#lang racket

(define memory (make-vector 1024 #\nul))

(define flag (if (getenv "FLAG") (getenv "FLAG") "NO-FLAG-DEFINED"))

(define (write-to-memory! str memory-start-index)
  (define str-length (string-length str))
  (define (loop str-index)
    (when (< str-index str-length)
        (vector-set! memory (+ memory-start-index str-index) (string-ref str str-index))
        (loop (+ str-index 1))))
  (loop 0))

(define (init-memory!)
  (write-to-memory! "admin\0" 8)
  (write-to-memory! "does_not_matter\0" 14))

(init-memory!)

(define (read-from-memory memory-start-index)
  (define (loop str curr-index)
    (if (equal? (vector-ref memory curr-index) #\nul)
      str
      (loop (string-append str (string (vector-ref memory curr-index))) (+ curr-index 1))))
  (loop "" memory-start-index))

(define (find-in-memory value)
  (define (loop memory-index value-index)

    (cond
      ((>= memory-index (vector-length memory))
       #f)
      ((>= value-index (string-length value))
       (if (equal? (vector-ref memory memory-index) #\nul)
         (- memory-index (string-length value))
         (loop (+ memory-index 1) 0)))
      ((equal? (vector-ref memory memory-index) (string-ref value value-index))
       (loop (+ memory-index 1) (+ value-index 1)))
      (else
        (loop (+ memory-index 1) 0))))
  (loop 8 0))

(define (find-next-value-in-memory-after start-memory-index-previous)
  (define (loop memory-index)
    (if (equal? (vector-ref memory memory-index) #\nul)
      (+ memory-index 1)
      (loop (+ memory-index 1))))
  (loop start-memory-index-previous))

(define (get-password-for username)
  (define username-in-memory (find-in-memory username))
  (if username-in-memory
    (read-from-memory (find-next-value-in-memory-after username-in-memory))
    #f))

(define (receive-login-attempt-username username)
  (write-to-memory! username 0))

(define (passwords-match? received-password)
  (define login-username (read-from-memory 0))
  (define password-in-memory (get-password-for login-username))
  (equal? received-password password-in-memory))

(define (accept-null-termination str)
  (string-replace str "\\0" "\0"))

(define (main)
  (display "username: " (current-output-port))
  (receive-login-attempt-username (accept-null-termination (read-line (current-input-port) 'any)))
  (display "password: " (current-output-port))
  (define password (read-line (current-input-port) 'any))
  (if (passwords-match? password)
    (display (string-append "Superduper dokaboka bolegismo secret flag: " flag " :)") (current-output-port))
    (display "Incorrect password!!!1!! >:(" (current-output-port))))

(main)