#lang scheme
  
  ; A blog is a (make-blog home posts)
  ; where home is a string, posts is a (listof post)
  (define-struct blog (home posts) #:mutable #:prefab)
  
  ; and post is a (make-post blog title body comments)
  ; where title is a string, body is a string,
  ; and comments is a (listof string)
  (define-struct post (title body comments) #:mutable #:prefab)
  
  ; initialize-blog! : path? -> blog
  ; Reads a blog from a path, if not present, returns default
  (define (initialize-blog! home)
    (local [(define (log-missing-exn-handler exn)
              (make-blog
               (path->string home)
               (list (make-post "First Post"
                                "This is my first post"
                                (list "First comment!"))
                     (make-post "Second Post"
                                "This is another post"
                                (list)))))
            (define the-blog
              (with-handlers ([exn? log-missing-exn-handler])
                (with-input-from-file home read)))]
      (set-blog-home! the-blog (path->string home))
      the-blog))
  
  ; save-blog! : blog -> void
  ; Saves the contents of a blog to its home
  (define (save-blog! a-blog)
    (local [(define (write-to-blog)
              (write a-blog))]
      (with-output-to-file (blog-home a-blog)
        write-to-blog
        #:exists 'replace)))
  
  ; blog-insert-post!: blog string string -> void
  ; Consumes a blog and a post, adds the post at the top of the blog.
  (define (blog-insert-post! a-blog title body)
    (set-blog-posts!
     a-blog
     (cons (make-post title body empty) (blog-posts a-blog)))
    (save-blog! a-blog))
  
  ; post-insert-comment!: blog post string -> void
  ; Consumes a blog, a post and a comment string.  As a side-efect,
  ; adds the comment to the bottom of the post's list of comments.
  (define (post-insert-comment! a-blog a-post a-comment)
    (set-post-comments!
     a-post
     (append (post-comments a-post) (list a-comment)))
    (save-blog! a-blog))
  
  (provide blog? blog-posts
           post? post-title post-body post-comments
           initialize-blog!
           blog-insert-post! post-insert-comment!)