/**
* Get the conversion factor between two Units of Weight
*
* e.g. from LB to OZ = 16
*
* @author Tom Haskins-Vaughan <*****@*****.**>
* @since 0.3.0
*
* @param Uom $from
* @param Uom $to
*
* @throws ConversionNotSetException Thown when a conversion is tried
* that has not been set in the conversions.json file
* @throws BadConversionException Thrown when a conversion is not set
* properly, e.g. [1] should be [1, 16]
* @return Fraction
*/
public static function getConversionFactor(Uom $from, Uom $to)
{
// Check to see if we need to do a conversion
if ($from->isSameValueAs($to)) {
return new Fraction(1);
}
if (!isset(static::$conversions)) {
static::$conversions = json_decode(utf8_encode(file_get_contents(__DIR__ . '/conversions.json')), true);
}
// First lets see if we have a conversion for the from to to
if (isset(static::$conversions[$from->getName()][$to->getName()])) {
$numeratorDenominatorPair = static::$conversions[$from->getName()][$to->getName()];
// I guess we didn't find one, try the inverse
} elseif (isset(static::$conversions[$to->getName()][$from->getName()])) {
// We found the inverse, set the conversion values appropriately
$numeratorDenominatorPair = array_reverse(static::$conversions[$to->getName()][$from->getName()]);
} else {
// no conversion found. throw an exception
throw new ConversionNotSetException($from->getName(), $to->getName());
}
// Is the conversion set up correctly
if (count($numeratorDenominatorPair) == 2) {
return new Fraction($numeratorDenominatorPair[0], $numeratorDenominatorPair[1]);
} else {
// Guess it wasn't
throw new BadConversionException();
}
}
