#lang scheme
(provide jvalue
         nothing nothing?
         jstring jstring?
         jnumber jnumber?
         jbool jbool?
         jnull jnull?
         jarray jarray?
         jobject jobject?
         is-null?
         get-string
         get-int
         get-bool
         get-double
         get-object
         get-array)

(define nothing 'nothing)
(define (nothing? x) (eq? x nothing))

(define-struct jvalue (type data))
(define (jtype-eq? value jtype) 
  (and (jvalue? value) 
       (eq? jtype (jvalue-type value))))

(define (jstring? value) (jtype-eq? value 'jstring))
(define (jstring value) 
  (if (string? value)
      (make-jvalue 'jstring value)
      (error "jstring expects type string : " value)))

(define (jnumber? value) (jtype-eq? value 'jnumber))
(define (jnumber value) 
  (if (number? value)
      (make-jvalue 'jnumber value)
      (error "jnumber expects type number : " value)))

(define (jbool? value) (jtype-eq? value 'jbool))
(define (jbool value) 
  (if (boolean? value)
      (make-jvalue 'jbool value)
      (error "jbool expects type boolean : " value)))

(define (jnull? value) (jtype-eq? value 'jnull))
(define (jnull) (make-jvalue 'jnull null))

(define (jobject? value) 
  (and (jtype-eq? value 'jobject)
       (andmap (hash-map (λ (k v) 
                           (and (string? k) (jvalue? v)))
                         (jvalue-data value)))))
(define (jobject value) 
  (if (hash? value)
      (make-jvalue 'jobject value)
      (error "jobject expects type hash : " value)))

(define (jarray? x) 
  (and (jtype-eq? x 'jarray) 
       (andmap jvalue? (jvalue-data x))))
(define (jarray value) 
  (if (list? value)
      (make-jvalue 'jarray value)
      (error "jobject expects type array : " value)))

(define (get-string value)
  (if (jstring? value)
      (jvalue-data value)
      nothing))

(define (get-int value)
  (if (jnumber? value)
      (truncate (jvalue-data value))
      nothing))

(define (get-double value)
  (if (jnumber? value)
      (jvalue-data value)
      nothing))

(define (get-bool value)
  (if (jbool? value)
      (jvalue-data value)
      nothing))

(define (get-object value)
  (if (jobject? value)
      (jvalue-data value)
      nothing))

(define (get-array value)
  (if (jarray? value)
      (jvalue-data value)
      nothing))

(define is-null? jnull?)