Added locale reducer

Necessary to provide a reusable function to process locales by dealing with the unnecessary duplication of locale key prefixes in the API responses. This will soon be used by the models.

Milestone: minor

lib/trmnl/api/locale_reducer.rb

@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+
+module TRMNL
+  module API
+    LocaleReducer = lambda do |attributes, prefix: "description-"|
+      attributes.each.with_object({}) do |(key, value), all|
+        next unless key.start_with? prefix
+
+        attributes.delete key
+        all[key.to_s.delete_prefix(prefix)] = value
+      end
+    end
+  end
+end

spec/lib/trmnl/api/locale_reducer_spec.rb

@@ -0,0 +1,40 @@
+# frozen_string_literal: true
+
+require "spec_helper"
+
+RSpec.describe TRMNL::API::LocaleReducer do
+  subject(:reducer) { described_class }
+
+  describe "#call" do
+    let :attributes do
+      {
+        name: "test",
+        "description-de": "german",
+        "description-fr": "french",
+        "description-en-GB": "united_kingdom"
+      }
+    end
+
+    it "answers locales hash" do
+      expect(reducer.call(attributes)).to eq(
+        "de" => "german",
+        "fr" => "french",
+        "en-GB" => "united_kingdom"
+      )
+    end
+
+    it "answers locales hash using custom prefix" do
+      attributes = {test_de: "german", test_fr: "french"}
+      expect(reducer.call(attributes, prefix: "test_")).to eq("de" => "german", "fr" => "french")
+    end
+
+    it "answers empty hash when there are no locales" do
+      expect(reducer.call({one: 1, two: 2})).to eq({})
+    end
+
+    it "mutates input when locales exist" do
+      original = attributes.dup
+      expect(reducer.call(attributes)).not_to eq(original)
+    end
+  end
+end