(module fs-persist mzscheme
  (require (lib "file.ss")
           (lib "list.ss"))
  (require "fscache.ss")
  (provide read-path
           read-path/default
           write-path
           bind-to-file
           bind-within-directory)
  
  ;; Utility
  (define (dirname p)
    (apply build-path
           (reverse (rest (reverse (explode-path (build-path p)))))))
  
  ;; Caching
  (define cache (make-fscache))
  (define with-input-from-file/cache (make-with-input-from-file cache))
  (define with-output-to-file/cache (make-with-output-to-file cache))
  
  ;; Generators
  (define (read-path p)
    (with-input-from-file/cache p read))
  (define (read-path/default p fail-thunk)
    (with-handlers ([exn? (lambda (e) (fail-thunk))])
      (with-input-from-file/cache p read)))  
  (define (write-path p v)
    (make-directory* (dirname p))
    (with-output-to-file/cache p (lambda () (write v)) 'truncate))
  (define (bind-to-file path-f default-t)
    (values (lambda args
              (read-path/default
               (apply path-f args)
               default-t))
            (lambda args
              (define new (first (reverse args)))
              (define pargs (reverse (rest (reverse args))))
              (write-path
               (apply path-f pargs)
               new))))
  (define (bind-within-directory directory-fn)
    (define (item-dir . args)
      (define new (first (reverse args)))
      (define pargs (reverse (rest (reverse args))))
      (string-append (apply directory-fn pargs) new "/"))
    (values directory-fn
            (lambda args
              (map path->string 
                   (with-handlers ([exn? (lambda _ empty)])
                     (directory-list (apply directory-fn args)))))
            item-dir
            (lambda args
              (directory-exists? (apply item-dir args))))))