<?php

declare(strict_types=1);

namespace App\Engine\Cfnpp\Expression;

/**
 * Parse a string into a series of expression tokens.
 *
 * @author Adam Pippin <hello@adampippin.ca>
 */
class Parser
{
	/**
	 * List of class names of tokens this parser will parse.
	 *
	 * @var string[]
	 */
	public const TOKEN_TYPES = [
		TokenFunction::class,
		TokenNumericLiteral::class,
		TokenOperator::class,
		TokenStringLiteral::class,
		TokenVariable::class
	];

	/**
	 * Parse a string into an expression.
	 *
	 * @param  string     $value
	 * @return Expression
	 */
	public function parse(string $value): Expression
	{
		$original_value = $value;
		$value .= ' ';
		$tokens = [];
		while (strlen($value) > 0)
		{
			foreach (static::TOKEN_TYPES as $token_class)
			{
				if ($token_class::isToken($value))
				{
					$tokens[] = $token_class::getToken($value);

					if (substr($value, 0, 1) != ' ')
					{
						throw new \Exception('Incompletely consumed token at offset '.(strlen($original_value) - strlen($value)).' in expression '.$original_value);
					}

					$value = substr($value, 1);
					continue 2;
				}
			}

			throw new \Exception('Unparseable value at offset '.(strlen($original_value) - strlen($value)).' in expression '.$original_value);
		}

		return new Expression($tokens);
	}
}