(use-modules (srfi srfi-1)
             (srfi srfi-13)
             (ice-9 binary-ports)
             (ice-9 textual-ports)
             (ice-9 format)
             (ice-9 regex)
             (rnrs bytevectors))

(define *host-passwd-file* (getenv "FUDO_HOST_PASSWD_FILE"))
(when (not *host-passwd-file*)
  (format #t (current-error-port "FUDO_HOST_PASSWD_FILE not set~%"))
  (exit 1))

(define *service-passwd-file* (getenv "FUDO_SERVICE_PASSWD_FILE"))
(when (not *service-passwd-file*)
  (format #t (current-error-port "FUDO_SERVICE_PASSWD_FILE not set~%"))
  (exit 1))

(define host-regex "^host-([a-zA-Z][a-zA-Z0-9_-]+)$")
(define service-regex "^service-([a-zA-Z][a-zA-Z0-9_-]+)$")

(define (make-verifier passwd-file)
  (let ((passwds (load passwd-file)))
    (lambda (username passwd)
      (and (> (string-length passwd) 6)
           (equal? (assoc-ref passwds username) passwd)))))

(define (make-authenticator host-verifier service-verifier)
  (lambda (username hostname password)
    (cond ((string-match host-regex username)
           (host-verifier (match:substring (string-match host-regex username) 1)
                          password))

          ((string-match service-regex username)
           (service-verifier (match:substring (string-match service-regex username) 1)
                             password))

          (else (begin (format #t "unrecognized username: ~s @ ~s~%" username hostname)
                nil)))))

(define (make-handler handlers)
  (lambda (request)
    (let ((op (assoc-ref handlers (first request))))
      (if op
          (apply op (cdr request))
          #f))))

(define (auth-listener handler)
  (let ((in (current-input-port))
        (out (current-output-port)))
    (while (not (eof-object? in))
           (let ((size (bytevector-u16-ref (get-bytevector-n in 2) 0 (endianness big)))
                 (response (make-bytevector 4 0)))
             (bytevector-u8-set! response 1 #x02)
             (if (handler (string-split (get-string-n in size) #\:))
                 (begin (bytevector-u8-set! response 3 #x01)
                        (put-bytevector out response 0 4)
                        (force-output out))
                 (begin (bytevector-u8-set! response 3 #x00)
                        (put-bytevector out response 0 4)
                        (force-output out)))))))

(auth-listener
 (make-handler
  (list (cons "auth"
              (make-authenticator (make-verifier *host-passwd-file*)
                                  (make-verifier *service-passwd-file*))))))