1 files changed, 51 insertions, 0 deletions
diff --git a/app/finders/repositories/previous_tag_finder.rb b/app/finders/repositories/previous_tag_finder.rb
new file mode 100644
index 00000000000..150a6332c29
--- /dev/null
+++ b/app/finders/repositories/previous_tag_finder.rb
@@ -0,0 +1,51 @@
+# frozen_string_literal: true
+
+module Repositories
+  # A finder class for getting the tag of the last release before a given
+  # version.
+  #
+  # Imagine a project with the following tags:
+  #
+  # * v1.0.0
+  # * v1.1.0
+  # * v2.0.0
+  #
+  # If the version supplied is 2.1.0, the tag returned will be v2.0.0. And when
+  # the version is 1.1.1, or 1.2.0, the returned tag will be v1.1.0.
+  #
+  # This finder expects that all tags to consider meet the following
+  # requirements:
+  #
+  # * They start with the letter "v"
+  # * They use semantic versioning for the tag format
+  #
+  # Tags not meeting these requirements are ignored.
+  class PreviousTagFinder
+    TAG_REGEX = /\Av(?<version>#{Gitlab::Regex.unbounded_semver_regex})\z/.freeze
+
+    def initialize(project)
+      @project = project
+    end
+
+    def execute(new_version)
+      tags = {}
+      versions = [new_version]
+
+      @project.repository.tags.each do |tag|
+        matches = tag.name.match(TAG_REGEX)
+
+        next unless matches
+
+        version = matches[:version]
+        tags[version] = tag
+        versions << version
+      end
+
+      VersionSorter.sort!(versions)
+
+      index = versions.index(new_version)
+
+      tags[versions[index - 1]] if index&.positive?
+    end
+  end
+end