Automatically downgrade a WooCommerce subscription (to a free, no-expiry variation) instead of expiring it

add-base-tier-option.php

<?php
/**
 * Add base tier option to Advanced tab of subscription product
 */
function doublee_subscription_product_advanced_settings() {
	$product = wc_get_product(get_the_id());
	if($product->get_type() === 'variable-subscription') {
		$variations = $product->get_available_variations();
		$variation_options = array();
		foreach ($variations as $variation) {
			$variation_id = $variation['variation_id'];
			$listing_level = $variation['attributes']['attribute_pa_subscription-level'];
			$term = get_term_by('slug', $listing_level, 'pa_subscription-level');
			$variation_options[$variation_id] = $term->name;
		}

		echo '<div class="options_group subscription_base_tier">';
		woocommerce_wp_select( array(
			'id'            => 'default_subscription_variation',
			'value'         => get_post_meta( get_the_id(), 'subscription_base_tier', true ),
			'wrapper_class' => '',
			'label'         => 'Subscription base tier',
			'description'   => 'Level to downgrade to when a subscription expires or is not renewed. This level should be free and have no expiry.',
			'options'       => $variation_options,
		) );
		echo '</div>';
	}
}
add_action('woocommerce_product_options_advanced', 'doublee_subscription_product_advanced_settings');


/**
 * Save the base tier option to postmeta of the subscription product
 * @param $post_id
 */
function doublee_save_subscription_product_advanced_settings($post_id) {
	if(isset($_POST['default_subscription_variation'])) {
		$base_tier = $_POST['default_subscription_variation'];
		update_post_meta($post_id, 'subscription_base_tier', $base_tier);
	}
}
add_action('woocommerce_process_product_meta',  'doublee_save_subscription_product_advanced_settings', 10, 1);

auto-downgrade.php

<?php
/**
 * Automatically downgrade a subscription to the free, no-expiry tier when:
 * - A subscription expires
 * - Renewal payment fails
 * - A subscription with manual renewal payment is not renewed
 *
 * @param $subscription
 */
function doublee_downgrade_subscription_to_base_tier($subscription) {

	// Set subscription back to active
	$subscription->update_status('active');

	// Get the product associated with the subscription
	$items = $subscription->get_items();
	$product_id = $items[array_key_first($items)]->get_product_id();

	// Get the base tier variation from the subscription product's meta
	$base_tier_variation_id = get_post_meta($product_id, 'subscription_base_tier', true);

	// Get the full variation array
	$product = wc_get_product($product_id);
	$all_variations = $product->get_available_variations();
	$base_tier_variation_details = doublee_search_nested_associative_array('variation_id', $base_tier_variation_id, $all_variations);

	// Get the details we need from the base variation array
	$subscription_level_slug = $base_tier_variation_details['attributes']['attribute_pa_subscription-level'];
	$subscription_level_term = get_term_by('slug', $subscription_level_slug, 'pa_subscription-level');
	$subscription_level_name = $subscription_level_term->name;

	// Get the subscription order line item to update
	$items = $subscription->get_items();
	$order_item_index = array_key_first($items);

	// Remove it
	$subscription->remove_item($order_item_index);

	// Replace it with a new item of the base tier
	$new_order_item = new WC_Order_Item_Product();
	$new_order_item->set_product($product);
	$new_order_item->set_name($product->get_name() . ' - ' . $subscription_level_name);
	$new_order_item->set_variation_id($base_tier_variation_id);
	$new_order_item->set_quantity(1);
	$new_order_item->set_subtotal($base_tier_variation_details['display_regular_price']);
	$new_order_item->set_total($base_tier_variation_details['display_regular_price']);
	$new_order_item->save();
	$subscription->add_item($new_order_item);

	// Update the subscription renewal date and clear the end date
	$dates_to_update = array();
	$dates_to_update['end'] = '';
	$dates_to_update['next_payment'] = date('Y-m-d H:i:s', strtotime('+1 year'));
	$subscription->update_dates($dates_to_update);

	// Update the recurring total of the subscription
	$subscription->calculate_totals();

	// Get the listing post ID from the subscription's post meta
	$listing_id = doublee_get_listing_for_order_or_subscription($subscription->get_id());

	// Update its listing_level taxonomy terms
	$new_level = get_term_by('slug', $subscription_level_slug, 'listing_level');
	wp_set_object_terms($listing_id, $new_level->term_id, 'listing_level');

	// Update its listing_level post meta
	update_post_meta($listing_id, '_listing_level', $subscription_level_slug);
}


/**
 * Trigger downgrade after expiry
 * Note: Added plugin mod to add custom action hook woocommerce_after_subscription_status_updated to ensure the notes are added in the right order
 * // TODO: Check if that mod can be added to WooCommerce core instead and submit a pull request if it can
 * @param $subscription
 * @param $to
 * @param $from
 */
function doublee_downgrade_on_subscription_expiry($subscription, $to, $from) {
	if($to == 'expired') {
		// Perform downgrade
		doublee_downgrade_subscription_to_base_tier($subscription);

		// Add CMS notes
		$subscription->add_order_note('Status changed from Expired to ' . ucfirst($subscription->get_status()));
		$subscription->add_order_note('Subscription automatically downgraded to base tier and reactivated, due to expiry or non-renewal.', 0, false);
	}
}
add_action('woocommerce_after_subscription_status_updated', 'doublee_downgrade_on_subscription_expiry', 5, 3);


/**
 * Trigger downgrade on failed renewal payment
 *
 * @param $subscription
 */
function doublee_downgrade_on_renewal_failure($subscription) {

	// Perform downgrade
	doublee_downgrade_subscription_to_base_tier($subscription);

	// Add CMS note
	$subscription->add_order_note('Subscription automatically downgraded to base tier and reactivated, due to expiry or non-renewal.', 0, false);
}
add_action('woocommerce_subscription_renewal_payment_failed', 'doublee_downgrade_on_renewal_failure', 10, 1);

class-wc-subscription.php

<?php

/**
 * Handle the status transition.
 */
protected function status_transition() {
	// Use local copy of status transition value.
	$status_transition = $this->status_transition;

	// If we're not currently in the midst of a status transition, bail early.
	if ( ! $status_transition ) {
		return;
	}

	// MOD: If the statuses are the same, don't do anything.
	// doublee_downgrade_subscription_to_base_tier triggers an "Active to Active" order note because it triggers a save() within some of its methods,
	// which is necessary for the updates that that function makes, but it also happens to trigger status_transition().
	if($status_transition['from'] === $status_transition['to']) {
		return;
	}

	try {
		do_action( "woocommerce_subscription_status_{$status_transition['to']}", $this );

		if ( ! empty( $status_transition['from'] ) ) {
			$transition_note = sprintf(
				/* translators: 1: old subscription status 2: new subscription status */
				__( 'Status changed from %1$s to %2$s.', 'woocommerce-subscriptions' ),
				wcs_get_subscription_status_name( $status_transition['from'] ),
				wcs_get_subscription_status_name( $status_transition['to'] )
			);

			do_action( "woocommerce_subscription_status_{$status_transition['from']}_to_{$status_transition['to']}", $this );

			// Trigger a hook with params we want.
			do_action( 'woocommerce_subscription_status_updated', $this, $status_transition['to'], $status_transition['from'] );

			// Trigger a hook with params matching WooCommerce's 'woocommerce_order_status_changed' hook so functions attached to it can be attached easily to subscription status changes.
			do_action( 'woocommerce_subscription_status_changed', $this->get_id(), $status_transition['from'], $status_transition['to'], $this );
		} else {
			/* translators: %s: new order status */
			$transition_note = sprintf( __( 'Status set to %s.', 'woocommerce-subscriptions' ), wcs_get_subscription_status_name( $status_transition['to'] ) );
		}

		// Note the transition occurred.
		$this->add_order_note( trim( "{$status_transition['note']} {$transition_note}" ), 0, $status_transition['manual'] );

		// MOD: Custom action hook for some of our custom subscription processing
		do_action( 'woocommerce_after_subscription_status_updated', $this, $status_transition['to'], $status_transition['from'] );

	} catch ( Exception $e ) {
		$logger = wc_get_logger();
		$logger->error(
			sprintf( 'Status transition of subscription #%d errored!', $this->get_id() ),
			array(
				'order' => $this,
				'error' => $e,
			)
		);
		$this->add_order_note( __( 'Error during subscription status transition.', 'woocommerce-subscriptions' ) . ' ' . $e->getMessage() );
	}

	// This has run, so reset status transition variable
	$this->status_transition = false;
}

utilities.php

<?php
/**
 * Utility function to find a key => value pair in a nested associative array and then return that array
 * @param $key
 * @param $value
 * @param $haystack
 *
 * @return false|mixed
 */
function doublee_search_nested_associative_array($key, $value, $haystack) {

	foreach($haystack as $index => $inner_array) {
		if($inner_array[$key] == $value) {
			return $inner_array;
		}
	}

	return false;
}