Merge pull request #253 from MITLibraries/use-77-feature-flags

Initial Feature Flag system

Author: JPrevost

.gitignore

@@ -33,3 +33,4 @@ yarn-debug.log*
 
 .DS_Store
 .vscode/
+.yardoc

Gemfile

@@ -38,6 +38,7 @@ group :development do
   gem 'rubocop'
   gem 'rubocop-rails'
   gem 'web-console'
+  gem 'yard'
 end
 
 group :test do

Gemfile.lock

@@ -392,6 +392,7 @@ GEM
     websocket-extensions (0.1.5)
     xpath (3.2.0)
       nokogiri (~> 1.8)
+    yard (0.9.37)
     zeitwerk (2.7.3)
 
 PLATFORMS
@@ -443,6 +444,7 @@ DEPENDENCIES
   vcr
   web-console
   webmock
+  yard
 
 RUBY VERSION
    ruby 3.4.7p58

Makefile

@@ -0,0 +1,55 @@
+.PHONY: test
+
+help: # display Makefile commands
+	@awk 'BEGIN { FS = ":.*#"; print "Usage:  make <target>\n\nTargets:" } \
+  /^[-_[:alpha:]]+:.?*#/ { printf "  %-15s%s\n", $$1, $$2 }' $(MAKEFILE_LIST)
+
+#######################
+# Local development commands
+#######################
+
+run: # runs server on localhost
+	bin/rails server
+
+console: # runs console
+	bin/rails console
+
+test: # Run tests
+	bin/rails test
+
+coverage: test # Run tests and open coverage report in default web browser
+	open coverage/index.html
+
+#######################
+# Documentation commands
+#######################
+
+annotate: # update Rails models documentation header
+	bundle exec annotate --models
+
+docserver: # runs local documentation server
+	rm -rf .yardoc # Clears cache as it's sketchy af
+	yard server --reload
+
+#######################
+# Dependency commands
+#######################
+
+install: # Install dependencies
+	bundle install
+
+outdated: # List outdated dependencies
+	bundle outdated
+
+####################################
+# Code quality and safety commands
+####################################
+
+lint:
+	bundle exec rubocop
+
+lint-models:
+	bundle exec rubocop app/models
+
+lint-controllers:
+	bundle exec rubocop app/controllers

app/models/feature.rb

@@ -0,0 +1,49 @@
+# Central feature flag management class for the application. This class provides a simple,
+# centralized way to manage feature flags throughout the codebase.
+#
+# Feature flags are controlled through environment variables with the prefix 'FEATURE_'
+# followed by the uppercase feature name. Each flag defaults to false unless explicitly
+# enabled via environment variable to ensure consistency in how our features work.
+#
+# @example Basic Usage
+#   Feature.enabled?(:geodata)       # true if FEATURE_GEODATA=true in ENV
+#   Feature.enabled?(:unknown)       # Returns false for undefined features
+#
+# @example Setting Flags in Environment
+#   # In local ENV or Heroku config:
+#   FEATURE_GEODATA=true             # Enables the GDT feature
+#   FEATURE_BOOLEAN_PICKER=true      # Enables the boolean picker feature
+#
+#   # Any non-true value or not setting ENV does not enable the feature
+#   FEATURE_GEODATA=false            # Does not enable the GDT feature
+#   FEATURE_GEODATA=1                # Does not enable the GDT feature
+#   FEATURE_GEODATA=on               # Does not enable the GDT feature
+#
+# @example Usage in Different Contexts
+#   # In models/controllers:
+#   return unless Feature.enabled?(:geodata)
+#
+#   # In views:
+#   <% if Feature.enabled?(:geodata) %>
+#
+#   # In tests:
+#   ClimateControl.modify FEATURE_GEODATA: 'true' do
+#     assert Feature.enabled?(:geodata)
+#   end
+#
+class Feature
+  # List of all valid features in the application
+  VALID_FEATURES = %i[geodata boolean_picker].freeze
+
+  # Check if a feature is enabled by name
+  #
+  # @param feature_name [Symbol] The name of the feature to check
+  # @return [Boolean] true if the feature is enabled, false otherwise
+  # @example Check if a feature is enabled
+  #   Feature.enabled?(:geodata)
+  def self.enabled?(feature_name)
+    return false unless VALID_FEATURES.include?(feature_name)
+
+    ENV.fetch("FEATURE_#{feature_name.to_s.upcase}", false).to_s.downcase == 'true'
+  end
+end

test/models/feature_test.rb

@@ -0,0 +1,79 @@
+require 'test_helper'
+
+class FeatureTest < ActiveSupport::TestCase
+  test 'defined features default to false' do
+    refute Feature.enabled?(:geodata)
+    refute Feature.enabled?(:boolean_picker)
+  end
+
+  test 'undefined features return false' do
+    refute Feature.enabled?(:undefined_feature)
+  end
+
+  test 'features can be enabled via environment variables' do
+    ClimateControl.modify FEATURE_GEODATA: 'true' do
+      assert Feature.enabled?(:geodata)
+    end
+  end
+
+  test 'features can be disabled via environment variables' do
+    ClimateControl.modify FEATURE_GEODATA: 'false' do
+      refute Feature.enabled?(:geodata)
+    end
+  end
+
+  test 'environment variables are case insensitive' do
+    ClimateControl.modify FEATURE_GEODATA: 'TRUE' do
+      assert Feature.enabled?(:geodata)
+    end
+
+    ClimateControl.modify FEATURE_GEODATA: 'True' do
+      assert Feature.enabled?(:geodata)
+    end
+
+    ClimateControl.modify FEATURE_GEODATA: 'false' do
+      refute Feature.enabled?(:geodata)
+    end
+
+    ClimateControl.modify FEATURE_GEODATA: 'FALSE' do
+      refute Feature.enabled?(:geodata)
+    end
+  end
+
+  test 'non true boolean values default to false' do
+    ClimateControl.modify(
+      FEATURE_GEODATA: 'invalid'
+    ) do
+      refute Feature.enabled?(:geodata)
+    end
+
+    ClimateControl.modify(
+      FEATURE_GEODATA: '1'
+    ) do
+      refute Feature.enabled?(:geodata)
+    end
+
+    ClimateControl.modify(
+      FEATURE_GEODATA: 'yes'
+    ) do
+      refute Feature.enabled?(:geodata)
+    end
+  end
+
+  test 'feature names are case sensitive' do
+    ClimateControl.modify FEATURE_GEODATA: 'true' do
+      assert Feature.enabled?(:geodata)
+      refute Feature.enabled?(:GDT)
+    end
+  end
+
+  test 'multiple features can be controlled independently' do
+    ClimateControl.modify(
+      FEATURE_GEODATA: 'true',
+      FEATURE_BOOLEAN_PICKER: 'false'
+    ) do
+      assert Feature.enabled?(:geodata)
+      refute Feature.enabled?(:boolean_picker)
+    end
+  end
+end