<?php

/**
 * This file is part of the ramsey/uuid library
 *
 * For the full copyright and license information, please view the LICENSE
 * file that was distributed with this source code.
 *
 * @copyright Copyright (c) Ben Ramsey <ben@benramsey.com>
 * @license http://opensource.org/licenses/MIT MIT
 */

declare(strict_types=1);

namespace Ramsey\Uuid\Generator;

use Ramsey\Uuid\Converter\NumberConverterInterface;
use Ramsey\Uuid\Exception\InvalidArgumentException;

use function bin2hex;
use function explode;
use function hex2bin;
use function microtime;
use function str_pad;
use function substr;

use const STR_PAD_LEFT;

/**
 * CombGenerator generates COMBs (combined UUID/timestamp)
 *
 * The CombGenerator, when used with the StringCodec (and, by proxy, the
 * TimestampLastCombCodec) or the TimestampFirstCombCodec, combines the current
 * timestamp with a UUID (hence the name "COMB"). The timestamp either appears
 * as the first or last 48 bits of the COMB, depending on the codec used.
 *
 * By default, COMBs will have the timestamp set as the last 48 bits of the
 * identifier.
 *
 * ``` php
 * $factory = new UuidFactory();
 *
 * $factory->setRandomGenerator(new CombGenerator(
 *     $factory->getRandomGenerator(),
 *     $factory->getNumberConverter()
 * ));
 *
 * $comb = $factory->uuid4();
 * ```
 *
 * To generate a COMB with the timestamp as the first 48 bits, set the
 * TimestampFirstCombCodec as the codec.
 *
 * ``` php
 * $factory->setCodec(new TimestampFirstCombCodec($factory->getUuidBuilder()));
 * ```
 *
 * @link https://www.informit.com/articles/printerfriendly/25862 The Cost of GUIDs as Primary Keys
 */
class CombGenerator implements RandomGeneratorInterface
{
    public const TIMESTAMP_BYTES = 6;

    /**
     * @var RandomGeneratorInterface
     */
    private $randomGenerator;

    /**
     * @var NumberConverterInterface
     */
    private $converter;

    public function __construct(
        RandomGeneratorInterface $generator,
        NumberConverterInterface $numberConverter
    ) {
        $this->converter = $numberConverter;
        $this->randomGenerator = $generator;
    }

    /**
     * @throws InvalidArgumentException if $length is not a positive integer
     *     greater than or equal to CombGenerator::TIMESTAMP_BYTES
     *
     * @inheritDoc
     */
    public function generate(int $length): string
    {
        if ($length < self::TIMESTAMP_BYTES || $length < 0) {
            throw new InvalidArgumentException(
                'Length must be a positive integer greater than or equal to ' . self::TIMESTAMP_BYTES
            );
        }

        $hash = '';
        if (self::TIMESTAMP_BYTES > 0 && $length > self::TIMESTAMP_BYTES) {
            $hash = $this->randomGenerator->generate($length - self::TIMESTAMP_BYTES);
        }

        $lsbTime = str_pad(
            $this->converter->toHex($this->timestamp()),
            self::TIMESTAMP_BYTES * 2,
            '0',
            STR_PAD_LEFT
        );

        return (string) hex2bin(
            str_pad(
                bin2hex((string) $hash),
                $length - self::TIMESTAMP_BYTES,
                '0'
            )
            . $lsbTime
        );
    }

    /**
     * Returns current timestamp a string integer, precise to 0.00001 seconds
     */
    private function timestamp(): string
    {
        $time = explode(' ', microtime(false));

        return $time[1] . substr($time[0], 2, 5);
    }
}
