public class PostServices : IPostServices
    {
        private const int PAGE_SIZE = 10;
        IPostRepository postRepository;

        public IList<Post> Recent(int pageNumber)
        {
            return this.postRepository.GetNewest(pageNumber, PAGE_SIZE);
        }

        public PostServices(IPostRepository postRepository)
        {
            this.postRepository = postRepository;
        }

        private bool postDoesNotExist(string url)
        {
            return postRepository.GetByID(url) != null && postRepository.GetByID(url).ID != null;
        }


        private string getUniqueUrl(Post post)
        {
            string url = post.Subject.ToUrl();

            if (postDoesNotExist(url))
                url += "-" + post.Owner.UserName;

            while (postDoesNotExist(url))
            {
                url += "-1";
            }
            return url;
        }

        public Post GetByID(string id)
        {
            return postRepository.GetByID(id);
        }

        public void Save(Post post)
        {
            if (String.IsNullOrEmpty(post.ID))
                post.ID = getUniqueUrl(post);
            postRepository.Save(post);
        }
    }