#! /usr/bin/env /usr/local/bin/racket
#lang racket

(define (call-valid? call)
  (and
   (<= (string-length call) 9)
   (andmap
    (or/c char-numeric? char-alphabetic? (curry char=? #\-))
    (string->list call))))

(define (our-make-temporary-file [copy-from #f])
  ;; when deployed as a systemd socket, this program is expected to be
  ;; ran with PrivateTmp. however, in case this is not true, we still
  ;; make our own directory. "red", the restricted version of "ed",
  ;; has no facility for getting outside of the directory we start it
  ;; in.
  (make-temporary-file "red.~a"
                       #:copy-from copy-from
                       #:base-dir (make-temporary-directory)))

;; unfortunately, we cannot just exec red and let it take over the
;; I/O. ed, being the standard text editor, only works with standard
;; line endings, \n. telnet and BPQ, however, use \r\n. \r\n upsets
;; ed, the standard text editor.  so we need to wrap the input and
;; output ports ourselves in order to provide this translation.
(define (ed [path (our-make-temporary-file)])
  (match-define
    (list stdout stdin pid stderr proc)
    (parameterize ([current-directory (path-only path)])
      (process* "/usr/bin/red"
                "-p*"
                (path->string (file-name-from-path path))
                #:set-pwd? #t)))

  (define buffer (make-bytes 128))

  (define (loop)
    (let ([evt-result
           (sync
            (choice-evt (read-bytes-avail!-evt buffer stdout)
                        (read-line-evt (current-input-port) 'any)))])

      (cond
        ;; read-line-evt results in a string. we have something to write
        ;; on stdin.
        [(string? evt-result)
         (displayln evt-result stdin)
         (flush-output stdin)
         (loop)]

        ;; read-bytes-avail!-evt results in an integer. we have
        ;; something to read from stdout.
        [(integer? evt-result)
         (display (bytes->string/utf-8 (subbytes buffer 0 evt-result)))
         (flush-output)
         (loop)]

        ;; either event may EOF, which means that ed has died.
        [(eof-object? evt-result)

         ;; clean up
         (close-output-port stdin)
         (close-input-port stdout)
         (close-input-port stderr)
         (proc 'kill)

         path])))
  (loop))