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#lang debug racket
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(require racket/class racket/match xenomorph sugar/unstable/dict)
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(provide CFFIndex)
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#|
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approximates
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https://github.com/mbutterick/fontkit/blob/master/src/cff/CFFIndex.js
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|#
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(define CFFIndex%
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(class x:base%
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(super-new)
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(init-field [(@type type) #f])
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(define (getCFFVersion ctx)
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(let loop ([ctx ctx])
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(cond
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[(and ctx (hash? ctx) (not (hash-ref ctx 'hdrSize #f)))
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(loop (hash-ref ctx 'x:parent))]
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[(and ctx (hash-ref ctx 'x:version #f))]
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[else -1])))
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(augride [@decode decode])
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(define (@decode stream parent)
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(match (decode (if (>= (getCFFVersion parent) 2) uint32be uint16be) stream)
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[0 null]
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[count (define offSize (decode uint8 stream))
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(define offsetType (match offSize
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[1 uint8]
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[2 uint16be]
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[3 uint24be]
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[4 uint32be]
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[_ (error 'bad-offset-size-in-CFFIndex)]))
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(define startPos (+ (pos stream) (* (add1 count) offSize) -1))
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(for/fold ([vals null]
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[start (send offsetType decode stream)]
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#:result (begin0 (reverse vals) (pos stream (+ startPos start))))
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([i (in-range count)])
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(define end (send offsetType decode stream))
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(define val
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(cond
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[@type
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(define apos (pos stream))
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(pos stream (+ startPos start))
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(hash-set! parent 'length (- end start))
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(begin0
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(send @type decode stream parent)
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(pos stream apos))]
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[else
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(hasheq 'offset (+ startPos start)
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'length (- end start))]))
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(values (cons val vals) end))]))
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(augride [@size size])
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(define (@size arr parent)
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(define size 2)
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(cond
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[(zero? (length arr)) size]
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[else
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(define type (or @type (x:buffer)))
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;; find maximum offset to determinine offset type
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(define offset 1)
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(for ([(item i) (in-indexed arr)])
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(set! offset (+ offset (send type size item parent))))
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(define offsetType
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(cond
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[(<= offset #xff) uint8]
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[(<= offset #xffff) uint16be]
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[(<= offset #xffffff) uint24be]
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[(<= offset #xffffffff) uint32be]
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[else (error 'CFFIndex-size (format "bad offset: ~a" offset))]))
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(set! size (+ size 1 (* (send offsetType size) (add1 (length arr)))))
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(set! size (+ size (sub1 offset)))
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size]))
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(define/augride (encode arr stream parent)
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#R arr
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(encode uint16be (length arr) stream)
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(cond
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[(zero? (length arr))]
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[else
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(define type (or @type (x:buffer)))
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;; find maximum offset to detminine offset type
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(define sizes null)
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(define offset 1)
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(for ([item (in-list arr)])
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(define s (send @type size item parent))
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(set! sizes (append sizes (list s)))
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(set! offset (+ offset s)))
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(define offsetType
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(cond
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[(<= offset #xff)
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uint8]
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[(<= offset #xffff)
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uint16]
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[(<= offset #xffffff)
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uint24]
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[(<= offset #xffffffff)
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uint32]
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[else
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(error 'cff-index-encode-bad-offset!)]))
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;; write offset size
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(encode uint8 (size offsetType) stream)
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;; write elements
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(set! offset 1)
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(encode offsetType offset stream)
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(for ([size (in-list sizes)])
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(set! offset (+ offset size))
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(encode offsetType offset stream))
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(for ([item (in-list arr)])
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(encode type item stream #:parent parent))]))))
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(define (CFFIndex [type #f])
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(new CFFIndex% [type type])) |