Format the invoice number in UCM

custom_invoice_number.php

<?php

// this changes the invoice number format to a 7 digit string padded with 0's at the start
// example: instead of "Invoice #1" it will be "Invoice #0000007"
// upload this file to a new folder called 'includes/plugin_custom_invoice_number/custom_invoice_number.php'


if(!function_exists('custom_invoice_number')) {
	function custom_invoice_number( $customer_id ) {

		$invoice_number = module_config::c( 'invoice_incrementing_next', 1 );
		// see if there is an invoice number matching this one.
		$this_invoice_number = $invoice_number;
		do {
			$this_invoice_number_formatted = str_pad( $this_invoice_number, 7, '0', STR_PAD_LEFT );
			$invoices                      = get_multiple( 'invoice', array( 'name' => $this_invoice_number_formatted ) );
			//self::get_invoices(array('name'=>$invoice_prefix.$this_invoice_number)); //'customer_id'=>$customer_id,
			if ( ! $invoices ) {
				$invoice_number = $this_invoice_number;
				break;
			} else {
				// an invoice exists with this same number.
				// is it from last year?
				$this_invoice_number ++;
			}
		} while ( count( $invoices ) );
		module_config::save_config( 'invoice_incrementing_next', $invoice_number );

		return $this_invoice_number_formatted;
	}
}