1 files changed, 118 insertions, 0 deletions
diff --git a/gems/gitlab-housekeeper/lib/gitlab/housekeeper/gitlab_client.rb b/gems/gitlab-housekeeper/lib/gitlab/housekeeper/gitlab_client.rb
new file mode 100644
index 00000000000..b28d44195cb
--- /dev/null
+++ b/gems/gitlab-housekeeper/lib/gitlab/housekeeper/gitlab_client.rb
@@ -0,0 +1,118 @@
+# frozen_string_literal: true
+
+require 'httparty'
+require 'json'
+
+module Gitlab
+  module Housekeeper
+    class GitlabClient
+      Error = Class.new(StandardError)
+
+      def initialize
+        @token = ENV.fetch("HOUSEKEEPER_GITLAB_API_TOKEN")
+        @base_uri = 'https://gitlab.com/api/v4'
+      end
+
+      def create_or_update_merge_request(
+        source_project_id:,
+        title:,
+        description:,
+        source_branch:,
+        target_branch:,
+        target_project_id:
+      )
+        existing_iid = get_existing_merge_request(
+          source_project_id: source_project_id,
+          source_branch: source_branch,
+          target_branch: target_branch,
+          target_project_id: target_project_id
+        )
+
+        if existing_iid
+          update_existing_merge_request(
+            existing_iid: existing_iid,
+            title: title,
+            description: description,
+            target_project_id: target_project_id
+          )
+        else
+          create_merge_request(
+            source_project_id: source_project_id,
+            title: title,
+            description: description,
+            source_branch: source_branch,
+            target_branch: target_branch,
+            target_project_id: target_project_id
+          )
+        end
+      end
+
+      private
+
+      def get_existing_merge_request(source_project_id:, source_branch:, target_branch:, target_project_id:)
+        response = HTTParty.get("#{@base_uri}/projects/#{target_project_id}/merge_requests",
+          query: {
+            state: :opened,
+            source_branch: source_branch,
+            target_branch: target_branch,
+            source_project_id: source_project_id
+          },
+          headers: {
+            'Private-Token' => @token
+          })
+
+        unless (200..299).cover?(response.code)
+          raise Error,
+            "Failed with response code: #{response.code} and body:\n#{response.body}"
+        end
+
+        data = JSON.parse(response.body)
+
+        return nil if data.empty?
+
+        iids = data.pluck('iid')
+
+        raise Error, "More than one matching MR exists: iids: #{iids.join(',')}" unless data.size == 1
+
+        iids.first
+      end
+
+      def create_merge_request(
+        source_project_id:, title:, description:, source_branch:, target_branch:,
+        target_project_id:)
+        response = HTTParty.post("#{@base_uri}/projects/#{source_project_id}/merge_requests", body: {
+          title: title,
+          description: description,
+          source_branch: source_branch,
+          target_branch: target_branch,
+          target_project_id: target_project_id
+        }.to_json,
+          headers: {
+            'Private-Token' => @token,
+            'Content-Type' => 'application/json'
+          })
+
+        return if (200..299).cover?(response.code)
+
+        raise Error,
+          "Failed with response code: #{response.code} and body:\n#{response.body}"
+      end
+
+      def update_existing_merge_request(existing_iid:, title:, description:, target_project_id:)
+        response = HTTParty.put("#{@base_uri}/projects/#{target_project_id}/merge_requests/#{existing_iid}", body: {
+          title: title,
+          description: description
+        }.to_json,
+          headers: {
+            'Private-Token' => @token,
+            'Content-Type' => 'application/json'
+          })
+
+        return if (200..299).cover?(response.code)
+
+        raise Error,
+          "Failed with response code: #{response.code} and body:\n#{response.body}"
+      end
+    end
+  end
+end