#lang racket/base
;; Sandbox management and use.

(require racket/match)
(require racket/sandbox)

(provide repl-shell)

(struct user-state (name master-sandbox master-namespace) #:transparent)

(define *user-states* (make-hash))

(define (get-user-state username)
  (when (not (hash-has-key? *user-states* username))
    (let* ((sb (make-evaluator 'racket/base))
	   (ns (call-in-sandbox-context sb current-namespace)))
      (hash-set! *user-states* username
		 (user-state username
			     sb
			     ns))))
  (hash-ref *user-states* username))

(define (repl-shell username in out)
  (match-define (user-state _ master-sandbox master-namespace) (get-user-state username))
  (parameterize ((current-input-port in)
		 (current-output-port out)
		 (current-error-port out)
		 (sandbox-input in)
		 (sandbox-output out)
		 (sandbox-error-output out)
		 (sandbox-memory-limit 2) ;; megabytes
		 (sandbox-eval-limits #f)
		 (sandbox-namespace-specs (list (lambda () master-namespace))))
    (printf "Hello, ~a.\n" username)
    (define slave-sandbox (make-evaluator '(begin)))
    ;; ^^ uses master-namespace via sandbox-namespace-specs
    (parameterize ((current-namespace master-namespace)
		   (current-eval slave-sandbox))
      (read-eval-print-loop))
    (fprintf out "\nGoodbye!\n")
    (kill-evaluator slave-sandbox)
    (close-input-port in)
    (close-output-port out)))