Stripe Subscription Cancellation and Prorated Refund

refund.php

<?php

class StripeSubscriptionHandler {

	/**
	 * Cancel a Stripe subscription, optionally prorating and refunding the unused amount
	 *
	 * @param string $id            Stripe Subscription ID
	 * @param bool   $at_period_end Type of cancellation
	 *                              If set to true, will cancel the subscription at its end
	 *                              Otherwise, will cancel the subscription immediately
	 * @param bool   $prorate       Issue a prorated refund
	 *                              If set to true, will prorate the unused part of the subscription and issue a refund
	 *
	 * @return \Stripe\Subscription
	 */
	public function cancel($id, $at_period_end = true, $prorate = false) {

		$subscription = \Stripe\Subscription::retrieve($id);
		/* @var $subscription \Stripe\Subscription */

		if (!$at_period_end && $prorate) {

			$time = new \DateTime('now', new \DateTimeZone('UTC'));

			$refund = $this->prorate($subscription, $time);

			if ($refund) {
				$invoices = \Stripe\Invoice::all([
					'subscription' => $subscription->id,
				]);

				if ($invoices->count()) {
					$invoice = $invoices->data[0];

					\Stripe\Refund::create([
						'charge' => $invoice->charge,
						'amount' => $refund,
					]);
				}
			}
		}

		return $subscription->cancel([
			'at_period_end' => $at_period_end,
		]);
	}

	/**
	 * Calculate refund amount on an unsused part of the subscription
	 *
	 * @param \Stripe\Subscription $subscription Stripe Subscription
	 * @param DateTime             $time         Time of the cancellation
	 *
	 * @return int
	 */
	public function prorate(\Stripe\Subscription $subscription, DateTime $time) {
		$period_start = $subscription->current_period_start;
		$period_end = $subscription->current_period_end;
		$amount = $subscription->plan->amount;

		$period_length = $period_end - $period_start;

		$elapsed_since_start = $time->getTimestamp() - $period_start;

		$refund = $amount - floor(($elapsed_since_start / $period_length) * $amount);

		return $refund > 0 ? (int) $refund : 0;
	}
}

class StripeSubscriptionTest extends \PHPUnit\Framework\TestCase {

	/**
	 * @var StripeSubscriptionHandler
	 */
	protected $handler;

	public function setUp() {
		$this->handler = new StripeSubscriptionHandler();
	}

	/**
	 * @dataProvider prorationProvider
	 */
	public function testProrate($start, $end, $cancel, $amount, $expected) {

		$subscription = new \Stripe\Subscription();

		$start_at = new DateTime($start, new DateTimeZone('UTC'));
		$end_at = new DateTime($end, new DateTimeZone('UTC'));
		$cancel_at = new DateTime($cancel, new DateTimeZone('UTC'));

		$subscription->current_period_start = $start_at->getTimestamp();
		$subscription->current_period_end = $end_at->getTimestamp();

		$subscription->plan = new \Stripe\Plan();
		$subscription->plan->amount = $amount;

		$actual = $this->handler->prorate($subscription, $cancel_at);

		$this->assertEquals($expected, $actual);
	}

	public function prorationProvider() {
		return [
			[
				'Jan 1, 2018 0:00:00',
				'Jan 31, 2018 23:59:59',
				'Jan 5, 2018 12:00:00',
				1000,
				855,
			],
			[
				'Jan 1, 2018 0:00:00',
				'Dec 31, 2018 23:59:59',
				'Jun 30, 2018 23:59:59',
				1000,
				505,
			],
			[
				'Jan 5, 2018 0:00:00',
				'Jan 5, 2018 1:00:00',
				'Jan 5, 2018 0:30:00',
				1000,
				500,
			],
		];
	}
}