1 files changed, 102 insertions, 0 deletions
diff --git a/scripts/setup/find-jh-branch.rb b/scripts/setup/find-jh-branch.rb
new file mode 100755
index 00000000000..812e1c210f4
--- /dev/null
+++ b/scripts/setup/find-jh-branch.rb
@@ -0,0 +1,102 @@
+#!/usr/bin/env ruby
+# frozen_string_literal: true
+
+# In spec/scripts/setup/find_jh_branch_spec.rb we completely stub it
+require 'gitlab' unless Object.const_defined?(:Gitlab)
+
+require_relative '../api/default_options'
+
+class FindJhBranch
+  JH_DEFAULT_BRANCH = 'main-jh'
+  JH_PROJECT_PATH = 'gitlab-jh/gitlab'
+  BranchNotFound = Class.new(RuntimeError)
+
+  def run
+    return JH_DEFAULT_BRANCH unless merge_request?
+
+    jh_merge_request_ref_name ||
+      default_branch_merge_request_ref_name ||
+      stable_branch_merge_request_ref_name ||
+      default_branch_for_non_stable
+  end
+
+  private
+
+  def merge_request?
+    !!merge_request_id
+  end
+
+  def jh_merge_request_ref_name
+    branch_exist?(JH_PROJECT_PATH, jh_ref_name) && jh_ref_name
+  end
+
+  def default_branch_merge_request_ref_name
+    target_default_branch? && JH_DEFAULT_BRANCH
+  end
+
+  def stable_branch_merge_request_ref_name
+    target_stable_branch? && begin
+      jh_stable_branch_name = merge_request.target_branch.sub(/\-ee\z/, '-jh')
+
+      branch_exist?(JH_PROJECT_PATH, jh_stable_branch_name) &&
+        jh_stable_branch_name
+    end
+  end
+
+  def default_branch_for_non_stable
+    if target_stable_branch?
+      raise(BranchNotFound, "Cannot find a suitable JH branch")
+    else
+      JH_DEFAULT_BRANCH
+    end
+  end
+
+  def branch_exist?(project_path, branch_name)
+    !!gitlab.branch(project_path, branch_name)
+  rescue Gitlab::Error::NotFound
+    false
+  end
+
+  def target_default_branch?
+    merge_request.target_branch == default_branch
+  end
+
+  def target_stable_branch?
+    merge_request.target_branch.match?(/\A(?:\d+\-)+\d+\-stable\-ee\z/)
+  end
+
+  def ref_name
+    ENV['CI_COMMIT_REF_NAME']
+  end
+
+  def default_branch
+    ENV['CI_DEFAULT_BRANCH']
+  end
+
+  def merge_request_project_id
+    ENV['CI_MERGE_REQUEST_PROJECT_ID']
+  end
+
+  def merge_request_id
+    ENV['CI_MERGE_REQUEST_IID']
+  end
+
+  def jh_ref_name
+    "#{ref_name}-jh"
+  end
+
+  def merge_request
+    @merge_request ||= gitlab.merge_request(merge_request_project_id, merge_request_id)
+  end
+
+  def gitlab
+    @gitlab ||= Gitlab.client(
+      endpoint: API::DEFAULT_OPTIONS[:endpoint],
+      private_token: API::DEFAULT_OPTIONS[:api_token] || ''
+    )
+  end
+end
+
+if $0 == __FILE__
+  puts FindJhBranch.new.run
+end