\version "2.19.32"

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +thumb bracket

#(define (make-thumb-bracket-props location spec-str settings-alist) 
  (define (inchar? index) (> (string-length spec-str) index))
  (define (inchar  index) (string-ref spec-str index))
  (define (char->dir ch) 
   (case (char-upcase ch) ((#\R) 1) ((#\L) -1) (else 0))) 
  (define (char->digit ch)
   (if (char-numeric? ch) (- (char->integer ch) (char->integer #\0)) 0))
  (define (inhit->1 key-str) (if (string-contains spec-str key-str) 1 0))
  (define (get key) (assq-ref settings-alist key))
  (define (warn p1 p2) (ly:input-warning location 
   (_ " bad thumb-bracket:   ~a ~a~a~a") p1 "\"" p2 "\""))
  (let* ( ;% decode spec                                                                     
    (vdir            (if (inchar? 0) (char->dir   (inchar 0)) 0))
    (vbigger  (* 0.5 (if (inchar? 1) (char->digit (inchar 1)) 0)))
    (vfurther (* 0.5 (if (inchar? 2) (char->digit (inchar 2)) 0)))
    (hcloser  (* 0.5 (if (inchar? 3) (char->digit (inchar 3)) 0)))
    (hrear    (* 0.5 (if (inchar? 4) (char->digit (inchar 4)) 0)))
    (vbigger+ (* 5 (string-count spec-str #\|)))
    (posdir   ((if (string-contains spec-str "*") - +) vdir))
    (hcloser? (eq? (string-contains spec-str "!") #f))
    (vtip=?   (string-contains spec-str "="))
    (hdir-req (- (inhit->1 "]") (inhit->1 "[")))
    (closed? (char-lower-case? (inchar 0))))
   (if (zero? vdir) (begin (warn "first char in" spec-str) '())
   (let* ( ;% collect settings
    (hdir-init (get 'hdir-init))   (htip (get 'htip)) 
    (vtip (get (if vtip=? 'vtip= 'vtip)))  
    (vstem (get 'vstem))   (vmin (get 'vmin))   (hvernier (get 'hvernier))
    (vO 0) (hO 0) (hpad-base 0.5) ;% givens
    (hdir (if (zero? hdir-req) hdir-init hdir-req))
    (hflip? (positive? hdir))
    (h-interval 
     (if (positive? hdir) (cons hO (+ htip hrear)) (cons (- hrear) htip)))
    (vsize (+ vtip (if closed? vtip vstem) vbigger vbigger+))
    (vsize+ (if (and closed? (< vsize vmin)) (- vmin vsize) 0))
    (vshift (+ vfurther vtip (* 0.5 vsize+)))
    (bracket (lambda (grob) (let* ( ;% collect chord range from grob
      (vnote-lo-hi (ly:grob-property grob 'positions))
      (vnote ((if (eq? posdir 1) cdr car) vnote-lo-hi)))
     (grob-interpret-markup grob (markup #:translate (cons 
        ((if (positive? hdir) - +) hvernier) (- vnote (* vdir vshift)))
       #:combine #:draw-line (cons htip vO) #:combine 
        #:translate (cons hO (if closed? (* vdir (+ vsize vsize+)) vO))
         #:draw-line (cons htip vO)
        #:translate (cons (if (positive? hdir) htip hO) vO)
         #:draw-line (cons hO (* vdir (+ vsize vsize+)))))))))
    ;% alist of props for misusing Arpeggio as a thumb bracket
    `((stencil . ,bracket) 
      (X-extent . ,h-interval) 
      (padding . ,((if hcloser? - +) hpad-base hcloser)) 
      (direction . ,hdir) 
      (thickness . ,(get 'weight)))))))

thumbBracketEx = #(define-music-function 
  (spec settings) (string? list?)
 (let* (
   (props (make-thumb-bracket-props (*location*) spec settings)))
   (define (get key) (assq-ref props key))
  (if (null? props) #{ #} ;% abort without bracket
   #{
     \once \override Arpeggio.stencil   = #(get 'stencil)
     \once \override Arpeggio.X-extent  = #(get 'X-extent)
     \once \override Arpeggio.padding   = #(get 'padding)
     \once \override Arpeggio.direction = #(get 'direction) 
     \once \override Arpeggio.thickness = #(get 'thickness)
     $(make-music 'EventChord 'elements (list (make-music 'ArpeggioEvent)))
   #})))

thumbBracket = #(define-music-function (spec) (string?)
 (let ((settings thumbBracketSettings)) ;% as Defaults, or user defined
   ((ly:music-function-extract thumbBracketEx) spec settings)))

thumbBracketDefaults = #(quasiquote( 
  (hdir-init . ,LEFT) ;% usual placement wrt note: on RIGHT or LEFT
  (weight    . 1.5  ) ;% line thickness
  (htip      . 0.8  ) ;% horizontal length of bracket tip
  (vtip      . 0.75 ) ;% usual vertical overlap beyond notehead centre 
  (vtip=     . 0.30 ) ;% alternative vertical overlap 
  (vstem     . 1.25 ) ;% length of an unextended open bracket (excl. tip)
  (vmin      . 0.6  ) ;% minimum length of a closed bracket
  (hvernier  . 0.2  ) ;% horizontal quasi-extra-offset
  ))

thumbBracketSettings =  \thumbBracketDefaults
             
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -thumb bracket