Discounts when purchasing multiple levels with PMPro MMPU

my_pmpro_checkout_level_discounts.php

/**
 * Discounts when purchasing multiple levels with PMPro MMPU
 * 
 * 1. Add this to a custom plugin or code snippet.
 * 2. Adjust the discount_levels array.
 * 3. Adjust the logic for when the price is changed and how much.
 * 4. Make sure to remove the billing_amount lines if you don't have recurring billing.
 */
function my_pmpro_checkout_level_discounts( $level ) {
	$discount_levels = array(1, 2, 3, 4, 5, 6, 7, 8, 9, 10 );
	
	if ( isset( $_REQUEST['level'] ) ) {
		$level_ids = array_map( 'intval', explode( "+", preg_replace( "[^0-9\+]", "", $_REQUEST['level'] ) ) );
		
		$count = count( array_intersect( $discount_levels, $level_ids ) );
		
		if ( $count > 1 ) {
			// $5 off for the second level
			$level->initial_payment = $level->initial_payment - 5;
			$level->billing_amount = $level->billing_amount - 5;
		}
		
		if ( $count > 2 ) {
			// $2 off for each additional level past 2
			$level->initial_payment = $level->initial_payment - ($count - 1)*2;
			$level->billing_amount = $level->billing_amount - ($count - 1)*2;
		}
		
		// make sure we're > $5
		$level->initial_payment = max( 5, $level->initial_payment );
		$level->billing_amount = max( 5, $level->billing_amount );
		
		// make sure we're formatted correctly
		$level->initial_payment = pmpro_round_price( $level->initial_payment );
		$level->billing_amount = pmpro_round_price( $level->billing_amount );
	}
	
	return $level;
}
add_filter( 'pmpro_checkout_level', 'my_pmpro_checkout_level_discounts' );