\version "2.19.38"

\pointAndClickOff

#(define (define-grob-property symbol type? description)
  (if (not (equal? (object-property symbol 'backend-doc) #f))
      (ly:error (_ "symbol ~S redefined") symbol))

  (set-object-property! symbol 'backend-type? type?)
  (set-object-property! symbol 'backend-doc description)
  symbol)

#(for-each
  (lambda (x)
    (apply define-grob-property x))
    `((tip 
      ,symbol? 
      "Which bracket tip should be printed for certain BarLines. 
Possible settings are @code{'up}, @code{'down} or @code{#f}
If set @code{#f} an automatic procedure takes over choosing the correct BarLine,
Which is not very safe.")))

CertainBracketTipsBarLines =
\override Score.BreakAlignGroup.after-line-breaking =
  #(lambda (grob)
    (let* ((elts (ly:grob-object grob 'elements))
           (bar-lines
             (if (null? elts)
                 '()
                 (filter 
                   (lambda (g) (grob::has-interface g 'bar-line-interface)) 
                   (ly:grob-array->list elts))))
           (possible-relevant-bar-lines
             (filter 
               (lambda (b) (not (null? (ly:grob-property b 'tip))))
               bar-lines)))
      (if (and (>= (length bar-lines) 2)
               (not (null? possible-relevant-bar-lines))
               (member 
                 (ly:grob-property (car bar-lines) 'glyph-name)
                 '(":..:" ":|." ".|:")))
          (let* ((possible-top-bar-lines 
                   (filter 
                     (lambda (b) (eq? (ly:grob-property b 'tip) 'up))
                     bar-lines))
                 (top-bar-lines
                   (if (null? possible-top-bar-lines)
                       (list (car bar-lines))
                       possible-top-bar-lines))
                 (bar-lines-list-length (length top-bar-lines))
                 (possible-bottom-bar-lines 
                   (filter 
                     (lambda (b) (eq? (ly:grob-property b 'tip) 'down))
                     bar-lines))
                 (bottom-bar-lines
                   (if (null? possible-bottom-bar-lines)
                       (list (last bar-lines))
                       possible-bottom-bar-lines))
                 (top-stil 
                   (ly:grob-property (car top-bar-lines) 'stencil))
                 (bottom-stil 
                   (ly:grob-property (car bottom-bar-lines) 'stencil))
                 (layout (ly:grob-layout grob))
                 (props 
                   (ly:grob-alist-chain 
                     grob 
                     (ly:output-def-lookup layout 'text-font-defaults)))
                 (font 
                   (ly:paper-get-font 
                     layout
                     (cons '((font-encoding . feta)) props)))
                 (tip (ly:font-get-glyph font "brackettips.up"))
                 (top-glyph-name 
                   (ly:grob-property (car top-bar-lines) 'glyph-name))
                 (repeat-type 
                   (cond ((string=? top-glyph-name  ":..:")
                          'double-repeat)
                         ((string=? top-glyph-name ":|.")
                          'close-repeat)
                         ((string=? top-glyph-name ".|:")
                          'open-repeat)
                         (else #f)))
                  (up-tip
                    (cond ((eq? repeat-type 'close-repeat)
                            (ly:stencil-translate-axis
                              (ly:stencil-scale tip -1 1)
                              (cdr (ly:stencil-extent top-stil X))
                              X))
                          ((eq? repeat-type 'double-repeat)
                            (let ((kern 
                                     (/ (ly:grob-property (car top-bar-lines) 
                                                          'kern) 
                                        10))
                                  (top-stil-ext (ly:stencil-extent top-stil X)))
                              (ly:stencil-translate-axis
                                (ly:stencil-combine-at-edge
                                  (ly:stencil-scale tip -1 1)
                                  X RIGHT
                                  tip
                                  kern)
                                (- (interval-center top-stil-ext) (/ kern 2))
                                X)))
                          (else tip)))
                  (down-tip (ly:stencil-scale up-tip 1 -1)))
            (for-each
              (lambda (grobb bar-stil dir tip-style)
                      (ly:grob-set-property! grobb 'stencil
                        (ly:stencil-combine-at-edge
                          bar-stil
                          Y
                          dir
                          tip-style
                          0)))
               (append top-bar-lines bottom-bar-lines)
               (append
                 (make-list bar-lines-list-length top-stil)
                 (make-list bar-lines-list-length bottom-stil))
               (append
                 (make-list bar-lines-list-length 1)
                 (make-list bar-lines-list-length -1))
               (append
                 (make-list bar-lines-list-length up-tip)
                 (make-list bar-lines-list-length down-tip)))))))
                 
%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% EXAMPLES
%%%%%%%%%%%%%%%%%%%%%%%%%%%

%% try different values
% #(set-global-staff-size 25)

%% for testing
%% http://lsr.di.unimi.it/LSR/Item?id=862
%% TODO
%% bug with BarNumbers and small \staffSize?
staffSize = #(define-music-function (parser location new-size) (number?)
  #{
    \set fontSize = #new-size
    \override StaffSymbol.staff-space = #(magstep new-size)
    \override StaffSymbol.thickness = #(magstep new-size)
  #})
  
\paper { indent = 0 }
                 
\layout {
  \context {
    \Score 
    \CertainBracketTipsBarLines
  }
}
    
mus =
#(make-sequential-music
  (map
    (lambda (s) 
      #{ 
      	 s1  \bar $s s1 \break \bar $s 
      #})
    '(":..:" ".|:" ":|.")))
       
\markup
  \rounded-box
  \fill-line {
  	  \pad-around #4
  	  "No Tips"
  }
    
\new StaffGroup
<<
  \new Staff \mus 
  \new Staff \mus 
  \new Staff \mus 
>>

\markup
  \rounded-box
  \fill-line {
  	  \pad-around #4
  	  \column {
  	    "Tips created automatic, using "
  	    "\\override BarLine.tip = #'auto"
  	    "Is this safe?"
  	  }
  }
    
\new StaffGroup
<<
  \new Staff 
    \with { \override BarLine.tip = #'auto } 
    \mus 
  \new Staff 
    \with { \override BarLine.tip = #'auto } 
    \mus 
  \new Staff 
    \with { \override BarLine.tip = #'auto } 
    \mus 
>>

\markup
  \rounded-box
  \fill-line {
  	  \pad-around #4
  	  \column {
  	    "Tips set by user, using "
  	    "\\override BarLine.tip = #'up"
  	    "or"
  	    "\\override BarLine.tip = #'down"
  	    "Every BarLine will get a tip according to the override"
  	  }
  }

<<
  \new StaffGroup
  <<
    \new Staff 
      \with { \override BarLine.tip = #'up \staffSize #3 }
      \mus
    \new Staff 
      \mus
    \new Staff 
      \with { \override BarLine.tip = #'down \staffSize #-3 }
      \mus
  >>
  
  \new StaffGroup
  <<
    \new Staff 
%      \with { \override BarLine.tip = #'up }
      \mus
    \new Staff 
      \mus
    \new Staff 
%      \with { \override BarLine.tip = #'down }
      \mus
  >>
>>