Generate a "Member Number" for WordPress users and show it on the PMPro account page.

generate_member_number.php

<?php

/*
	Member Numbers

	* Change the unique_alphanumeric_member_number function if your member number needs to be in a certain format.
	* Member numbers are generated when users are registered or when the membership account page is accessed for the first time.
*/

// randomize alphabetical string
function generate_random_alphabetic_string( $additional_seeds = 0 ) {
	$seed = 'abcdefghijklmnopqrstuvwxyz';
	for ( $i = 0; $i < $additional_seeds; $i++ ) {
		$seed = $seed . $seed;
	}
	return $seed;
}

// randomized alphanumeric string that accepts salting
function generate_random_alphanumeric_string( $salt = '' ) {
	return md5( AUTH_KEY . my_time_now_integer() . $salt . SECURE_AUTH_KEY );
}

// return time integer
function my_time_now_integer() {
	// for performance use hrtime if available.
	if ( function_exists( 'hrtime' ) ) {
		return hrtime( true );
	} else {
		return intval( microtime( true ) );
	}
}

function unique_alphanumeric_member_number( $user_id ) {
	$member_number = get_user_meta( $user_id, 'member_number', true );

	//if no member number, create one
	if ( empty( $member_number ) ) {
		$member_number_length = 10; // set length of member number, minimum 8.
		global $wpdb;

		//this code generates a string 10 characters long of numbers and letters
		while ( empty( $member_number ) ) {
			if ( $member_number_length < 8 ) {
				$member_number_length = 8;
			}
			$alphabetic_string = substr( generate_random_alphabetic_string( 3 ), 0, ( 6 - strlen( $user_id ) ) );
			$alphabetic_string = str_shuffle( $alphabetic_string );
			$scramble          = substr( generate_random_alphanumeric_string( $user_id ), 0, ( $member_number_length - strlen( $alphabetic_string ) - strlen( $user_id ) ) );
			$member_number     = $scramble . $alphabetic_string . $user_id;
			$check             = $wpdb->get_var( "SELECT meta_value FROM $wpdb->usermeta WHERE meta_value = '" . esc_sql( $member_number ) . "' LIMIT 1" );
			if ( $check || is_numeric( $member_number ) ) {
				$member_number = null;
			}
		}

		//save to user meta
		update_user_meta( $user_id, 'member_number', $member_number );

		// return $member_number;
	}
	return $member_number;
}

add_action( 'user_register', 'unique_alphanumeric_member_number' );


//Show it on the membership account page.
function pmpromn_pmpro_account_bullets_bottom() {
	if ( is_user_logged_in() ) {
		global $current_user;

		//get member number
		$member_number = get_user_meta( $current_user->ID, 'member_number', true );

		//if no number, generate one
		if ( empty( $member_number ) ) {
			$member_number = unique_alphanumeric_member_number( $current_user->ID );
		}

		//show it
		if ( ! empty( $member_number ) ) {
			?>
		<li><strong><?php _e( 'Member Number', 'pmpro' ); ?>:</strong> <?php echo $member_number; ?></li>
			<?php
		}
	}
}
add_action( 'pmpro_account_bullets_bottom', 'pmpromn_pmpro_account_bullets_bottom' );
add_action( 'pmpro_invoice_bullets_bottom', 'pmpromn_pmpro_account_bullets_bottom' );

//show member_number in confirmation emails
function pmpromn_pmpro_email_filter( $email ) {
	 global $wpdb;

	//only update admin confirmation emails
	if ( strpos( $email->template, 'checkout' ) !== false ) {
		if ( ! empty( $email->data ) && ! empty( $email->data['user_login'] ) ) {
			$user = get_user_by( 'login', $email->data['user_login'] );
			if ( ! empty( $user ) && ! empty( $user->ID ) ) {
				$member_number = get_user_meta( $user->ID, 'member_number', true );

				if ( ! empty( $member_number ) ) {
					$email->body = str_replace( '<p>Membership Level', '<p>Member Number:' . $member_number . '</p><p>Membership Level', $email->body );
				}
			}
		}
	}

	return $email;
}
add_filter( 'pmpro_email_filter', 'pmpromn_pmpro_email_filter', 30, 2 );