Get and Assign users & roles from/to a project

I need to copy the users and roles from a project to another. I’ve already done many similar activities such as copying versions/components/workflow scheme from a project to another. However getting into users and roles, I’ve looked into ProjectRoleAndActorStore, ProjectRoleManager and other provided objects but couldn’t perform or find any method that can help.
I’ve written a simple code that move ProjectRoles from a project to another without being sure of what it does actually, it compiled but I still didn’t get the users and roles in the new project am copying

This is what I’ve done so far:

	public void copyUsersRoles() {
		projectRoleAndActorStore = ComponentAccessor.getComponentOfType(ProjectRoleAndActorStore.class);
		Collection<ProjectRole> allProjectRoles = projectRoleAndActorStore.getAllProjectRoles();
		for(ProjectRole projectRole : allProjectRoles) {
			ProjectRoleActors sourceProjectRoleActors = 
					projectRoleManager.getProjectRoleActors(projectRole, sourceProject);
			ProjectRoleActors targetProjectRoleActors = 
					projectRoleManager.getProjectRoleActors(projectRole, targetProject);