Функция смены тональности песен с аккордамы

                        
function alterate($chords_string, $half_tones_alt) 

{ 

$data_half_tones = array( 

0 => 'C', 

2 => 'D', 

4 => 'E', 

5 => 'F', 

7 => 'G', 

9 => 'A', 

10 => 'B', 

11 => 'H', 

); 



$wrong_alts = array( 

'A#' => 'B', 

'B#' => 'H', 

'H#' => 'C', 

'E#' => 'F', 

); 



$data_chords = array_flip($data_half_tones); 



$strlen = strlen($chords_string); 

$return = ''; 



for($i = 0; $i < $strlen; $i++) 

{ 

if(in_array($chords_string[$i], $data_half_tones)) 

{ 

$new_tone = $data_chords[$chords_string[$i]] + $half_tones_alt; 

$new_tone = ($new_tone > 11 ? $new_tone % 12 : $new_tone); 

$return .= (array_key_exists($new_tone, $data_half_tones) 

? $data_half_tones[$new_tone] 

: (array_key_exists($data_half_tones[$new_tone - 1].'#', $wrong_alts) 

? $wrong_alts[$data_half_tones[$new_tone - 1].'#'] 

: $data_half_tones[$new_tone - 1].'#' 

) 



); 



} 

else 

{ 

$return .= $chords_string[$i]; 

} 



} 







return $return; 

} 



echo alterate('Em H7 Em H7', +2); 



//F#m C#7 F#m C#7