1 files changed, 68 insertions, 0 deletions
diff --git a/lib/gitlab/language_detection.rb b/lib/gitlab/language_detection.rb
new file mode 100644
index 00000000000..a41435fdb79
--- /dev/null
+++ b/lib/gitlab/language_detection.rb
@@ -0,0 +1,68 @@
+module Gitlab
+  class LanguageDetection
+    MAX_LANGUAGES = 5
+
+    def initialize(repository, repository_languages)
+      @repository = repository
+      @repository_languages = repository_languages
+    end
+
+    def languages
+      detection.keys
+    end
+
+    def language_color(name)
+      detection.dig(name, :color)
+    end
+
+    # Newly detected languages, returned in a structure accepted by
+    # Gitlab::Database.bulk_insert
+    def insertions(programming_languages)
+      lang_to_id = programming_languages.map { |p| [p.name, p.id] }.to_h
+
+      (languages - previous_language_names).map do |new_lang|
+        {
+          project_id: @repository.project.id,
+          share: detection[new_lang][:value],
+          programming_language_id: lang_to_id[new_lang]
+        }
+      end
+    end
+
+    # updates analyses which records only require updating of their share
+    def updates
+      to_update = @repository_languages.select do |lang|
+        detection.key?(lang.name) && detection[lang.name][:value] != lang.share
+      end
+
+      to_update.map do |lang|
+        { programming_language_id: lang.programming_language_id, share: detection[lang.name][:value] }
+      end
+    end
+
+    # Returns the ids of the programming languages that do not occur in the detection
+    # as current repository languages
+    def deletions
+      @repository_languages.map do |repo_lang|
+        next if detection.key?(repo_lang.name)
+
+        repo_lang.programming_language_id
+      end.compact
+    end
+
+    private
+
+    def previous_language_names
+      @previous_language_names ||= @repository_languages.map(&:name)
+    end
+
+    def detection
+      @detection ||=
+        @repository
+        .languages
+        .first(MAX_LANGUAGES)
+        .map { |l| [l[:label], l] }
+        .to_h
+    end
+  end
+end