typesetting/pitfall/restructure/number.rkt

#lang restructure/racket
(require "stream.rkt" "sizes.rkt" (for-syntax "sizes.rkt" racket/match))
(provide (all-defined-out))

#|
approximates
https://github.com/mbutterick/restructure/blob/master/src/Number.coffee
|#

(define (ends-with-8? type)
  (define str (symbol->string type))
  (equal? (substring str (sub1 (string-length str))) "8"))

(define (signed-type? type)
  (not (equal? "u" (substring (symbol->string type) 0 1))))

(test-module
 (check-false (signed-type? 'uint16))
 (check-true (signed-type? 'int16)))

(define-subclass Streamcoder (Number [type 'uint16] [endian (if (system-big-endian?) 'be 'le)])
  
  (getter-field [number-type (string->symbol (format "~a~a" type (if (ends-with-8? type) "" endian)))])
  (define _signed? (signed-type? type))

  ;; `get-type-size` will raise error if number-type is invalid: use this as check of input
  ;; size of a number doesn't change, so we can stash it as `_size`
  (define _size (with-handlers ([exn:fail:contract?
                                 (λ (exn) 
                                   (raise-argument-error 'Number "valid type and endian" (format "~v ~v" type endian)))])
                  (get-type-size number-type)))
  
  (define/override (size . args) _size)

  (define-values (bound-min bound-max)
    (let* ([signed-max (sub1 (expt 2 (sub1 (* _size 8))))]
           [signed-min (sub1 (- signed-max))])
      (if _signed?
          (values signed-min signed-max)
          (values (- signed-min signed-min) (- signed-max signed-min)))))

  (define/augment (decode stream . args)
    (define bstr (send stream read _size))
    (if (= 1 _size)
        (+ (bytes-ref bstr 0) (if _signed? bound-min 0))
        (integer-bytes->integer bstr _signed? (eq? endian 'be))))

  (define/augment (encode stream val-in)
    (define val (if (integer? val-in) (inexact->exact val-in) val-in))
    ;; todo: better bounds checking
    (unless (<= bound-min val bound-max)
      (raise-argument-error 'Number:encode (format "value within range of ~a ~a-byte int (~a to ~a)" (if _signed? "signed" "unsigned") _size bound-min bound-max) val))
    (define bstr (if (= 1 _size)
                     (bytes (- val (if _signed? bound-min 0)))
                     (integer->integer-bytes val _size _signed? (eq? endian 'be))))
    (send stream write bstr)))
    

(test-module
 (check-exn exn:fail:contract? (λ () (+Number 'not-a-valid-type)))
 (check-exn exn:fail:contract? (λ () (send uint8 encode (+EncodeStream) 256)))
 (check-not-exn (λ () (send uint8 encode (+EncodeStream) 255)))
 (check-exn exn:fail:contract? (λ () (send int8 encode (+EncodeStream) 256)))
 (check-exn exn:fail:contract? (λ () (send int8 encode (+EncodeStream) 255)))
 (check-not-exn (λ () (send int8 encode (+EncodeStream) 127)))
 (check-not-exn (λ () (send int8 encode (+EncodeStream) -128)))
 (check-exn exn:fail:contract? (λ () (send int8 encode (+EncodeStream) -129)))
 (check-exn exn:fail:contract? (λ () (send uint16 encode (+EncodeStream) (add1 #xffff))))
 (check-not-exn (λ () (send uint16 encode (+EncodeStream) #xffff)))
 
 (let ([o (+Number 'uint16 'le)]
       [ip (+DecodeStream (bytes 1 2 3 4))]
       [op (open-output-bytes)])
   (check-equal? (send o decode ip) 513) ;; 1000 0000  0100 0000
   (check-equal? (send o decode ip) 1027)  ;; 1100 0000 0010 0000
   (send o encode op 513)
   (check-equal? (get-output-bytes op) (bytes 1 2))
   (send o encode op 1027)
   (check-equal? (get-output-bytes op) (bytes 1 2 3 4)))

 (let ([o (+Number 'uint16 'be)]
       [ip (+DecodeStream (bytes 1 2 3 4))]
       [op (open-output-bytes)])
   (check-equal? (send o decode ip) 258) ;; 0100 0000 1000 0000 
   (check-equal? (send o decode ip) 772) ;; 0010 0000 1100 0000
   (send o encode op 258)
   (check-equal? (get-output-bytes op) (bytes 1 2))
   (send o encode op 772)
   (check-equal? (get-output-bytes op) (bytes 1 2 3 4))))


(test-module
 (check-equal? (send (+Number 'uint8) size) 1)
 (check-equal? (send (+Number) size) 2)
 (check-equal? (send (+Number 'uint32) size) 4)
 (check-equal? (send (+Number 'double) size) 8))


;; use keys of type-sizes hash to generate corresponding number definitions
(define-macro (make-int-types)
  (with-pattern ([((ID BASE ENDIAN) ...) (for/list ([k (in-hash-keys type-sizes)])
                                                   (define kstr (format "~a" k))
                                                   (match-define (list* prefix suffix _)
                                                     (regexp-split #rx"(?=[bl]e|$)" kstr))
                                                   (map string->symbol
                                                        (list (string-downcase kstr)
                                                              prefix
                                                              (if (positive? (string-length suffix))
                                                                  suffix
                                                                  (if (system-big-endian?) "be" "le")))))]
                 [(ID ...) (suffix-id #'(ID ...) #:context caller-stx)])
                #'(begin (define+provide ID (make-object Number 'BASE 'ENDIAN)) ...)))
                                                            
(make-int-types)

(test-module
 (check-equal? (send uint8 size) 1)
 (check-equal? (send uint16 size) 2)
 (check-equal? (send uint32 size) 4)
 (check-equal? (send double size) 8))