cfnpp/app/Engine/Cfnpp/Expression/Expression.php

<?php

declare(strict_types=1);

namespace App\Engine\Cfnpp\Expression;

class Expression
{
	protected $tokens;

	protected $stack;

	protected $variables;

	public function __construct(array $tokens)
	{
		$this->tokens = $tokens;
	}

	public function evaluate(array $variables = [])
	{
		$this->variables = $variables;
		$this->stack = [];
		$tokens = $this->tokens;

		while (sizeof($tokens))
		{
			$token = array_shift($tokens);

			if ($token instanceof TokenNumericLiteral)
			{
				$this->evaluateTokenNumericLiteral($token);
			}
			elseif ($token instanceof TokenStringLiteral)
			{
				$this->evaluateTokenStringLiteral($token);
			}
			elseif ($token instanceof TokenOperator)
			{
				$this->evaluateTokenOperator($token);
			}
			elseif ($token instanceof TokenVariable)
			{
				$this->evaluateTokenVariable($token);
			}
			else
			{
				throw new \Exception('Unhandled expression token type: '.basename(get_class($token)));
			}
		}

		if (sizeof($this->stack) != 1)
		{
			throw new \Exception('Expression did not evaluate down to a single value');
		}

		return $this->stack[0];
	}

	protected function evaluateTokenNumericLiteral(TokenNumericLiteral $token)
	{
		$this->push($token->getValue());
	}

	protected function evaluateTokenStringLiteral(TokenStringLiteral $token)
	{
		$this->push($token->getValue());
	}

	protected function evaluateTokenOperator(TokenOperator $token)
	{
		switch ($token->getOperator())
		{
			case 'eq':
				$this->push($this->pop() == $this->pop());
				break;
			case 'neq':
				$this->push($this->pop() != $this->pop());
				break;
			case 'gt':
				$this->push($this->pop(1) > $this->pop());
				break;
			case 'gte':
				$this->push($this->pop(1) >= $this->pop());
				break;
			case 'lt':
				$this->push($this->pop(1) < $this->pop());
				break;
			case 'lte':
				$this->push($this->pop(1) <= $this->pop());
				break;
			case 'and':
				$var1 = $this->pop();
				$var2 = $this->pop();
				$this->push($var1 && $var2);
				break;
			case 'or':
				$var1 = $this->pop();
				$var2 = $this->pop();
				$this->push($var1 || $var2);
				break;
		}
	}

	protected function evaluateTokenVariable(TokenVariable $token)
	{
		$name = $token->getName();
		if (!isset($this->variables[$name]))
		{
			throw new \Exception('Undefined variable: '.$name);
		}
		$this->push($this->variables[$name]);
	}

	protected function pop(int $offset = 0)
	{
		return array_splice($this->stack, -1 * ($offset + 1), 1)[0];
	}

	protected function push($value)
	{
		array_push($this->stack, $value);
	}
}