Add handling of type filters and handling of ETags

Add API documentation and test cases around ETags for the API.

app/controllers/repp/v1/retained_domains_controller.rb

@@ -2,10 +2,14 @@ module Repp
   module V1
     class RetainedDomainsController < ActionController::API
       def index
-        domains = RetainedDomains.new
+        domains = RetainedDomains.new(query_params)
 
         render json: { count: domains.count, domains: domains.to_jsonable }
       end
+
+      def query_params
+        params.permit(:type)
+      end
     end
   end
 end

app/models/retained_domains.rb

@@ -4,26 +4,55 @@ class RetainedDomains
   RESERVED = 'reserved'.freeze
   BLOCKED = 'blocked'.freeze
 
-  attr_reader :domains
+  attr_reader :domains,
+              :type
 
-  def initialize
+  def initialize(params)
+    @type = establish_type(params)
     @domains = gather_domains
   end
 
-  def gather_domains
-    blocked_domains = BlockedDomain.order(name: :desc).all
-    reserved_domains = ReservedDomain.order(name: :desc).all
+  delegate :count, to: :domains
 
+  def to_jsonable
+    domains.map { |el| domain_to_jsonable(el) }
+  end
+
+  private
+
+  def establish_type(params)
+    type = params[:type]
+
+    case type
+    when 'reserved' then :reserved
+    when 'blocked' then :blocked
+    else :all
+    end
+  end
+
+  def gather_domains
     domains = blocked_domains.to_a.union(reserved_domains.to_a)
 
     domains.sort_by(&:name)
   end
 
-  def to_jsonable
-    domains.map { |el| domain_to_json(el) }
+  def blocked_domains
+    if %i[all blocked].include?(type)
+      BlockedDomain.order(name: :desc).all
+    else
+      []
+    end
   end
 
-  def domain_to_json(domain)
+  def reserved_domains
+    if %i[all reserved].include?(type)
+      ReservedDomain.order(name: :desc).all
+    else
+      []
+    end
+  end
+
+  def domain_to_jsonable(domain)
     status = case domain
              when ReservedDomain then RESERVED
              when BlockedDomain then BLOCKED
@@ -37,6 +66,4 @@ class RetainedDomains
       punycode_name: punycode,
     }
   end
-
-  delegate :count, to: :domains
 end