#lang racket/base

(require net/url)

(provide input-prompt
         valid-http-or-file-url?
         )

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; goal   : Ask the user for input .
; pre    : p is a prompt.
; post   : It should give back the supplied input as string.
; result : the return value of until.
; internals:
;
; input-prompt displays the given prompt and reads a line
; of text. After the user presses enter, this line is
; fed to the until callback. If the until callback returns
; #f, the prompt is displayed again. Otherwise, the value
; of until is returned.
;
; The programmer must make sure the until returns whatever
; format is appropriate. In general it will be a string. 
;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

(define (input-prompt p #:loop-until [until (λ (x) x)])
  (let loop ()
    (display p)
    (flush-output)
    (let ((inp (read-line)))
      (let ((i (until inp)))
        (if i
            i
            (loop)))
      )
    )
  )


(define (valid-http-or-file-url? value)
  (if (not (string? value))
      #f
      (with-handlers ([exn:fail? (λ (exn) #f)])
        (let ((url (string->url value)))
          (and
           (member (url-scheme url) '("http" "https" "file"))
           (string? (url-host url))
           (not (string=? (url-host url) "")))))))