Add feature flags system with beacons flag for targeted rollout

.gitignore

@@ -43,3 +43,7 @@ db/structure.sql
 
 /app/assets/builds/*
 !/app/assets/builds/.keep
+
+# Ignore key files for decrypting credentials and more.
+/config/*.key
+

app/models/current.rb

@@ -1,5 +1,6 @@
 class Current < ActiveSupport::CurrentAttributes
   attribute :session
   attribute :beacon
+  attribute :feature_overrides
   delegate :user, to: :session, allow_nil: true
 end

app/models/feature_flags.rb

@@ -0,0 +1,62 @@
+module FeatureFlags
+  extend self
+
+  def enabled?(flag_name, user: nil)
+    override = Current.feature_overrides&.dig(flag_name.to_sym)
+    return override unless override.nil?
+
+    env_value = ENV["FEATURE_#{flag_name.to_s.upcase}"]
+    return cast_boolean(env_value) unless env_value.nil?
+
+    config = feature_config(flag_name)
+    return false if config.nil?
+    return cast_boolean(config) unless config.respond_to?(:dig)
+
+    return true if cast_boolean(config[:enabled])
+
+    user_allowed?(config, user)
+  end
+
+  def disabled?(flag_name, user: nil)
+    !enabled?(flag_name, user: user)
+  end
+
+  def enable!(flag_name)
+    (Current.feature_overrides ||= {})[flag_name.to_sym] = true
+  end
+
+  def disable!(flag_name)
+    (Current.feature_overrides ||= {})[flag_name.to_sym] = false
+  end
+
+  def with(flag_name, value)
+    old = Current.feature_overrides&.dig(flag_name.to_sym)
+    value ? enable!(flag_name) : disable!(flag_name)
+    yield
+  ensure
+    if old.nil?
+      Current.feature_overrides&.delete(flag_name.to_sym)
+    else
+      Current.feature_overrides[flag_name.to_sym] = old
+    end
+  end
+
+  private
+
+  def feature_config(flag_name)
+    Rails.application.credentials.dig(:features, flag_name.to_sym)
+  end
+
+  def user_allowed?(config, user)
+    return false if user.nil?
+
+    allowed_emails = config[:allowed_emails]
+    return false if allowed_emails.blank?
+
+    allowed_emails.include?(user.email)
+  end
+
+  def cast_boolean(value)
+    ActiveModel::Type::Boolean.new.cast(value) || false
+  end
+end

config/credentials.yml.enc

@@ -0,0 +1 @@
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--oKBd19vdWhjbzt0B--ppPQiT/cJjaOxgDtNZyU1A==

spec/models/feature_flags_spec.rb

@@ -0,0 +1,149 @@
+require "rails_helper"
+
+RSpec.describe FeatureFlags do
+  after { Current.feature_overrides = nil }
+
+  describe ".enabled?" do
+    context "with request-scoped override" do
+      it "returns true when flag is overridden to true" do
+        described_class.enable!(:beacons)
+
+        expect(described_class.enabled?(:beacons)).to be true
+      end
+
+      it "returns false when flag is overridden to false" do
+        described_class.disable!(:beacons)
+
+        expect(described_class.enabled?(:beacons)).to be false
+      end
+
+      it "takes precedence over credentials" do
+        allow(Rails.application.credentials).to receive(:dig)
+          .with(:features, :beacons).and_return(true)
+
+        described_class.disable!(:beacons)
+
+        expect(described_class.enabled?(:beacons)).to be false
+      end
+    end
+
+    context "with ENV override" do
+      it "returns true when ENV is set to true" do
+        allow(ENV).to receive(:[]).and_call_original
+        allow(ENV).to receive(:[]).with("FEATURE_BEACONS").and_return("true")
+
+        expect(described_class.enabled?(:beacons)).to be true
+      end
+
+      it "returns false when ENV is set to false" do
+        allow(ENV).to receive(:[]).and_call_original
+        allow(ENV).to receive(:[]).with("FEATURE_BEACONS").and_return("false")
+
+        expect(described_class.enabled?(:beacons)).to be false
+      end
+    end
+
+    context "with boolean credential" do
+      it "returns true when credential is true" do
+        allow(Rails.application.credentials).to receive(:dig)
+          .with(:features, :my_flag).and_return(true)
+
+        expect(described_class.enabled?(:my_flag)).to be true
+      end
+
+      it "returns false when credential is false" do
+        allow(Rails.application.credentials).to receive(:dig)
+          .with(:features, :my_flag).and_return(false)
+
+        expect(described_class.enabled?(:my_flag)).to be false
+      end
+    end
+
+    context "with hash credential and allowed_emails" do
+      before do
+        allow(Rails.application.credentials).to receive(:dig)
+          .with(:features, :beacons)
+          .and_return({ enabled: false, allowed_emails: [ "admin@skillrx.org" ] })
+      end
+
+      it "returns true for a user whose email is allowed" do
+        user = build(:user, email: "admin@skillrx.org")
+
+        expect(described_class.enabled?(:beacons, user: user)).to be true
+      end
+
+      it "returns false for a user whose email is not allowed" do
+        user = build(:user, email: "other@example.com")
+
+        expect(described_class.enabled?(:beacons, user: user)).to be false
+      end
+
+      it "returns false when no user is provided" do
+        expect(described_class.enabled?(:beacons)).to be false
+      end
+    end
+
+    context "with globally enabled hash credential" do
+      before do
+        allow(Rails.application.credentials).to receive(:dig)
+          .with(:features, :beacons)
+          .and_return({ enabled: true, allowed_emails: [ "admin@skillrx.org" ] })
+      end
+
+      it "returns true regardless of user" do
+        expect(described_class.enabled?(:beacons)).to be true
+      end
+    end
+
+    context "with unknown flag" do
+      it "returns false" do
+        allow(Rails.application.credentials).to receive(:dig)
+          .with(:features, :unknown).and_return(nil)
+
+        expect(described_class.enabled?(:unknown)).to be false
+      end
+    end
+  end
+
+  describe ".disabled?" do
+    it "returns the inverse of enabled?" do
+      allow(Rails.application.credentials).to receive(:dig)
+        .with(:features, :beacons).and_return(true)
+
+      expect(described_class.disabled?(:beacons)).to be false
+    end
+  end
+
+  describe ".with" do
+    it "enables the flag within the block" do
+      value_inside = nil
+
+      described_class.with(:beacons, true) do
+        value_inside = described_class.enabled?(:beacons)
+      end
+
+      expect(value_inside).to be true
+      expect(described_class.enabled?(:beacons)).to be false
+    end
+
+    it "disables the flag within the block" do
+      described_class.enable!(:beacons)
+
+      value_inside = nil
+      described_class.with(:beacons, false) do
+        value_inside = described_class.enabled?(:beacons)
+      end
+
+      expect(value_inside).to be false
+      expect(described_class.enabled?(:beacons)).to be true
+    end
+
+    it "restores the previous override after the block" do
+      described_class.enable!(:beacons)
+
+      described_class.with(:beacons, false) { }
+
+      expect(Current.feature_overrides[:beacons]).to be true
+    end
+  end
+end