(module picture-updater (lib "frtime.ss" "fta" "slideshow" "private" "frtime")
  
  (require (as-is:unchecked mzscheme make-hash-table hash-table-get hash-table-put!))
  
  (define master-table (make-hash-table))
  
  (define (track-var! name val)
    (hash-table-put! master-table name (new-cell val)))
  
  (define (track-events! name)
    (hash-table-put! master-table name (event-receiver)))
  
  (define-syntax track-rel-var!
    (syntax-rules ()
      [(_ name (id ...) expr)
       (begin
         (hash-table-put! master-table name (new-cell
                                             (let ([id (hash-table-get master-table 'id)] ...)
                                               expr)))
         #;(printf "~n~n relative var value: ~n~a~n~n" (let ([id (hash-table-get master-table 'id)] ...)
                                               expr)))]))
  
  (define (update-var! name val)
    (set-cell! (hash-table-get master-table name) val))
  
  (define (event-occur! name val)
    (send-event (hash-table-get master-table name) val))
  
  (define (call-when-change! name proc)
    (proc (value-now (hash-table-get master-table name)))
    (for-each-e! (changes (hash-table-get master-table name))
                 proc))
  
  (define (call-on-event! name proc)
    (for-each-e! (hash-table-get master-table name)
                 proc))
  
  (define-syntax with-var
    (syntax-rules ()
      [(_ ([let-name var-name] ...) body0 body1 ...)
       (let ([let-name (hash-table-get master-table var-name)] ...)
         body0
         body1 ...)]))
  
  (define (get-value-now name)
    (value-now/no-copy (hash-table-get master-table name)))
  
  (define (get-behavior name)
    (hash-table-get master-table name))
  
  (define (get-events name)
    (hash-table-get master-table name))
          
  
  (provide track-var!
           track-events!
           update-var!
           event-occur!
           call-when-change!
           call-on-event!
           ;track-rel-var!
           get-value-now
           get-behavior
           get-events
           ;with-var
           ))