<?php

namespace TablePress\PhpOffice\PhpSpreadsheet\Reader\Xls;

class RC4
{
	/** @var int[] */
	protected array $s = []; // Context

	protected int $i = 0;

	protected int $j = 0;

	/**
	 * RC4 stream decryption/encryption constrcutor.
	 *
	 * @param string $key Encryption key/passphrase
	 */
	public function __construct(string $key)
	{
		$len = strlen($key);

		for ($this->i = 0; $this->i < 256; ++$this->i) {
			$this->s[$this->i] = $this->i;
		}

		$this->j = 0;
		for ($this->i = 0; $this->i < 256; ++$this->i) {
			$this->j = ($this->j + $this->s[$this->i] + ord($key[$this->i % $len])) % 256;
			$t = $this->s[$this->i];
			$this->s[$this->i] = $this->s[$this->j];
			$this->s[$this->j] = $t;
		}
		$this->i = $this->j = 0;
	}

	/**
	 * Symmetric decryption/encryption function.
	 *
	 * @param string $data Data to encrypt/decrypt
	 */
	public function RC4(string $data): string
	{
		$len = strlen($data);
		for ($c = 0; $c < $len; ++$c) {
			$this->i = ($this->i + 1) % 256;
			$this->j = ($this->j + $this->s[$this->i]) % 256;
			$t = $this->s[$this->i];
			$this->s[$this->i] = $this->s[$this->j];
			$this->s[$this->j] = $t;

			$t = ($this->s[$this->i] + $this->s[$this->j]) % 256;

			$data[$c] = chr(ord($data[$c]) ^ $this->s[$t]);
		}

		return $data;
	}
}
