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 bits (* _size 8))
  
  (define/override (size . args) _size)

  (define-values (bound-min bound-max)
    ;; if a signed integer has n bits, it can contain a number between - (expt 2 (sub1 n)) and (sub1 (expt 2 (sub1 n)).
    (let* ([signed-max (sub1 (arithmetic-shift 1 (sub1 bits)))]
           [signed-min (sub1 (- signed-max))])
      (if _signed?
          (values signed-min signed-max)
          (values (- signed-min signed-min) (- signed-max signed-min)))))

  (define (unsigned->signed uint)
    (define most-significant-bit-mask (arithmetic-shift 1  (sub1 bits)))
    (- (bitwise-xor uint most-significant-bit-mask) most-significant-bit-mask))

  (define (signed->unsigned sint)
    (bitwise-and sint (arithmetic-shift 1 bits)))

  (define/augride (decode stream . args)
    (define bstr (send stream read _size))
    (define system-endian (if (system-big-endian?) 'be 'le))
    (define bs ((if (eq? endian system-endian) identity reverse) (bytes->list bstr)))
    (define unsigned-int (for/sum ([(b i) (in-indexed bs)])
                           (arithmetic-shift b (* 8 i))))
    ((if _signed? unsigned->signed identity) unsigned-int))

  (define/augride (encode stream val-in)
    (define val ((if (integer? val-in) inexact->exact identity) 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-values (bs _) (for/fold ([bs empty] [n val])
                                    ([i (in-range _size)])
                            (values (cons (bitwise-and n #xff) bs) (arithmetic-shift n -8))))
    (send stream write (apply bytes ((if (eq? endian 'be) identity reverse) bs)))))

(define-subclass* Number (Fixed size [fixed-endian (if (system-big-endian?) 'be 'le)] [fracBits (floor (/ size 2))])
  (super-make-object (string->symbol (format "int~a" size)) fixed-endian)
  (field [_point (expt 2 fracBits)])

  (define/override (decode stream . args)
    (define result (/ (super decode stream args) _point 1.0))
    (if (integer? result) (inexact->exact result) result))

  (define/override (encode stream val)
    (super encode stream (floor (* val _point)))))

(define fixed16 (+Fixed 16))
(define fixed16be (+Fixed 16 'be))
(define fixed16le (+Fixed 16 'le))
(define fixed32 (+Fixed 32))
(define fixed32be (+Fixed 32 'be))
(define fixed32le (+Fixed 32 'le))


(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)]
                 [(ID-CLASS ...) (prefix-id "Number:" #'(ID ...))])
    #'(begin (define+provide ID (let ([ID-CLASS (class Number (super-new))])
                                  (make-object ID-CLASS '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)

 (define es (+EncodeStream))
 (send fixed16be encode es 123.45)
 (check-equal? (send es dump) #"{s")
 (define ds (+DecodeStream (send es dump)))
 #;(check-equal? (ceiling (* (send fixed16be decode ds) 100)) 12345.0)

 (check-equal? (send int8 decode (bytes 127)) 127)
 (check-equal? (send int8 decode (bytes 255)) -1)

 (check-equal? (send int8 encode #f -1) (bytes 255))
 (check-equal? (send int8 encode #f 127) (bytes 127))


 )