Estimate billing periods between two timestamps (for WCS Resource) + unit tests

estimate-billing-periods.php

<?php

	/**
	 * Estimate the billing periods between two timestamps
	 *
	 * @since 1.0
	 * @param int $from_timestamp
	 * @param int $to_timestamp
	 * @param string $billing_period
	 * @param string $billing_interval
	 * @return array
	 */
	public function estimate_resource_billing_periods_between( $from_timestamp, $to_timestamp, $billing_period, $billing_interval ) {
		$billing_periods_between = array();
		$counter                 = 0;

		while ( $from_timestamp < $to_timestamp && $counter < 100 ) {
			$current_billing_period = array( 'from_timestamp' => $from_timestamp );
			$next_timestamp         = wcs_add_time( $billing_interval, $billing_period, $from_timestamp ); // use the same function used to calculate subscription billing periods to work out the exact billing

			if ( $to_timestamp < $next_timestamp ) {
				$current_billing_period['to_timestamp'] = $to_timestamp;
				$current_billing_period['period_fraction'] = round( ( $from_timestamp - $to_timestamp ) / ( $from_timestamp - $next_timestamp ), 2);
			} else {
				$current_billing_period['to_timestamp'] = ( $to_timestamp - $next_timestamp > DAY_IN_SECONDS ) ? $next_timestamp : $to_timestamp;
				$current_billing_period['period_fraction'] = 1;
			}

			$from_timestamp            = $next_timestamp;
			$billing_periods_between[] = $current_billing_period;

			if ( $to_timestamp - $from_timestamp < DAY_IN_SECONDS ) {
				break;
			}

			$counter++;
		}

		return $billing_periods_between;
	}

	public function provider_get_resource_billing_periods_between() {
		return array(
			// from and to timestamps exactly 1 month
			0 => array(
				'from_timestamp'   => strtotime( '2017-09-01 14:21:40' ),
				'to_timestamp'     => strtotime( '2017-10-01 14:21:40' ),
				'billing_period'   => 'month',
				'billing_interval' => 1,
				'expected_result' => array(
					array(
						'from_timestamp'  => strtotime( '2017-09-01 14:21:40' ),
						'to_timestamp'    => strtotime( '2017-10-01 14:21:40' ),
						'period_fraction' => 1
					)
				),
			),

			// from and to timstamps just over 1 month (20mins over)
			1 => array(
				'from_timestamp'   => strtotime( '2017-09-01 14:21:40' ),
				'to_timestamp'     => strtotime( '2017-10-01 14:40:40' ),
				'billing_period'   => 'month',
				'billing_interval' => 1,
				'expected_result' => array(
					array(
						'from_timestamp'  => strtotime( '2017-09-01 14:21:40' ),
						'to_timestamp'    => strtotime( '2017-10-01 14:40:40' ),
						'period_fraction' => 1
					)
				),
			),

			// ~1.5 billing periods found between the two dates
			2 => array(
				'from_timestamp'   => strtotime( '2017-09-14 14:21:40' ),
				'to_timestamp'     => strtotime( '2017-11-01 14:40:40' ),
				'billing_period'   => 'month',
				'billing_interval' => 1,
				'expected_result' => array(
					array(
						'from_timestamp'  => strtotime( '2017-09-14 14:21:40' ),
						'to_timestamp'    => strtotime( '2017-10-14 14:21:40' ),
						'period_fraction' => 1
					),
					array(
						'from_timestamp'  => strtotime( '2017-10-14 14:21:40' ),
						'to_timestamp'    => strtotime( '2017-11-01 14:40:40' ),
						'period_fraction' => 0.58
					),
				),
			),

			// If for some reason the renewal is triggered 1 hour early - the billing period should still be 1
			3 => array(
				'from_timestamp'   => strtotime( '2017-09-14 14:21:40' ),
				'to_timestamp'     => strtotime( '2017-10-14 12:40:40' ),
				'billing_period'   => 'month',
				'billing_interval' => 1,
				'expected_result' => array(
					array(
						'from_timestamp'  => strtotime( '2017-09-14 14:21:40' ),
						'to_timestamp'    => strtotime( '2017-10-14 12:40:40' ),
						'period_fraction' => 1
					),
				),
			),

			// If the billing period is only 15 days but the subscription renews monthly
			4 => array(
				'from_timestamp'   => strtotime( '2017-09-01 14:21:40' ),
				'to_timestamp'     => strtotime( '2017-09-16 12:40:40' ),
				'billing_period'   => 'month',
				'billing_interval' => 1,
				'expected_result' => array(
					array(
						'from_timestamp'  => strtotime( '2017-09-01 14:21:40' ),
						'to_timestamp'    => strtotime( '2017-09-16 12:40:40' ),
						'period_fraction' => 0.5
					),
				),
			),
		);
	}

	/**
	 * Make sure get_days_in_period() is calculating the number of days properly
	 *
	 *
	 * @dataProvider provider_get_resource_billing_periods_between
	 * @group billing_periods_between
	 */
	public function test_get_resource_billing_periods_between( $from_timestamp, $to_timestamp, $billing_period, $billing_interval, $expected_result ) {
		$resource_mock = $this->getMockBuilder( 'WCSR_Resource' )->setMethods( array( 'get_date_created' ) )->disableOriginalConstructor()->getMock();
		$this->assertEquals( $expected_result, $resource_mock->get_resource_billing_periods_between( $from_timestamp, $to_timestamp, $billing_period, $billing_interval ) );
	}