<?php

declare(strict_types=1);

namespace App\Engine\Cfnpp\Expression;

/**
 * Token representing a function.
 *
 * @author Adam Pippin <hello@adampippin.ca>
 */
class TokenFunction extends Token
{
	/**
	 * List of valid functions this can parse.
	 * @var string[]
	 */
	public const FUNCTIONS = [
		'concat*',
		'concat'
	];

	/**
	 * Function this token represents.
	 * @var string
	 */
	protected $function;

	/**
	 * Create a new function token.
	 *
	 * @param string $function
	 */
	public function __construct($function)
	{
		$this->function = $function;
	}

	/**
	 * Get the function this token represents.
	 *
	 * @return string
	 */
	public function getFunction(): string
	{
		return $this->function;
	}

	/**
	 * Determine whether a function token can be parsed from a stream.
	 *
	 * @param  string $stream
	 * @return bool
	 */
	public static function isToken(string $stream): bool
	{
		foreach (static::FUNCTIONS as $function)
		{
			if (strlen($stream) > strlen($function) &&
				substr($stream, 0, strlen($function)) == $function)
			{
				return true;
			}
		}
		return false;
	}

	/**
	 * Parse a function token from a stream.
	 *
	 * Returns token, and modifies stream to remove all consumed characters
	 *
	 * @param  string $stream
	 * @return Token
	 */
	public static function getToken(string &$stream): Token
	{
		foreach (static::FUNCTIONS as $function)
		{
			if (strlen($stream) > strlen($function) &&
				substr($stream, 0, strlen($function)) == $function)
			{
				$function = substr($stream, 0, strlen($function));
				$stream = substr($stream, strlen($function));
				return new TokenFunction($function);
			}
		}
		throw new \Exception('Could not parse function token!');
	}
}