#lang restructure/racket
(require "decodestream.rkt")

;; 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 (unsigned-type? type)
  (equal? "U" (substring (symbol->string type) 0 1)))

(test-module
 (check-true (unsigned-type? 'UInt16))
 (check-false (unsigned-type? 'Int16)))

(define-subclass BinaryIO% (NumberT type [endian (if (system-big-endian?) 'BE 'LE)])
  (getter-field [fn (format "~a~a" type (if (ends-with-8? type) "" endian))])

  (define/override (decode stream)
    (define bstr (read-bytes-exact (size) stream))
    (if (= 1 (size))
        (bytes-ref bstr 0)
        (integer-bytes->integer bstr (unsigned-type? type) (eq? endian 'BE))))

  (define/override (encode op val) 'foo)

  (define/override (size) (hash-ref TYPES type)))
    

(test-module
 (let ([o (make-object NumberT 'UInt16 'LE)]
       [ip (open-input-bytes (bytes 1 2 3 4))])
   (check-equal? (send o decode ip) 513) ;; 1000 0000  0100 0000
   (check-equal? (send o decode ip) 1027)) ;; 1100 0000 0010 0000

 (let ([o (make-object NumberT 'UInt16 'BE)]
       [ip (open-input-bytes (bytes 1 2 3 4))])
   (check-equal? (send o decode ip) 258) ;; 0100 0000 1000 0000 
   (check-equal? (send o decode ip) 772))) ;; 0010 0000 1100 0000 


(test-module
 (check-equal? (send (make-object NumberT 'UInt8) size) 1)
 (check-equal? (send (make-object NumberT 'UInt32) size) 4)
 (check-equal? (send (make-object NumberT 'Double) size) 8))