Language detection refactor (#2099)

* Extract detect_language to separate class

* Use default locale, not just en

* Add spec to confirm that whatlanguage cant identify empty string

* Allow account locale to override default in language detector

* PostStatusService supplies an account to detect language

spec/lib/language_detector_spec.rb

@@ -0,0 +1,71 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+describe LanguageDetector do
+  describe 'to_iso_s' do
+    it 'detects english language' do
+      string = 'Hello and welcome to mastadon'
+      result = described_class.new(string).to_iso_s
+
+      expect(result).to eq :en
+    end
+
+    it 'detects spanish language' do
+      string = 'Obtener un Hola y bienvenidos a Mastadon'
+      result = described_class.new(string).to_iso_s
+
+      expect(result).to eq :es
+    end
+
+    describe 'when language cant be detected' do
+      it 'confirm language engine cant detect' do
+        result = WhatLanguage.new(:all).language_iso('')
+        expect(result).to be_nil
+      end
+
+      describe 'with an account' do
+        it 'uses the account locale when present' do
+          user = double(:user, locale: 'fr')
+          account = double(:account, user: user)
+          result = described_class.new('', account).to_iso_s
+
+          expect(result).to eq :fr
+        end
+
+        it 'uses default locale when account is present but has no locale' do
+          user = double(:user, locale: nil)
+          account = double(:accunt, user: user)
+          result = described_class.new('', account).to_iso_s
+
+          expect(result).to eq :en
+        end
+      end
+
+      describe 'with an `en` default locale' do
+        it 'uses the default locale' do
+          string = ''
+          result = described_class.new(string).to_iso_s
+
+          expect(result).to eq :en
+        end
+      end
+
+      describe 'with a non-`en` default locale' do
+        around(:each) do |example|
+          before = I18n.default_locale
+          I18n.default_locale = :ja
+          example.run
+          I18n.default_locale = before
+        end
+
+        it 'uses the default locale' do
+          string = ''
+          result = described_class.new(string).to_iso_s
+
+          expect(result).to eq :ja
+        end
+      end
+    end
+  end
+end

spec/services/post_status_service_spec.rb

@@ -64,6 +64,18 @@ RSpec.describe PostStatusService do
     expect(status.application).to eq application
   end
 
+  it 'creates a status with a language set' do
+    detector = double(to_iso_s: :en)
+    allow(LanguageDetector).to receive(:new).and_return(detector)
+
+    account = Fabricate(:account)
+    text = 'test status text'
+
+    subject.call(account, text)
+
+    expect(LanguageDetector).to have_received(:new).with(text, account)
+  end
+
   it 'processes mentions' do
     mention_service = double(:process_mentions_service)
     allow(mention_service).to receive(:call)