\version "2.19.21"

%{
    Print key signatures for transcriptions of early music in 
    which hard and soft hexachords are juxtaposed.  In other 
    words, in the absence of accidentals, B is natural or flat
    depending on its octave.

    Acknowledgments to:
    * Urs Liska 
    (http://lilypondblog.org/2014/03/music-functions-2-start-doing-something-useful/)
    for drawing my attention to \temporary \override ... \revert.
    * Pierre Perol-Schneider 
    (http://lists.gnu.org/archive/html/lilypond-user/2014-11/msg00454.html)
    for the lambda function on which this code is based.

    To do: 
    * This code is ripe for refactoring, but might be 
    easier to read in its present form.  If refactored,
    the interface could be something like:
    \keysigBfaBmi "clef" "upperB" "lowerB" { ...music... }
      where: clef   := treble | bass
             upperB := natural | flat
             lowerB := natural | flat
    * Add some error-checking.
%}

keysigBfaBmiTreble = 
  #(define-music-function (P L my-music)
                          (ly:music?)
    #{
      \set Staff.keyAlterations = #`(((-1 . 6) . ,NATURAL)
                                     (( 0 . 6) . ,FLAT))
      \set Staff.printKeyCancellation = ##f 
      \temporary \override Staff.KeySignature.stencil =
      #(lambda (grob) (grob-interpret-markup grob
                      #{
                        \markup
                        \translate #'(0 . -3.5) {
                        \combine 
                        \translate #'(0 . 3.5)  
                        \musicglyph #"accidentals.flat"
                          \combine
                          \translate #'(-.4 . .5)
                          \override #'(thickness . 2)
                          \draw-line #'(1.5 . 0)
                          \musicglyph #"accidentals.natural"
                        }
                      #}))
    #my-music
    \revert Staff.KeySignature.stencil
    #}
  )

keysigBfaBmiBass = 
  #(define-music-function (P L my-music)
                          (ly:music?)
    #{
      \set Staff.keyAlterations = #`(((-2 . 6) . ,FLAT)
                                     (( -1 . 6) . ,NATURAL))
      \set Staff.printKeyCancellation = ##f 
      \temporary \override Staff.KeySignature.stencil =
      #(lambda (grob) (grob-interpret-markup grob
                      #{
                        \markup
                        {
                        \combine 
                        \translate #'(0 . -1)  
                        \musicglyph #"accidentals.flat"
                        \translate #'(0 . 2.5)
                        \musicglyph #"accidentals.natural"
                        }
                      #}))
    #my-music
    \revert Staff.KeySignature.stencil
    #}
  )

keysigBfaBfaTreble = 
  #(define-music-function (P L my-music)
                          (ly:music?)
    #{
      \set Staff.keyAlterations = #`(((-1 . 6) . ,FLAT)
                                     (( 0 . 6) . ,FLAT))
      \set Staff.printKeyCancellation = ##f 
      \temporary \override Staff.KeySignature.stencil =
      #(lambda (grob) (grob-interpret-markup grob
                      #{
                        \markup
                        \translate #'(0 . -3.5) {
                        \combine 
                        \translate #'(0 . 3.5)  
                        \musicglyph #"accidentals.flat"
                          \combine
                          \translate #'(-.4 . .5)
                          \override #'(thickness . 2)
                          \draw-line #'(1.5 . 0)
                          \musicglyph #"accidentals.flat"
                        }
                      #}))
    #my-music
    \revert Staff.KeySignature.stencil
    #}
  )

keysigBfaBfaBass = 
  #(define-music-function (P L my-music)
                          (ly:music?)
    #{
      \set Staff.keyAlterations = #`(((-2 . 6) . ,FLAT)
                                     (( -1 . 6) . ,FLAT))
      \set Staff.printKeyCancellation = ##f 
      \temporary \override Staff.KeySignature.stencil =
      #(lambda (grob) (grob-interpret-markup grob
                      #{
                        \markup
                        {
                        \combine 
                        \translate #'(0 . -1)  
                        \musicglyph #"accidentals.flat"
                        \translate #'(0 . 2.5)
                        \musicglyph #"accidentals.flat"
                        }
                      #}))
    #my-music
    \revert Staff.KeySignature.stencil
    #}
  )

keysigBmiBmiTreble = 
  #(define-music-function (P L my-music)
                          (ly:music?)
    #{
      \set Staff.keyAlterations = #`(((-1 . 6) . ,NATURAL)
                                     (( 0 . 6) . ,NATURAL))
      \set Staff.printKeyCancellation = ##f 
      \temporary \override Staff.KeySignature.stencil =
      #(lambda (grob) (grob-interpret-markup grob
                      #{
                        \markup
                        \translate #'(0 . -3.5) {
                        \combine 
                        \translate #'(0 . 3.5)  
                        \musicglyph #"accidentals.natural"
                          \combine
                          \translate #'(-.4 . .5)
                          \override #'(thickness . 2)
                          \draw-line #'(1.5 . 0)
                          \musicglyph #"accidentals.natural"
                        }
                      #}))
    #my-music
    \revert Staff.KeySignature.stencil
    #}
  )

keysigBmiBmiBass = 
  #(define-music-function (P L my-music)
                          (ly:music?)
    #{
      \set Staff.keyAlterations = #`(((-1 . 6) . ,NATURAL)
                                     (( 0 . 6) . ,NATURAL))
      \set Staff.printKeyCancellation = ##f 
      \temporary \override Staff.KeySignature.stencil =
      #(lambda (grob) (grob-interpret-markup grob
                      #{
                        \markup
                        {
                        \combine 
                        \translate #'(0 . -1)  
                        \musicglyph #"accidentals.natural"
                        \translate #'(0 . 2.5)
                        \musicglyph #"accidentals.natural"
                        }
                      #}))
    #my-music
    \revert Staff.KeySignature.stencil
    #}
  )


% Test harness begins...

% N.B. Important to test:
% 1. Change of keysig;
% 2. Continuation of keysig onto new line;
% 3. Cancellation of keysig, and any residual effects.

%{ % begin block comment...

music = {
  b,2 bes b' bes
  \break
  b,2 bes b' bes
}

\relative c'' {
  \keysigBfaBmiTreble \music
  
  \keysigBfaBfaTreble \music
  
  \keysigBfaBmiTreble \music
  
  \keysigBmiBmiTreble \music
  
  \key f \major \music
  
  \clef "bass"
  
  \keysigBfaBmiBass { b,1 \music }
  
  \keysigBfaBfaBass \music
  
  \keysigBfaBmiBass \music
  
  \keysigBmiBmiBass \music
  
  \key f \major \music
}  

\layout {
  ragged-right = ##t
}
%}
% ... Test harness ends