(define-module (uniseg graphemes)
 #:use-module (ice-9 hash-table)
 #:use-module (srfi srfi-1)
 #:use-module (srfi srfi-9 gnu)
 #:export (make-grapheme
           grapheme?
           grapheme-width
           grapheme-delta-width
           grapheme-modification?
           grapheme-glyphs
           grapheme-glyphs-reverse
           grapheme-state
           grapheme-string))

(define-immutable-record-type <grapheme>
  (_make-grapheme width delta-width modification? state glyphs-reverse glyphs-promise string-promise)
  grapheme?
  (width grapheme-width)
  (delta-width grapheme-delta-width)
  (modification? grapheme-modification?)
  (state grapheme-state)
  (glyphs-reverse grapheme-glyphs-reverse)
  (glyphs-promise _grapheme-glyphs-promise)
  (string-promise _grapheme-string-promise))

(define (make-grapheme width delta modification? state glyphs-reverse)
  (_make-grapheme
   width
   delta
   modification?
   state
   glyphs-reverse
   (delay (reverse (glyphs-reverse)))
   (delay (reverse-list->string glyphs-reverse))))

(define (grapheme-glyphs grapheme)
  "Return a lazily-constructed list of glyphs in the grapheme"
  (force (_grapheme-glyphs-promise grapheme)))

(define (grapheme-string grapheme)
  "Return a lazily-constructed string of the glyphs in the grapheme."
  (force (_grapheme-string-promise grapheme)))