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#lang restructure/racket
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(require (prefix-in utils- "utils.rkt") "array.rkt" "number.rkt")
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(provide (all-defined-out))
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#|
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approximates
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https://github.com/mbutterick/restructure/blob/master/src/LazyArray.coffee
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|#
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(define-subclass object% (InnerLazyArray type [length_ #f] [stream #f] [ctx #f])
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(define base (and stream (· stream pos)))
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(define items (mhash)) ; rather than empty array
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(define/public-final (get index)
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(cond
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[(or (< index 0) (>= index length_)) #f]
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[else
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(define item (with-handlers ([exn:fail? (λ _ #f)])
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(ref items index)))
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(or item
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(let ()
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(define pos_ (· stream pos))
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(send stream pos (+ base (* (send type size #f ctx) index)))
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(define new-item (send type decode stream ctx))
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(ref-set! items index new-item)
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(send stream pos pos_)
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new-item))]))
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(define/public-final (toArray)
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(for/list ([i (in-range length_)])
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(get i)))
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(define/public-final (inspect)
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(format "~a" (toArray))))
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(define-subclass ArrayT (LazyArray)
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(inherit-field length_ type)
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(define/override (decode stream [parent #f])
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(define pos (· stream pos))
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(define length__ (utils-resolveLength length_ stream parent))
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(when (NumberT? length_)
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;; define hidden properties
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(set! parent (mhash 'parent parent
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'_startOffset pos
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'_currentOffset 0
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'_length length_)))
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(define res (+InnerLazyArray type length__ stream parent))
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(send stream pos (+ (· stream pos) (* length__ (send type size #f parent))))
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res)
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(define/override (size [val #f] [ctx #f])
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(super size (if (InnerLazyArray? val)
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(send val toArray)
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val) ctx))
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(define/override (encode stream val [ctx #f])
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(super encode stream (if (InnerLazyArray? val)
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(send val toArray)
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val) ctx)))
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#;(test-module
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(require "stream.rkt")
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(define bstr #"ABCD1234")
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(define ds (+DecodeStream bstr))
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(define la (+LazyArray uint8 4))
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(define ila (send la decode ds))
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(check-equal? (send ds pos) 4)
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(check-equal? (send ila get 1) 66)
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(check-equal? (send ila get 3) 68)
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(check-equal? (send ds pos) 4)
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(check-equal? (send ila toArray) '(65 66 67 68))
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(define la2 (+LazyArray int16be (λ (t) 4)))
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(define es (+EncodeStream))
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(send la2 encode es '(1 2 3 4))
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(check-equal? (send es dump) #"\0\1\0\2\0\3\0\4")
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(check-equal? (send (send la2 decode (+DecodeStream #"\0\1\0\2\0\3\0\4")) toArray) '(1 2 3 4))
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)
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