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<?

/**

Calculates the percentage change between two numbers.
Useful for showing how much traffic has changed from one time period to the next.

*/

$percentChange = function ($cur, $prev) {
  if ($cur == 0) {
    if ($prev == 0) {
      return array('diff' => 0, 'trend' => '');
    }
    return array('diff' => -($prev * 100), 'trend' => 'down_arrow');
  }
  if ($prev == 0) {
    return array('diff' => $cur * 100, 'trend' => 'up_arrow');
  }
  $difference = ($cur - $prev) / $prev * 100;
  $trend = '';
  if ($cur > $prev) {
    $trend = 'up_arrow';
  } else if ($cur < $prev) {
    $trend = 'down_arrow';
  }
  return array('diff' => round($difference, 0), 'trend' => $trend);
};

### TESTS ###

# Decreasing
print_r($percentChange(2, 7)); print "\n";

# Increasing
print_r($percentChange(7, 3)); print "\n";

# Increasing
print_r($percentChange(7, 0)); print "\n";

# Decreasing
print_r($percentChange(0, 2)); print "\n";

# No change
print_r($percentChange(0, 0)); print "\n";

?>