4 files changed, 124 insertions, 0 deletions
diff --git a/app/lib/translation_service.rb b/app/lib/translation_service.rb
new file mode 100644
index 000000000..526e26ae5
--- /dev/null
+++ b/app/lib/translation_service.rb
@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+class TranslationService
+  class Error < StandardError; end
+  class NotConfiguredError < Error; end
+  class TooManyRequestsError < Error; end
+  class QuotaExceededError < Error; end
+  class UnexpectedResponseError < Error; end
+
+  def self.configured
+    if ENV['DEEPL_API_KEY'].present?
+      TranslationService::DeepL.new(ENV.fetch('DEEPL_PLAN', 'free'), ENV['DEEPL_API_KEY'])
+    elsif ENV['LIBRE_TRANSLATE_ENDPOINT'].present?
+      TranslationService::LibreTranslate.new(ENV['LIBRE_TRANSLATE_ENDPOINT'], ENV['LIBRE_TRANSLATE_API_KEY'])
+    else
+      raise NotConfiguredError
+    end
+  end
+
+  def translate(_text, _source_language, _target_language)
+    raise NotImplementedError
+  end
+end
diff --git a/app/lib/translation_service/deepl.rb b/app/lib/translation_service/deepl.rb
new file mode 100644
index 000000000..89ccf01e5
--- /dev/null
+++ b/app/lib/translation_service/deepl.rb
@@ -0,0 +1,53 @@
+# frozen_string_literal: true
+
+class TranslationService::DeepL < TranslationService
+  include JsonLdHelper
+
+  def initialize(plan, api_key)
+    super()
+
+    @plan    = plan
+    @api_key = api_key
+  end
+
+  def translate(text, source_language, target_language)
+    request(text, source_language, target_language).perform do |res|
+      case res.code
+      when 429
+        raise TooManyRequestsError
+      when 456
+        raise QuotaExceededError
+      when 200...300
+        transform_response(res.body_with_limit)
+      else
+        raise UnexpectedResponseError
+      end
+    end
+  end
+
+  private
+
+  def request(text, source_language, target_language)
+    req = Request.new(:post, endpoint_url, form: { text: text, source_lang: source_language.upcase, target_lang: target_language, tag_handling: 'html' })
+    req.add_headers('Authorization': "DeepL-Auth-Key #{@api_key}")
+    req
+  end
+
+  def endpoint_url
+    if @plan == 'free'
+      'https://api-free.deepl.com/v2/translate'
+    else
+      'https://api.deepl.com/v2/translate'
+    end
+  end
+
+  def transform_response(str)
+    json = Oj.load(str, mode: :strict)
+
+    raise UnexpectedResponseError unless json.is_a?(Hash)
+
+    Translation.new(text: json.dig('translations', 0, 'text'), detected_source_language: json.dig('translations', 0, 'detected_source_language')&.downcase)
+  rescue Oj::ParseError
+    raise UnexpectedResponseError
+  end
+end
diff --git a/app/lib/translation_service/libre_translate.rb b/app/lib/translation_service/libre_translate.rb
new file mode 100644
index 000000000..66acdeed7
--- /dev/null
+++ b/app/lib/translation_service/libre_translate.rb
@@ -0,0 +1,43 @@
+# frozen_string_literal: true
+
+class TranslationService::LibreTranslate < TranslationService
+  def initialize(base_url, api_key)
+    super()
+
+    @base_url = base_url
+    @api_key  = api_key
+  end
+
+  def translate(text, source_language, target_language)
+    request(text, source_language, target_language).perform do |res|
+      case res.code
+      when 429
+        raise TooManyRequestsError
+      when 403
+        raise QuotaExceededError
+      when 200...300
+        transform_response(res.body_with_limit, source_language)
+      else
+        raise UnexpectedResponseError
+      end
+    end
+  end
+
+  private
+
+  def request(text, source_language, target_language)
+    req = Request.new(:post, "#{@base_url}/translate", body: Oj.dump(q: text, source: source_language, target: target_language, format: 'html', api_key: @api_key))
+    req.add_headers('Content-Type': 'application/json')
+    req
+  end
+
+  def transform_response(str, source_language)
+    json = Oj.load(str, mode: :strict)
+
+    raise UnexpectedResponseError unless json.is_a?(Hash)
+
+    Translation.new(text: json['translatedText'], detected_source_language: source_language)
+  rescue Oj::ParseError
+    raise UnexpectedResponseError
+  end
+end
diff --git a/app/lib/translation_service/translation.rb b/app/lib/translation_service/translation.rb
new file mode 100644
index 000000000..a55b82574
--- /dev/null
+++ b/app/lib/translation_service/translation.rb
@@ -0,0 +1,5 @@
+# frozen_string_literal: true
+
+class TranslationService::Translation < ActiveModelSerializers::Model
+  attributes :text, :detected_source_language
+end