(in-package #:json)

(defparameter number-literal
  (let ((signed-digits
          (comp ((sign (optional (one-of (unit #\-)
                                         (unit #\+))))
                 (natural (if sign
                            (crit (many (unit digit-char-p)))
                            (many (unit digit-char-p)))))
            (cons sign natural))))
    (comp ((base signed-digits)
           (dot (optional (unit #\.)))
           (fraction (if dot
                       (crit (many (unit digit-char-p)))
                       nothing))
           (e (optional (one-of (unit #\e) (unit #\E))))
           (exponent (if e
                       (crit signed-digits)
                       nothing)))
      (read-from-string
        (str:from-list
          (remove nil (append base (cons dot fraction) (cons (when e #\d) exponent))))))))

(defparameter string-literal
  (comp ((_ (unit #\"))
         (chars (optional (many (one-of (comp ((slash (unit #\\))
                                               (escaped (unit))
                                               (codepoints (if (char= escaped #\u)
                                                             (comp ((cp0 (unit digit-char-p))
                                                                    (cp1 (unit digit-char-p))
                                                                    (cp2 (unit digit-char-p))
                                                                    (cp3 (unit digit-char-p)))
                                                               (let ((str (make-string 7)))
                                                                 (setf (char str 0) #\#)
                                                                 (setf (char str 1) #\\)
                                                                 (setf (char str 2) #\u)
                                                                 (setf (char str 3) cp0)
                                                                 (setf (char str 4) cp1)
                                                                 (setf (char str 5) cp2)
                                                                 (setf (char str 6) cp3)
                                                                 str))
                                                             nothing)))
                                          (case escaped
                                            (#\n
                                             #\Newline)
                                            (#\t
                                             #\Tab)
                                            (#\u
                                             (read-from-string codepoints))
                                            (t escaped)))
                                        (unit (and (char/= it #\") (char/= it #\\)))))))
         (_ (crit (unit #\"))))
    (str:from-list chars)))

(defparameter true-symbol
  (comp ((_ (unit #\t))
         (_ (crit (literal "rue"))))
    'true))

(defparameter false-symbol
  (comp ((_ (unit #\f))
         (_ (crit (literal "alse"))))
    'false))

(defparameter null-symbol
  (comp ((_ (unit #\n))
         (_ (crit (literal "ull"))))
    'null))

(defvar json-value)

(defparameter json-array
  (comp ((_ (unit #\[))
         (vn (optional (separated-list json-value (unit #\,))))
         (_ (unit #\])))
    (apply #'vector vn)))

(defparameter json-object
  (let ((json-pair
          (comp ((_ whitespace)
                 (k string-literal)
                 (_ whitespace)
                 (_ (crit (unit #\:)))
                 (v (crit json-value)))
            (cons k v))))
    (comp ((_ (unit #\{))
           (vn (optional (separated-list json-pair (unit #\,))))
           (_ (unit #\})))
      (let* ((obj (make-hash-table :test #'equal :size (length vn))))
        (dolist (v vn)
          (setf (gethash (car v) obj) (cdr v)))
        obj))))

(defparameter json-value
  (comp ((_ whitespace)
         (v (one-of number-literal
                    string-literal
                    json-object
                    json-array
                    true-symbol
                    false-symbol
                    null-symbol))
         (_ whitespace))
    v))

(defun from-string (str)
  (run json-value (input:from-string str)))

(defun from-file (file)
  (run json-value (input:from-file file)))