/**
* Rearranges tokens according to RPN (Reverse Polish Notation) or
* also known as Postfix Notation.
*
* @param array $tokens
* @return \SplQueue
* @throws \InvalidArgumentException
*/
public function getReversePolishNotation(array $tokens)
{
$queue = new \SplQueue();
$stack = new \SplStack();
$tokensCount = count($tokens);
for ($i = 0; $i < $tokensCount; $i++) {
if (is_numeric($tokens[$i])) {
// (string + 0) converts to int or float
$queue->enqueue($tokens[$i] + 0);
} else {
if (array_key_exists($tokens[$i], $this->_functions)) {
$stack->push($tokens[$i]);
} else {
if ($tokens[$i] === self::FUNC_ARG_SEPARATOR) {
// checking whether stack contains left parenthesis (dirty hack)
if (substr_count($stack->serialize(), '(') === 0) {
throw new \InvalidArgumentException('Parenthesis are misplaced');
}
while ($stack->top() != '(') {
$queue->enqueue($stack->pop());
}
} else {
if (in_array($tokens[$i], $this->_operators)) {
while ($stack->count() > 0 && in_array($stack->top(), $this->_operators) && ($this->isOperatorLeftAssociative($tokens[$i]) && $this->getOperatorPrecedence($tokens[$i]) === $this->getOperatorPrecedence($stack->top()) || $this->getOperatorPrecedence($tokens[$i]) < $this->getOperatorPrecedence($stack->top()))) {
$queue->enqueue($stack->pop());
}
$stack->push($tokens[$i]);
} else {
if ($tokens[$i] === '(') {
$stack->push('(');
} else {
if ($tokens[$i] === ')') {
// checking whether stack contains left parenthesis (dirty hack)
if (substr_count($stack->serialize(), '(') === 0) {
throw new \InvalidArgumentException('Parenthesis are misplaced');
}
while ($stack->top() != '(') {
$queue->enqueue($stack->pop());
}
$stack->pop();
if ($stack->count() > 0 && array_key_exists($stack->top(), $this->_functions)) {
$queue->enqueue($stack->pop());
}
}
}
}
}
}
}
}
while ($stack->count() > 0) {
$queue->enqueue($stack->pop());
}
return $queue;
}