Color palette generator

colors.php

/**
 * Class Colors.
 * Pallete Generator Helper.
 */
class Colors implements \Iterator, \ArrayAccess
{

    const COL_MIN_AVG = 64;
    const COL_MAX_AVG = 192;
    const COL_STEP    = 16;
    const SEED        = 'vvtdljnufvnluvievkdffectltuhvllrccrrtelfvvec';


    /**
     * Sequence pointer.
     *
     * @var int
     */
    protected $sequence_pointer = 0;


    /**
     * Generate a color sequence in HEX format
     * @param $num
     * @return string   color as hexadecimal string
     */
    public static function getHexColorSequence($num)
    {

        // Append color seed
        $num .= static::SEED;

        $range = static::COL_MAX_AVG - static::COL_MIN_AVG;
        $factor = $range / 256;
        $offset = static::COL_MIN_AVG;

        $base_hash = substr(md5($num), 0, 6);
        $b_R = hexdec(substr($base_hash,0,2));
        $b_G = hexdec(substr($base_hash,2,2));
        $b_B = hexdec(substr($base_hash,4,2));

        $f_R = floor((floor($b_R * $factor) + $offset) / static::COL_STEP) * static::COL_STEP;
        $f_G = floor((floor($b_G * $factor) + $offset) / static::COL_STEP) * static::COL_STEP;
        $f_B = floor((floor($b_B * $factor) + $offset) / static::COL_STEP) * static::COL_STEP;

        return sprintf('%02x%02x%02x', $f_R, $f_G, $f_B);
    }


    /**
     * Return current value
     *
     * @return int
     */
    public function current()
    {
        return static::getHexColorSequence($this->sequence_pointer);
    }


    /**
     * Get next value
     */
    public function next()
    {
        ++$this->sequence_pointer;
    }


    /**
     * Rewind
     */
    public function rewind()
    {
        $this->sequence_pointer = 0;
    }


    /**
     * Get current key.
     *
     * @return int
     */
    public function key()
    {
        return $this->sequence_pointer;
    }


    /**
     * Check if current index is valid.
     *
     * @return bool
     */
    public function valid()
    {
        return true;
    }


    /**
     * Check if offset exists.
     *
     * @param mixed $offset
     * @return bool
     */
    public function offsetExists($offset)
    {
        if (is_int($offset))
            return true;
    }


    /**
     * Return value by index.
     *
     * @param mixed $index
     * @return string
     */
    public function offsetGet($index)
    {
        return static::getHexColorSequence($index);
    }


    /**
     * Set a value, however Colors is read-only.
     *
     * @param mixed $offset
     * @param mixed $value
     */
    public function offsetSet($offset, $value)
    {
        // Nothing to do, Colors is read-only
    }


    /**
     * Remove index, however Colors is read-only.
     *
     * @param mixed $index
     */
    public function offsetUnset($index)
    {
        // Nothing to do, Colors is read-only
    }

}