Move the citation code out to a mixin: Citable.

This then auto-generates the `to_{format}` methods for each formatter
that has been registered.

Author: hainesr

lib/cff/citable.rb

@@ -0,0 +1,72 @@
+# frozen_string_literal: true
+
+# Copyright (c) 2018-2022 The Ruby Citation File Format Developers.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+require_relative 'formatters'
+
+##
+module CFF
+  # Methods to enable turning a CFF model or file into a citation.
+  #
+  # The core functionality is in the `citation` method. In addition, each
+  # available output format has a `to_{format}` method generated for it as
+  # well, e.g. `to_bibtex` or `to_apalike`. These methods take a single
+  # parameter, `preferred_citation:`, which defaults to `true` as in the
+  # `citation` method.
+  module Citable
+    # :call-seq:
+    #   citation(format, preferred_citation: true) -> String
+    #
+    # Output this Index in the specified format. Setting
+    # `preferred_citation: true` will honour the `preferred_citation` field in
+    # the index if one is present (default).
+    #
+    # `format` can be supplied as a String or a Symbol.
+    #
+    # Formats that are built-in to Ruby CFF are:
+    #
+    # * APAlike (e.g. `:apalike`, `'apalike'` or `'APAlike'`)
+    # * BibTeX (e.g. `:bibtex`, `'bibtex'` or `'BibTeX'`)
+    #
+    # *Note:* This method assumes that this Index is valid when called.
+    def citation(format, preferred_citation: true)
+      formatter = Formatters.formatter_for(format)
+      return '' if formatter.nil?
+
+      formatter.format(model: self, preferred_citation: preferred_citation)
+    end
+
+    def self.add_to_format_method(format) # :nodoc:
+      method = "to_#{format}"
+      return if method_defined?(method)
+
+      class_eval(
+        # def to_bibtex(preferred_citation: true)
+        #   citation(:bibtex, preferred_citation: preferred_citation)
+        # end
+        <<-END_TO_FORMAT, __FILE__, __LINE__ + 1
+          def #{method}(preferred_citation: true)
+            citation(:#{format}, preferred_citation: preferred_citation)
+          end
+        END_TO_FORMAT
+      )
+    end
+
+    # Add the formatters we know about already upfront.
+    Formatters.formatters.each do |format|
+      add_to_format_method(format)
+    end
+  end
+end

lib/cff/formatters.rb

@@ -20,20 +20,36 @@ module CFF
   module Formatters
     @formatters = {}
 
+    # :call-seq:
+    #   formatters -> Array
+    #
+    # Return the list of formatters that are available.
+    def self.formatters
+      @formatters.keys
+    end
+
     # :call-seq:
     #   register_formatter(class)
     #
     # Register a citation formatter. To be registered as a formatter, a
-    # class should at least provide:
+    # class should at least provide the following class methods:
     #
-    # * the constant `CITATION_FORMAT`, which should be a minimal descriptive
-    #   name for the format, e.g. `'BibTeX'`; and
-    # * the method `format`, which takes the to model to be formatted.
+    # * `format`, which takes the model to be formatted
+    # as a named parameter, and the option to cite a CFF file's
+    # `preferred-citation`:
+    # ```ruby
+    # def self.format(model:, preferred_citation: true); end
+    # ```
+    # * `label`, which returns a short name for the formatter, e.g.
+    # `'BibTeX'`. If your formatter class subclasses `CFF::Formatter`,
+    # then `label` is provided for you.
     def self.register_formatter(clazz)
       return unless clazz.singleton_methods.include?(:format)
       return if @formatters.has_value?(clazz)
 
-      @formatters[clazz.label.downcase.to_sym] = clazz
+      format = clazz.label.downcase.to_sym
+      @formatters[format] = clazz
+      Citable.add_to_format_method(format) if defined?(Citable)
     end
 
     def self.formatter_for(format) # :nodoc:

lib/cff/index.rb

@@ -23,7 +23,7 @@
 require_relative 'reference'
 require_relative 'schema'
 require_relative 'validatable'
-require_relative 'formatters'
+require_relative 'citable'
 
 require 'yaml'
 
@@ -56,6 +56,7 @@ module CFF
   # * `url`
   # * `version`
   class Index < ModelPart
+    include Citable
     include Licensable
     include Validatable
 
@@ -117,28 +118,6 @@ def self.open(index)
       cff
     end
 
-    # :call-seq:
-    #   citation(format, preferred_citation: true) -> String
-    #
-    # Output this Index in the specified format. Setting
-    # `preferred_citation: true` will honour the `preferred_citation` field in
-    # the index if one is present (default).
-    #
-    # `format` can be supplied as a String or a Symbol.
-    #
-    # Formats that are built-in to Ruby CFF are:
-    #
-    # * APAlike (e.g. `:apalike`, `'apalike'` or `'APAlike'`)
-    # * BibTeX (e.g. `:bibtex`, `'bibtex'` or `'BibTeX'`)
-    #
-    # *Note:* This method assumes that this Index is valid when called.
-    def citation(format, preferred_citation: true)
-      formatter = Formatters.formatter_for(format)
-      return '' if formatter.nil?
-
-      formatter.format(model: self, preferred_citation: preferred_citation)
-    end
-
     # :call-seq:
     #   type = type
     #
@@ -154,30 +133,6 @@ def to_yaml # :nodoc:
       YAML.dump fields, line_width: -1, indentation: 2
     end
 
-    # :call-seq:
-    #   to_apalike(preferred_citation: true) -> String
-    #
-    # Output this Index in an APA-like format. Setting
-    # `preferred_citation: true` will honour the `preferred_citation` field in
-    # the index if one is present (default).
-    #
-    # *Note:* This method assumes that this Index is valid when called.
-    def to_apalike(preferred_citation: true)
-      citation(:apalike, preferred_citation: preferred_citation)
-    end
-
-    # :call-seq:
-    #   to_bibtex(preferred_citation: true) -> String
-    #
-    # Output this Index in BibTeX format. Setting
-    # `preferred_citation: true` will honour the `preferred_citation` field in
-    # the index if one is present (default).
-    #
-    # *Note:* This method assumes that this Index is valid when called.
-    def to_bibtex(preferred_citation: true)
-      citation(:bibtex, preferred_citation: preferred_citation)
-    end
-
     private
 
     def fields

test/cff_citable_test.rb

@@ -0,0 +1,33 @@
+# frozen_string_literal: true
+
+# Copyright (c) 2018-2022 The Ruby Citation File Format Developers.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+require_relative 'test_helper'
+
+require 'cff/citable'
+
+class CFFCitableTest < Minitest::Test
+  def test_to_methods_present
+    methods = CFF::Citable.instance_methods
+
+    CFF::Formatters.formatters.each do |format|
+      # Depending on the order that tests are run, we may have an extra
+      # formatter hanging around.
+      next if format == :testformatterlabel
+
+      assert_includes(methods, "to_#{format}".to_sym)
+    end
+  end
+end