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#lang restructure/racket
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(require "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 [len #f] [stream #f] [ctx #f])
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(unless stream (raise-argument-error 'LazyArray "stream" stream))
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(define starting-pos (· stream pos))
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(define item-cache (mhasheqv)) ; integer-keyed hash, rather than list
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(define/public-final (get index)
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(unless (<= 0 index (sub1 len))
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#;(raise-argument-error 'LazyArray:get (format "index in range 0 to ~a" len) index)
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(void))
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(ref! item-cache index (λ ()
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(define orig-pos (· stream pos))
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(send stream pos (+ starting-pos (* (send type size #f ctx) index)))
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(define new-item (send type decode stream ctx))
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(send stream pos orig-pos)
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new-item)))
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(define/public-final (to-list)
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(for/list ([i (in-range len)])
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(get i))))
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(define-subclass ArrayT (LazyArray)
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(inherit-field len type)
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(define/override (decode stream [parent #f])
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(define pos (· stream pos)) ; ! placement matters. `resolve-length` will change `pos`
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(define decoded-len (resolve-length len stream parent))
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(let ([parent (if (NumberT? len)
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(mhasheq 'parent parent
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'_startOffset pos
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'_currentOffset 0
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'_length len)
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parent)])
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(define res (+InnerLazyArray type decoded-len stream parent))
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(send stream pos (+ (· stream pos) (* decoded-len (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 to-list)
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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 to-list)
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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 to-list) '(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")) to-list) '(1 2 3 4)))
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