Gendoria\CruftFlake\Generator\Generator

Complexity

Total Complexity

19

Size/Duplication

Total Lines	206
Duplicated Lines	0 %

Coupling/Cohesion

Components	1
Dependencies	3

Test Coverage

Coverage

100%

Importance

Changes	5
Bugs	1	Features	1

9 Methods

Rating	Name	Duplication	Size	Complexity
A	__construct()	0	10	4
A	generate()	0	15	3
A	is32Bit()	0	4	1
A	generateWithDifferentTime()	0	20	4
A	generateWithSameTime()	0	9	2
A	status()	0	5	1
A	mintId32()	0	15	1
A	mintId64()	0	7	1
A	hexdec()	0	10	2

<?php

/**
 * Like the Twitter one.
 * 
 * 64 bits:
 * 
 * time - 41 bits (millisecond precision w/ a custom epoch gives us 69 years)
 * configured machine id - 10 bits - gives us up to 1024 machines
 * sequence number - 12 bits - rolls over every 4096 per machine (with protection to avoid rollover in the same ms)
 * 
 * 32 bits + 9 = 41 bits of time
 * 2199023255552 < milliseconds = 2199023255 seconds
 *                                2147483647 < max 31 bit int (signed)
 *
 * @author @davegardnerisme
 */

namespace Gendoria\CruftFlake\Generator;

use Gendoria\CruftFlake\Config\ConfigInterface;
use Gendoria\CruftFlake\Timer\TimerInterface;
use InvalidArgumentException;
use OverflowException;
use UnexpectedValueException;

class Generator
{

    /**
     * Max timestamp.
     */
    const MAX_ADJUSTED_TIMESTAMP = 2199023255551;

    /**
     * Hexdec lookup.
     * 
     * @staticvar array
     */
    private static $hexdec = array(
        '0' => 0,
        '1' => 1,
        '2' => 2,
        '3' => 3,
        '4' => 4,
        '5' => 5,
        '6' => 6,
        '7' => 7,
        '8' => 8,
        '9' => 9,
        'a' => 10,
        'b' => 11,
        'c' => 12,
        'd' => 13,
        'e' => 14,
        'f' => 15,
    );

    /**
     * Timer.
     * 
     * @var TimerInterface
     */
    private $timer;

    /**
     * Configured machine ID - 10 bits (dec 0 -> 1023).
     *
     * @var int
     */
    private $machine;

    /**
     * Epoch - in UTC millisecond timestamp.
     *
     * @var int
     */
    private $epoch = 1325376000000;

    /**
     * Sequence number - 12 bits, we auto-increment for same-millisecond collisions.
     *
     * @var int
     */
    private $sequence = 1;

    /**
     * The most recent millisecond time window encountered.
     *
     * @var int
     */
    private $lastTime = null;

    /**
     * Constructor.
     * 
     * @param @inject ConfigInterface $config
     * @param @inject TimerInterface  $timer
     */
    public function __construct(ConfigInterface $config, TimerInterface $timer)
    {
        $this->machine = $config->getMachine();
        if (!is_int($this->machine) || $this->machine < 0 || $this->machine > 1023) {
            throw new InvalidArgumentException(
            'Machine identifier invalid -- must be 10 bit integer (0 to 1023)'
            );
        }
        $this->timer = $timer;
    }

    /**
     * Generate ID.
     *
     * @return string A 64 bit integer as a string of numbers (so we can deal
     *                with this on 32 bit platforms) 
     */
    public function generate()
    {
        $t = (int) floor($this->timer->getUnixTimestamp() - $this->epoch);
        if ($t !== $this->lastTime) {
            $this->generateWithDifferentTime($t);
        } else {
            $this->generateWithSameTime();
        }

        if ($this->is32Bit()) {
            return $this->mintId32($t, $this->machine, $this->sequence);
        } else {
            return $this->mintId64($t, $this->machine, $this->sequence);
        }
    }
    
    /**
     * Return true, if we are on 32 bit platform.
     * 
     * @return boolean
     */
    protected function is32Bit()
    {
        return (PHP_INT_SIZE === 4);
    }

    /**
     * Generate new ID with different time.
     * 
     * @param integer $t
     * @throws UnexpectedValueException
     * @throws OverflowException
     */
    private function generateWithDifferentTime($t)
    {
        if ($t < $this->lastTime) {
            throw new UnexpectedValueException(
            'Time moved backwards. We cannot generate IDs for '
            . ($this->lastTime - $t) . ' milliseconds'
            );
        } elseif ($t < 0) {
            throw new UnexpectedValueException(
            'Time is currently set before our epoch - unable '
            . 'to generate IDs for ' . (-$t) . ' milliseconds'
            );
        } elseif ($t > self::MAX_ADJUSTED_TIMESTAMP) {
            throw new OverflowException(
            'Timestamp overflow (past end of lifespan) - unable to generate any more IDs'
            );
        }
        $this->sequence = 0;
        $this->lastTime = $t;
    }

    /**
     * Generate new ID with same time.
     * 
     * @throws OverflowException
     */
    private function generateWithSameTime()
    {
        ++$this->sequence;
        if ($this->sequence > 4095) {
            throw new OverflowException(
            'Sequence overflow (too many IDs generated) - unable to generate IDs for 1 milliseconds'
            );
        }
    }

    /**
     * Get stats.
     *
     * @return GeneratorStatus
     */
    public function status()
    {
        return new GeneratorStatus($this->machine, $this->lastTime,
            $this->sequence, (PHP_INT_SIZE === 4));
    }

    private function mintId32($timestamp, $machine, $sequence)
    {
        $hi = (int) ($timestamp / pow(2, 10));
        $lo = (int) ($timestamp * pow(2, 22));

        // stick in the machine + sequence to the low bit
        $lo = $lo | ($machine << 12) | $sequence;

        // reconstruct into a string of numbers
        $hex = pack('N2', $hi, $lo);
        $unpacked = unpack('H*', $hex);
        $value = $this->hexdec($unpacked[1]);

        return (string) $value;
    }

    private function mintId64($timestamp, $machine, $sequence)
    {
        $timestamp = (int) $timestamp;
        $value = ($timestamp << 22) | ($machine << 12) | $sequence;

        return (string) $value;
    }

    private function hexdec($hex)
    {
        $dec = 0;
        for ($i = strlen($hex) - 1, $e = 1; $i >= 0; $i--, $e = bcmul($e, 16)) {
            $factor = self::$hexdec[$hex[$i]];
            $dec = bcadd($dec, bcmul($factor, $e));
        }

        return $dec;
    }

}