%created by: ArnoldTheresius

#(define (Basic_graceecho_purger ctx)
  (let ((last-main-moment -1)
        (current-main-moment -1)
        (barline-found #f)
        (purge-barline #f)
        (last-barline-type '())
        (current-barline-type '())
        (metronomemark-found #f)
        (purge-metronomemark #f)
        (timesignature-found #f)
        (timesignature-style-got '())
        (timesignature-style-found '())
        (timesignature-fraction-found '())
        (purge-timesignature #f)
        (grobs-to-delete '()))
    `((acknowledgers
       (bar-line-interface ; BarLines and SpanBars
        . ,(lambda (trans grob source)
            (let
             ((keep-this-echo (ly:grob-property grob 'keep-grace-echo #f))
              (grob-name (grob::name grob)))
             (if (equal? (symbol->string grob-name) "BarLine")
              (let ((barline-symbol (ly:grob-property grob 'glyph '())))
               (if (not (null? barline-symbol))
                (if (and purge-barline
                         (not keep-this-echo)
                         (equal? last-barline-type barline-symbol))
                 (begin
                  (ly:grob-set-property! grob 'glyph '())
                  (ly:context-set-property! ctx 'forbidBreak #t))
                 (begin
                  (set! barline-found #t)
                  (set! current-barline-type barline-symbol))))))))
       ) ;; bar-line-interface
       (metronome-mark-interface
        . ,(lambda (trans grob source)
            (let ((keep-this-echo (ly:grob-property grob 'keep-grace-echo #f)))
             (if (and purge-metronomemark (not keep-this-echo))
              (set! grobs-to-delete (cons grob grobs-to-delete)) ;; aka a delayed ly:grob-suicide!
              (set! metronomemark-found #t))))
       ) ;; metronome-mark-interface
       (time-signature-interface
        . ,(lambda (trans grob source)
            (let ((keep-this-echo (ly:grob-property grob 'keep-grace-echo #f)))
             (if (and purge-timesignature
                      (not keep-this-echo)
                      (equal? timesignature-style-found (ly:grob-property grob 'style))
                      (equal? timesignature-fraction-found (ly:context-property ctx 'timeSignatureFraction)))
              (set! grobs-to-delete (cons grob grobs-to-delete)) ;; aka a delayed ly:grob-suicide!
              (begin
               (set! timesignature-style-got (ly:grob-property grob 'style))
               (set! timesignature-found #t)))))
       ) ;; time-signature-interface
      ) ;; acknowledgers
      (start-translation-timestep
       . ,(lambda (trans)
           (let*
            ((now-mom (ly:context-current-moment ctx))
             (now-main-mom (ly:moment-main now-mom)))  ;; function missing in 2.14.2 !
            (set! current-main-moment now-main-mom)
            (if (equal? last-main-moment now-main-mom)
             (begin
              (if barline-found (set! purge-barline #t))
              (if metronomemark-found (set! purge-metronomemark #t))
              (if timesignature-found (begin
                (set! timesignature-fraction-found (ly:context-property ctx 'timeSignatureFraction))
                (set! timesignature-style-found timesignature-style-got)
                (set! purge-timesignature #t))))
             (begin
              (set! barline-found #f)
              (set! purge-barline #f)
              (set! metronomemark-found #f)
              (set! purge-metronomemark #f)
              (set! timesignature-found #f)
              (set! purge-timesignature #f)))))
      ) ;; start-translation-timestep
      (stop-translation-timestep
       . ,(lambda (trans)
           (for-each ly:grob-suicide! grobs-to-delete)
           (set! grobs-to-delete '())
           (set! last-barline-type current-barline-type)
           (set! last-main-moment current-main-moment))
      ) ;; stop-translation-timestep
     )))

% uncomment this to enable it by default, not only
% if it's listed in the layout block of your scores.
%{
\layout {
  \context {
    \Score
    \consists #Basic_graceecho_purger
  }
}
%}

#(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))
    `((keep-grace-echo
      ,boolean? 
      "Do not purge this grob, it's wanted and not the result of a 'grace note 
echo' from different voices.")))

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%


Music = {
  % Test the keep-grace-echo property:
  % \once \override Score.MetronomeMark.keep-grace-echo = ##t
  \tempo "slow" 4 = 54
  \partial 4
  \tag #'Grace \acciaccatura b8 c'4
  \tag #'Grace \acciaccatura b8 c'1
  \repeat volta 2 {
    \tag #'Grace \acciaccatura b8 c'1
  }
  \tag #'Grace \acciaccatura b8 c'2
  \bar "|"
  \tag #'Grace \acciaccatura b8 c'2
  % Test the keep-grace-echo property:
  % \once \override Staff.TimeSignature.keep-grace-echo = ##t
  % \once \override Staff.BarLine.keep-grace-echo = ##t
  \bar "||"
  \time 3/4
  \tag #'Grace \acciaccatura b8 c'2.
  \bar "|."
}

% Test: do not purge bar line or time signature if not equal
Appendix = {
  \time 2/4 \grace { s128 \time 3/4 } e'2.
  \time 4/4 \grace { s128 \numericTimeSignature \time 4/4 } g'1
  \bar ";" \grace { s128 \bar "S-||" s128 \bar ".." } s128 \bar "|."
}


\score {
  \new StaffGroup <<
    \new Staff {
      \Music
      %Test_only: \Appendix
    }
    \new Staff {
      \removeWithTag #'Grace \Music
      %Text_only: \Appendix
    }
  >>
  \layout {
    \context { \Score
      \consists #Basic_graceecho_purger
    }
  }
}