#lang scheme/base
(require htdp/error)

(provide string->integer-list
         integer-list->string
         file->string write-string-to-file)

(define (string->integer-list s)
  (check-arg 'string->integer-list (string? s) s "string" 0)
  (map char->integer (string->list s)))

(define (scalar-value? n)
  (or (<= 0 n 55295)
      (<= 57344 n 1114111)))

(define (integer-list->string lis)
  (check-arg 'integer-list->string
	     (and (list? lis)
		  (andmap integer? lis)
		  (andmap scalar-value? lis))
             lis "list of scalar values" 0)
  (list->string (map integer->char lis)))

(define (file->string filename)
  (check-arg 'file->string
             (string? filename) filename "file name" 0)
  (call-with-input-file filename
    (lambda (port)
      (let loop ((rev '()))
        (let ((s (read-string 4096 port)))
          (cond
            ((eof-object? s)
             (apply string-append (reverse rev)))
            ((<= (string-length s) 4096)
             (apply string-append (reverse (cons s rev))))
            (loop (cons s rev))))))))

(define (write-string-to-file string filename)
  (check-arg 'write-string-to-file
             (string? string) string "string" 0)
  (check-arg 'write-string-to-file
             (string? filename) filename "file name" 1)
  (call-with-output-file filename
    (lambda (port)
      (display string port))
    #:exists 'replace))