Adding a Qa::Authorities::Loc.type_for

Prior to this commit, we always assumed that each "find" would request
from `https://id.loc.gov/authorities`.

With this commit, we use the "subauthority" to inform what the base URL
is for the `https://id.loc.gov/` host.  In some cases this is
`authorities` and in others it's as the code indicates.

lib/qa/authorities/loc.rb

@@ -14,5 +14,17 @@ def self.subauthority_for(subauthority)
     def self.subauthorities
       authorities + vocabularies + datatypes + preservation
     end
+
+    # @note The returned value is the root directory of the URL.  The graphicMaterials sub-authority
+    #       has a "type" of vocabulary.  https://id.loc.gov/vocabulary/graphicMaterials/tgm008083.html
+    #       In some cases, this is plural and in others this is singular.
+    # @return [String]
+    def self.type_for(subauthority:)
+      validate_subauthority!(subauthority)
+      return "authorities" if authorities.include?(subauthority)
+      return "vocabulary" if vocabularies.include?(subauthority)
+      return "datatype" if datatypes.include?(subauthority)
+      return "preservation" if preservation.include?(subauthority)
+    end
   end
 end

lib/qa/authorities/loc/generic_authority.rb

@@ -4,6 +4,7 @@ class Loc::GenericAuthority < Base
     def initialize(subauthority)
       super()
       @subauthority = subauthority
+      @subauthority_type = Loc.type_for(subauthority: subauthority)
     end
 
     include WebServiceBase
@@ -35,7 +36,7 @@ def find(id)
     end
 
     def find_url(id)
-      "https://id.loc.gov/authorities/#{@subauthority}/#{id}.json"
+      "https://id.loc.gov/#{@subauthority_type}/#{@subauthority}/#{id}.json"
     end
 
     private

lib/qa/authorities/loc_subauthority.rb

@@ -1,4 +1,5 @@
 module Qa::Authorities::LocSubauthority
+  # @todo Rename to reflect that this is a URI encoded url fragement used only for searching.
   def get_url_for_authority(authority)
     if authorities.include?(authority) then authority_base_url
     elsif vocabularies.include?(authority) then vocab_base_url

spec/lib/authorities/loc_spec.rb

@@ -42,6 +42,18 @@
     end
   end
 
+  describe ".type_for" do
+    it "raises an error for an invalid subauthority" do
+      expect do
+        described_class.type_for(subauthority: "no-one-would-ever-have-this-one")
+      end.to raise_error Qa::InvalidSubAuthority
+    end
+
+    it "returns the corresponding type for the given subauthority" do
+      expect(described_class.type_for(subauthority: "graphicMaterials")).to eq("vocabulary")
+    end
+  end
+
   describe "#response" do
     subject { authority.response(url) }
     let :authority do