{preprocessed_location_template.inspect}."
         exception = RuntimeError.new(message)
         exception.set_backtrace(e.backtrace)