Make use of generics instead of a method

Allows Crystal to more accurately know the return type of `ordered_elements`
Add example of `ordered_elements` usage

spec/negotiator_spec.cr

@@ -112,6 +112,8 @@ struct NegotiatorTest < NegotiatorTestCase
   def test_ordered_elements(header : String, expected : Indexable(String)) : Nil
     elements = @negotiator.ordered_elements header
 
+    elements.should be_a Array(ANG::Accept)
+
     expected.each_with_index do |element, idx|
       elements[idx].should be_a ANG::Accept
       element.should eq elements[idx].header

src/abstract_negotiator.cr

@@ -1,5 +1,5 @@
 # Base negotiator type.  Implements logic common to all negotiators.
-abstract class Athena::Negotiation::AbstractNegotiator
+abstract class Athena::Negotiation::AbstractNegotiator(HeaderType)
   private record OrderKey, quality : Float32, index : Int32, value : String do
     include Comparable(self)
 
@@ -9,24 +9,22 @@ abstract class Athena::Negotiation::AbstractNegotiator
     end
   end
 
-  private abstract def create_header(header : String) : ANG::BaseAccept
+  # Returns the best `HeaderType` type based on the provided *header* value and *priorities*.
-
-  # Returns the best `ANG::BaseAccept` type based on the provided *header* value and *priorities*.
   #
   # See `Athena::Negotiation` for examples.
-  def best(header : String, priorities : Indexable(String), strict : Bool = false) : ANG::BaseAccept?
+  def best(header : String, priorities : Indexable(String), strict : Bool = false) : HeaderType?
     raise ArgumentError.new "priorities should not be empty." if priorities.empty?
     raise ArgumentError.new "The header string should not be empty." if header.blank?
 
-    accepted_headers = Array(ANG::BaseAccept).new
+    accepted_headers = Array(HeaderType).new
 
     self.parse_header(header) do |h|
-      accepted_headers << self.create_header h
+      accepted_headers << HeaderType.new h
     rescue ex
       raise ex if strict
     end
 
-    accepted_priorties = priorities.map &->create_header(String)
+    accepted_priorties = priorities.map { |p| HeaderType.new p }
 
     matches = self.find_matches accepted_headers, accepted_priorties
 
@@ -41,18 +39,28 @@ abstract class Athena::Negotiation::AbstractNegotiator
     match.nil? ? nil : accepted_priorties[match.index]
   end
 
-  # Returns an array of `ANG::BaseAccept` types that the provided *header* allows, ordered so that the `#best` match is first.
+  # Returns an array of `HeaderType` types that the provided *header* allows, ordered so that the `#best` match is first.
   #
-  # See `Athena::Negotiation` for examples.
+  # ```
-  def ordered_elements(header : String) : Array(ANG::BaseAccept)
+  # header = "text/*;q=0.3, text/html;q=0.7, text/html;level=1, text/html;level=2;q=0.4, */*;q=0.5"
+  #
+  # ordered_elements = ANG.negotiator.ordered_elements header
+  #
+  # ordered_elements[0].media_range # => "text/html"
+  # ordered_elements[1].media_range # => "text/html"
+  # ordered_elements[2].media_range # => "*/*"
+  # ordered_elements[3].media_range # => "text/html"
+  # ordered_elements[4].media_range # => "text/*"
+  # ```
+  def ordered_elements(header : String) : Array(HeaderType)
     raise ArgumentError.new "The header string should not be empty." if header.blank?
 
-    elements = Array(ANG::BaseAccept).new
+    elements = Array(HeaderType).new
     order_keys = Array(OrderKey).new
 
     idx = 0
     self.parse_header(header) do |h|
-      element = self.create_header h
+      element = HeaderType.new h
       elements << element
       order_keys << OrderKey.new element.quality, idx, element.header
     rescue ex
@@ -85,7 +93,7 @@ abstract class Athena::Negotiation::AbstractNegotiator
     end
   end
 
-  private def find_matches(headers : Array(ANG::BaseAccept), priorities : Indexable(ANG::BaseAccept)) : Array(ANG::AcceptMatch)
+  private def find_matches(headers : Array(HeaderType), priorities : Indexable(HeaderType)) : Array(ANG::AcceptMatch)
     matches = [] of ANG::AcceptMatch
 
     priorities.each_with_index do |priority, idx|

src/charset_negotiator.cr

@@ -1,8 +1,5 @@
 require "./abstract_negotiator"
 
 # A `ANG::AbstractNegotiator` implementation to negotiate `ANG::AcceptCharset` headers.
-class Athena::Negotiation::CharsetNegotiator < Athena::Negotiation::AbstractNegotiator
+class Athena::Negotiation::CharsetNegotiator < Athena::Negotiation::AbstractNegotiator(Athena::Negotiation::AcceptCharset)
-  private def create_header(header : String) : ANG::BaseAccept
-    ANG::AcceptCharset.new header
-  end
 end

src/encoding_negotiator.cr

@@ -1,8 +1,5 @@
 require "./abstract_negotiator"
 
 # A `ANG::AbstractNegotiator` implementation to negotiate `ANG::AcceptEncoding` headers.
-class Athena::Negotiation::EncodingNegotiator < Athena::Negotiation::AbstractNegotiator
+class Athena::Negotiation::EncodingNegotiator < Athena::Negotiation::AbstractNegotiator(Athena::Negotiation::AcceptEncoding)
-  private def create_header(header : String) : ANG::BaseAccept
-    ANG::AcceptEncoding.new header
-  end
 end

src/language_negotiator.cr

@@ -1,7 +1,7 @@
 require "./abstract_negotiator"
 
 # A `ANG::AbstractNegotiator` implementation to negotiate `ANG::AcceptLanguage` headers.
-class Athena::Negotiation::LanguageNegotiator < Athena::Negotiation::AbstractNegotiator
+class Athena::Negotiation::LanguageNegotiator < Athena::Negotiation::AbstractNegotiator(Athena::Negotiation::AcceptLanguage)
   protected def match(accept : ANG::AcceptLanguage, priority : ANG::AcceptLanguage, index : Int32) : ANG::AcceptMatch?
     accept_base = accept.language
     priority_base = priority.language
@@ -20,8 +20,4 @@ class Athena::Negotiation::LanguageNegotiator < Athena::Negotiation::AbstractNeg
 
     nil
   end
-
-  private def create_header(header : String) : ANG::BaseAccept
-    ANG::AcceptLanguage.new header
-  end
 end

src/negotiator.cr

@@ -1,7 +1,7 @@
 require "./abstract_negotiator"
 
 # A `ANG::AbstractNegotiator` implementation to negotiate `ANG::Accept` headers.
-class Athena::Negotiation::Negotiator < Athena::Negotiation::AbstractNegotiator
+class Athena::Negotiation::Negotiator < Athena::Negotiation::AbstractNegotiator(Athena::Negotiation::Accept)
   # TODO: Make this method less complex.
   #
   # ameba:disable Metrics/CyclomaticComplexity
@@ -63,8 +63,4 @@ class Athena::Negotiation::Negotiator < Athena::Negotiation::AbstractNegotiator
 
     sub_type.split '+', limit: 2
   end
-
-  private def create_header(header : String) : ANG::BaseAccept
-    ANG::Accept.new header
-  end
 end