;; JSON implementation for Scheme
;; See http://www.json.org/ or http://www.crockford.com/JSON/index.html
;;
;; Copyright (c) 2005 Tony Garnock-Jones <tonyg@kcbbs.gen.nz>
;; Copyright (c) 2005 LShift Ltd. <query@lshift.net>
;;
;; Permission is hereby granted, free of charge, to any person
;; obtaining a copy of this software and associated documentation
;; files (the "Software"), to deal in the Software without
;; restriction, including without limitation the rights to use, copy,
;; modify, merge, publish, distribute, sublicense, and/or sell copies
;; of the Software, and to permit persons to whom the Software is
;; furnished to do so, subject to the following conditions:
;;
;; The above copyright notice and this permission notice shall be
;; included in all copies or substantial portions of the Software.
;;
;; THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
;; EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
;; MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
;; NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
;; BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
;; ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
;; CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
;; SOFTWARE.

;; JSON Structures are represented as vectors: #((symbol . value) (symbol . value) ...)
;; JSON Arrays are lists
;;
#lang mzscheme

(require "packrat.ss")

(provide json-read
         json-write
         
         hashtable->vector
         vector->hashtable)

(define (hashtable->vector ht)
  (list->vector
   (hash-table-map ht cons)))

(define (vector->hashtable v)
  (let ((ht (make-hash-table)))
    (for-each (lambda (entry) (hash-table-put! ht (car entry) (cdr entry)))
              (vector->list v))
    ht))

(define json-write
  (let ()
    (define (write-ht vec p)
      (display "{" p)
      (do ((need-comma #f #t)
           (i 0 (+ i 1)))
        ((= i (vector-length vec)))
        (if need-comma
            (display ", " p)
            (set! need-comma #t))
        (let* ((entry (vector-ref vec i))
               (k (car entry))
               (v (cdr entry)))
          (cond
            ((symbol? k) (write (symbol->string k) p))
            ((string? k) (write k p)) ;; for convenience
            (else (error "Invalid JSON table key in json-write" k)))
          (display ": " p)
          (write-any v p)))
      (display "}" p))
    
    (define (write-array a p)
      (display "[" p)
      (let ((need-comma #f))
        (for-each (lambda (v)
                    (if need-comma
                        (display ", " p)
                        (set! need-comma #t))
                    (write-any v p))
                  a))
      (display "]" p))
    
    (define (write-any x p)
      (cond
        ((hash-table? x) (write-ht (hashtable->vector x) p))
        ((vector? x) (write-ht x p))
        ((pair? x) (write-array x p))
        ((symbol? x) (write (symbol->string x) p)) ;; for convenience
        ((or (string? x)
             (number? x)) (write x p))
        ((boolean? x) (display (if x "true" "false") p))
        ((void? x) (display "null" p))
        (else (error "Invalid JSON object in json-write" x))))
    
    (lambda (x . maybe-port)
      (write-any x (if (pair? maybe-port) (car maybe-port) (current-output-port))))))

(define json-read
  (let ()
    (define (generator p)
      (let ((ateof #f)
            (pos (top-parse-position "<?>")))
        (lambda ()
          (if ateof
              (values pos #f)
              (let ((x (read-char p)))
                (if (eof-object? x)
                    (begin
                      (set! ateof #t)
                      (values pos #f))
                    (let ((old-pos pos))
                      (set! pos (update-parse-position pos x))
                      (values old-pos (cons x x)))))))))
    
    (define parser
      (packrat-parser (begin
                        (define (white results)
                          (if (char-whitespace? (parse-results-token-value results))
                              (white (parse-results-next results))
                              (comment results)))
                        (define (skip-comment-char results)
                          (comment-body (parse-results-next results)))
                        (define (skip-to-newline results)
                          (if (memv (parse-results-token-value results) '(#\newline #\return))
                              (white results)
                              (skip-to-newline (parse-results-next results))))
                        (define (token str)
                          (lambda (starting-results)
                            (let loop ((pos 0) (results starting-results))
                              (if (= pos (string-length str))
                                  (make-result str results)
                                  (if (char=? (parse-results-token-value results) (string-ref str pos))
                                      (loop (+ pos 1) (parse-results-next results))
                                      (make-expected-result (parse-results-position starting-results) str))))))
                        (define (interpret-string-escape results k)
                          (let ((ch (parse-results-token-value results)))
                            (k (cond
                                 ((assv ch '((#\b . #\backspace)
                                             (#\n . #\newline)
                                             (#\f . #\page)
                                             (#\r . #\return)
                                             (#\t . #\tab))) => cdr) ;; we don't support the "u" escape for unicode
                                 (else ch))
                               (parse-results-next results))))
                        (define (jstring-body results)
                          (let loop ((acc '()) (results results))
                            (let ((ch (parse-results-token-value results)))
                              (case ch
                                ((#\\) (interpret-string-escape (parse-results-next results)
                                                                (lambda (val results)
                                                                  (loop (cons val acc) results))))
                                ((#\") (make-result (list->string (reverse acc)) results))
                                (else (loop (cons ch acc) (parse-results-next results)))))))
                        (define (jnumber-body starting-results)
                          (let loop ((acc '()) (results starting-results))
                            (let ((ch (parse-results-token-value results)))
                              (if (memv ch '(#\- #\+ #\0 #\1 #\2 #\3 #\4 #\5 #\6 #\7 #\8 #\9 #\. #\e #\E))
                                  (loop (cons ch acc) (parse-results-next results))
                                  (let ((n (string->number (list->string (reverse acc)))))
                                    (if n
                                        (make-result n results)
                                        (make-expected-result (parse-results-position starting-results) 'number)))))))
                        any)
                      (any ((white '#\{ entries <- table-entries white '#\}) (list->vector entries))
                           ((white '#\[ entries <- array-entries white '#\]) entries)
                           ((s <- jstring) s)
                           ((n <- jnumber) n)
                           ((white (token "true")) #t)
                           ((white (token "false")) #f)
                           ((white (token "null")) (void)))
                      (comment (((token "/*") b <- comment-body) b)
                               (((token "//") b <- skip-to-newline) b)
                               (() 'whitespace))
                      (comment-body (((token "*/") w <- white) w)
                                    ((skip-comment-char) 'skipped-comment-char))
                      (table-entries ((a <- table-entries-nonempty) a)
                                     (() '()))
                      (table-entries-nonempty ((entry <- table-entry white '#\, entries <- table-entries-nonempty) (cons entry entries))
                                              ((entry <- table-entry) (list entry)))
                      (table-entry ((key <- jstring white '#\: val <- any) (cons key val)))
                      (array-entries ((a <- array-entries-nonempty) a)
                                     (() '()))
                      (array-entries-nonempty ((entry <- any white '#\, entries <- array-entries-nonempty) (cons entry entries))
                                              ((entry <- any) (list entry)))
                      (jstring ((white '#\" body <- jstring-body '#\") body))
                      (jnumber ((white body <- jnumber-body) body))
                      ))
    
    (define (read-any p)
      (let ((result (parser (base-generator->results (generator p)))))
        (if (parse-result-successful? result)
            (parse-result-semantic-value result)
            (error "JSON Parse Error"
                   (let ((e (parse-result-error result)))
                     (list 'json-parse-error
                           (parse-position->string (parse-error-position e))
                           (parse-error-expected e)
                           (parse-error-messages e)))))))
    
    (lambda maybe-port
      (read-any (if (pair? maybe-port) (car maybe-port) (current-input-port))))))