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

;; default directory used for storing dynamic application data
(define data-dir
  (build-path (find-system-path 'home-dir)
              (build-path ".local" "share" "palps")))

;; directory of the current user of the program
(define call-dir (make-parameter (string->path "/nobody")))

(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))

;; "main" procedure to be executed in an interactive context i.e. for
;; BPQ
(define (session-startup)
  (define call (string-downcase (read-line (current-input-port) 'any)))

  ;; something is seriously aswiss.
  (when (not (call-valid? call))
    (raise-user-error 'palps-session "invalid callsign"))

  ;; drop SSID, if there is one.
  (set! call (first (string-split call "-")))

  (parameterize ([call-dir (build-path data-dir call)])
    ;; at the moment, "being authorized" just means that the sysadmin
    ;; has granted a directory for that callsign.
    (when (not (directory-exists? (call-dir)))
      (displayln "sorry, but you are not an authorized user of the PALPS system")
      (displayln "visit https://gitea.farpn.net/w6vvn/palps for an explanation")
      (flush-output)

      (raise-user-error 'palps-session "unauthorized user"))

    (parameterize ([current-directory (call-dir)])
      (session))))

(define (session)
  (display "palps > ")
  (flush-output)

  (match (regexp-match #px"(\\w+)\\s*(.*)"
                       (read-line (current-input-port) 'any))
    [(list _ "ls" _)
     (for-each (λ (p) (displayln (path->string p)))
               (directory-list))
     (flush-output)]

    [(list _ "ed" name)
     (let ([path (build-path (current-directory)
                             (string->path-element name))])
       (let ([path (if (file-exists? path)
                       (ed (our-make-temporary-file path))
                       (ed))])
         (copy-file path name #:exists-ok? #t)))]

    [(list _ "rm" name)
     (let ([path (build-path (current-directory)
                             (string->path-element name))])
       (if (file-exists? path)
           (delete-file path)
           (displayln "file does not exist"))

       (flush-output))]

    [(or (list _ "bye" _)
         (list _ "b" _)
         (list _ "quit" _)
         (list _ "q" _))
     (displayln "goodbye")
     (flush-output)
     (exit)]

    [else
     (displayln "no such command")
     (flush-output)])

  (session))

(session-startup)