000-usage.php

<?php

//
// Create a monthly task that happens every five months
// and needs to be completed within 5 days.
//

// uses the 'by' "constructor" for Completed
 
$taskRecurrence = TaskRecurrence::forRecurrence(Recurrence::MONTHLY())
    ->withInterval(Interval::fromNumber(5))
    ->mustBe(Completed::by(Designator::DAY(), 5));

 
//
// Create a monthly task that happens every month that
// needs to be completed on each of the 1st, 3rd, and
// 5th days of the month.
//

// uses the 'onDays' "constructor" for Completed
 
$taskRecurrence = TaskRecurrence::forRecurrence(Recurrence::MONTHLY())
    ->mustBe(Completed::onDays([1, 3, 5]));

Completed.php

<?php

class Completed implements JsonSerializable, JsonDeserializable
{
    /**
     * @var string
     */
    private $type;

    /**
     * @var Designator
     */
    private $byDesignator;

    /**
     * @var int
     */
    private $byNumber;

    /**
     * @var int[]
     */
    private $onDays = [];

    private function __construct($type)
    {
        $this->type = $type;
    }

    /**
     * @param Designator $designator
     * @param $number
     * @return static
     */
    public static function by(Designator $designator, $number)
    {
        $instance = new static('by');

        $instance->byDesignator = $designator;
        $instance->byNumber = $number;

        return $instance;
    }

    /**
     * @param int[] $days
     * @return static
     */
    public static function onDays(array $days)
    {
        $instance = new static('on');

        $instance->onDays = $days;

        return $instance;
    }

    /**
     * @return static
     */
    public static function anytime()
    {
        return new static('anytime');
    }

    /**
     * @return bool
     */
    public function isBy()
    {
        return 'by' === $this->type;
    }

    /**
     * @return bool
     */
    public function isOnDays()
    {
        return 'on' === $this->type;
    }

    /**
     * @return bool
     */
    public function isAnytime()
    {
        return 'anytime' === $this->type;
    }

    /**
     * @return Designator
     */
    public function getByDesignator()
    {
        return $this->byDesignator;
    }

    /**
     * @return int
     */
    public function getByNumber()
    {
        return $this->byNumber;
    }

    /**
     * @return \int[]
     */
    public function getOnDays()
    {
        return $this->onDays;
    }

    /**
     * @return array|mixed
     */
    public function jsonSerialize()
    {
        return [
            'type' => $this->type,
            'byNumber' => $this->byNumber,
            'byDesignator' => $this->byDesignator,
            'onDays' => $this->onDays,
        ];
    }

    /**
     * @param $data
     * @return static
     */
    public static function jsonDeserialize($data)
    {
        $instance = new static($data['type']);

        $instance->byNumber = $data['byNumber'];
        $instance->byDesignator = Designator::jsonDeserialize($data['byDesignator']);
        $instance->onDays = $data['onDays'];

        return $instance;
    }
}

Designator.php

<?php

class Designator implements JsonSerializable, JsonDeserializable
{
    private $name;

    private function __construct($name)
    {
        $this->name = $name;
    }

    public function __toString()
    {
        return (string) $this->name;
    }

    public static function fromString($string)
    {
        return new static(strtoupper($string));
    }

    public static function DAY()
    {
        return static::fromString('DAY');
    }

    public static function WEEK()
    {
        return static::fromString('WEEK');
    }

    public static function YEAR()
    {
        return static::fromString('YEAR');
    }

    public function equals(Designator $other)
    {
        return $this->name === $other->name;
    }

    public function jsonSerialize()
    {
        return $this->name;
    }

    public static function jsonDeserialize($data)
    {
        return new static($data);
    }
}