1 files changed, 96 insertions, 0 deletions
diff --git a/app/services/groups/transfer_service.rb b/app/services/groups/transfer_service.rb
new file mode 100644
index 00000000000..e591c820cff
--- /dev/null
+++ b/app/services/groups/transfer_service.rb
@@ -0,0 +1,96 @@
+module Groups
+  class TransferService < Groups::BaseService
+    ERROR_MESSAGES = {
+      database_not_supported: 'Database is not supported.',
+      namespace_with_same_path: 'The parent group already has a subgroup with the same path.',
+      group_is_already_root: 'Group is already a root group.',
+      same_parent_as_current: 'Group is already associated to the parent group.',
+      invalid_policies: "You don't have enough permissions."
+    }.freeze
+
+    TransferError = Class.new(StandardError)
+
+    attr_reader :error
+
+    def initialize(group, user, params = {})
+      super
+      @error = nil
+    end
+
+    def execute(new_parent_group)
+      @new_parent_group = new_parent_group
+      ensure_allowed_transfer
+      proceed_to_transfer
+
+    rescue TransferError, ActiveRecord::RecordInvalid, Gitlab::UpdatePathError => e
+      @group.errors.clear
+      @error = "Transfer failed: " + e.message
+      false
+    end
+
+    private
+
+    def proceed_to_transfer
+      Group.transaction do
+        update_group_attributes
+      end
+    end
+
+    def ensure_allowed_transfer
+      raise_transfer_error(:group_is_already_root) if group_is_already_root?
+      raise_transfer_error(:database_not_supported) unless Group.supports_nested_groups?
+      raise_transfer_error(:same_parent_as_current) if same_parent?
+      raise_transfer_error(:invalid_policies) unless valid_policies?
+      raise_transfer_error(:namespace_with_same_path) if namespace_with_same_path?
+    end
+
+    def group_is_already_root?
+      !@new_parent_group && !@group.has_parent?
+    end
+
+    def same_parent?
+      @new_parent_group && @new_parent_group.id == @group.parent_id
+    end
+
+    def valid_policies?
+      return false unless can?(current_user, :admin_group, @group)
+
+      if @new_parent_group
+        can?(current_user, :create_subgroup, @new_parent_group)
+      else
+        can?(current_user, :create_group)
+      end
+    end
+
+    def namespace_with_same_path?
+      Namespace.exists?(path: @group.path, parent: @new_parent_group)
+    end
+
+    def update_group_attributes
+      if @new_parent_group && @new_parent_group.visibility_level < @group.visibility_level
+        update_children_and_projects_visibility
+        @group.visibility_level = @new_parent_group.visibility_level
+      end
+
+      @group.parent = @new_parent_group
+      @group.save!
+    end
+
+    def update_children_and_projects_visibility
+      descendants = @group.descendants.where("visibility_level > ?", @new_parent_group.visibility_level)
+
+      Group
+        .where(id: descendants.select(:id))
+        .update_all(visibility_level: @new_parent_group.visibility_level)
+
+      @group
+        .all_projects
+        .where("visibility_level > ?", @new_parent_group.visibility_level)
+        .update_all(visibility_level: @new_parent_group.visibility_level)
+    end
+
+    def raise_transfer_error(message)
+      raise TransferError, ERROR_MESSAGES[message]
+    end
+  end
+end