grammar Clef

  rule statement
    assignment / expression
  end
  
  rule expression
    additive
  end

  rule assignment
    channel 
    space '=' space
    expression {
      def evaluate(env)
        env.play(channel.evaluate(env).to_i, expression.evaluate(env))
      end
    }
  end

  rule additive
    operand1:multitive
    space operator:additive_operator space
    operand2:additive {
      def evaluate(env)
        operator.apply(operand1.evaluate(env), operand2.evaluate(env))
      end
    }
    /
    multitive
  end

  rule additive_operator
    '+' {
      def apply(a, b)
        a + b
      end
    }
    / 
    '-' {
      def apply(a, b)
        a - b
      end
    }
  end

  rule multitive
    operand1:primary
    space operator:multitive_operator space
    operand2:multitive {
      def evaluate(env)
        operator.apply(operand1.evaluate(env), operand2.evaluate(env))
      end
    }
    /
    primary
  end

  rule multitive_operator
    '*' {
      def apply(a, b)
        a * b
      end
    }
    /
    '/' {
      def apply(a, b)
        a / b
      end
    }
    /
    '&' {
      def apply(a, b)
        a & b
      end
    }
  end

  rule primary
    sequence 
    / 
    integer
    /
    channel
    /
    '(' space expression space ')' { 
      def evaluate(env)
        expression.evaluate(env)
      end
    }
  end

  rule sequence
    '[' playables ']' {
      def evaluate(env)
        Clef::Sequence.new(playables.evaluate(env))
      end
    }
  end

  rule key
    [A-Ga-g] { 
      def evaluate(env)
        text_value
      end
    }
  end

  rule accent
    ('-' / '#') {
      def evaluate(env)
        text_value
      end
    }
  end

  rule integer
    '-'? [0-9]+ {
      def evaluate(env)
        text_value.to_i
      end
    }
  end

  rule octave
    [0-9] {
      def evaluate(env)
        text_value.to_i
      end
    }
  end

  rule note
    key accent octave {
      def evaluate(env)
        Clef::Note.new(
          key.evaluate(env), 
          accent.evaluate(env), 
          octave.evaluate(env))
      end
    }
    /
    rest
  end

  rule notes 
    note space notes {
      def evaluate(env)
        [ note.evaluate(env), notes.evaluate(env) ].flatten
      end
    }
    /
    note
  end

  rule rest
    '_'+ {
      def evaluate(env)
        Clef::Rest.new
      end
    }
  end

  rule harmony 
    '(' space notes space ')' {
      def evaluate(env)
        Harmony.new(notes.evaluate(env))
      end
    }
  end

  rule playable
    note / harmony
  end

  rule playables
    playable space playables {
      def evaluate(env)
        [ playable.evaluate(env), playables.evaluate(env) ].flatten
      end
    }
    /
    playable
  end

  rule channel_number
    '0' / '1' / '2' / '3' / '4' / '5' / '6' / '7' / '8' / '9' / '10' / '11' / '12' / '13' / '14' / '15'
  end

  rule channel
    '@' channel_number {
      def evaluate(env)
        env.channels[channel_number.text_value.to_i]
      end
    }
  end

  rule space
    ' '*
  end

end