Link Paid Memberships Pro discount codes to affiliate accounts from another plugin/service.

pmpro_ld2aff.php

/*
	Link discount codes to affiliates.
*/
//this is the parameter we're looking for to find affiliates... based on which plugin/etc you are using
define('PMPRO_LDC2AFF_KEY', 'wpam_id');		//Affiliates Manager Plugin
//define('PMPRO_LDC2AFF_KEY', 'pa');			//WordPress Lightweight Affiliates
//define('PMPRO_LDC2AFF_KEY', 'ref');			//AffiliateWP

//helper function to get the values from options and make sure they are an array
function pmpro_ld2aff_getOptions() {
	$d2a = get_option('pmpro_ldc2aff', array());

	if(!is_array($d2a))
		$d2a = array();

	return $d2a;
}

//helper function to add a discount code/affiliate pair
function pmpro_ldc2aff_updateCode($code_id, $affiliate) {
	$d2a = pmpro_ld2aff_getOptions();

	if(empty($affiliate) && !empty($d2a[$code_id])) {
		unset($d2a[$code_id]);
		update_option('pmpro_ldc2aff', $d2a, 'no');
	} elseif(!empty($affiliate)) {
		$d2a[$code_id] = $affiliate;
		update_option('pmpro_ldc2aff', $d2a, 'no');
	}
}

//helper to get a discount code from an affiliate
function pmpro_ldc2aff_getCodeByAffiliate($affiliate) {
	$d2a = pmpro_ld2aff_getOptions();

	return array_search($affiliate, $d2a);
}

//helper get an affiliate id from a discount code
function pmpro_ldc2aff_getAffiliateByCode($code_id) {
	$d2a = pmpro_ld2aff_getOptions();

	if(isset($d2a[$code_id]))
		return $d2a[$code_id];
	else
		return "";
}

//on init we try to sync the affiliate id and discount code
function pmpro_ldc2aff_init() {
	global $wpdb;

	//if this isn't set, we can't work
	if(!defined('PMPRO_LDC2AFF_KEY'))
		return;

	//make sure PMPro is active
	if(!defined('PMPRO_VERSION'))
		return;

	//might want to check if a specific affiliate plugin is also running

	//affiliate id? set discount code
	if(!empty($_REQUEST[PMPRO_LDC2AFF_KEY])) {
		//bail if another discount code is already set
		if(!empty($_REQUEST['discount_code']))
			return;		

		//otherwise, let's figure out the code to use
		$affiliate = sanitize_text_field($_REQUEST[PMPRO_LDC2AFF_KEY]);
		$code_id = pmpro_ldc2aff_getCodeByAffiliate($affiliate);

		if(!empty($code_id)) {
			$code = $wpdb->get_var("SELECT `code` FROM $wpdb->pmpro_discount_codes WHERE id ='" . intval($code_id) . "' LIMIT 1");
			$_REQUEST['discount_code'] = $code;
			$_GET['discount_code'] = $code;
			$_POST['discount_code'] = $code;
		}
	}

	//discount code? set affiliate id
	if(!empty($_REQUEST['discount_code'])) {
		$code = sanitize_text_field($_REQUEST['discount_code']);
		$code_id = $wpdb->get_var("SELECT id FROM $wpdb->pmpro_discount_codes WHERE `code` = '" . esc_sql($code) . "' LIMIT 1");
		if(!empty($code_id)) {
			$affiliate = pmpro_ldc2aff_getAffiliateByCode($code_id);
			$_REQUEST[PMPRO_LDC2AFF_KEY] = $affiliate;
			$_GET[PMPRO_LDC2AFF_KEY] = $affiliate;
			$_POST[PMPRO_LDC2AFF_KEY] = $affiliate;
		}
	}

}
add_action('init', 'pmpro_ldc2aff_init', 1);

//show options on discont code page
function pmpro_ldc2aff_pmpro_discount_code_after_settings($code_id) {
	$affiliate = pmpro_ldc2aff_getAffiliateByCode($code_id);
?>
<hr />
<h3>Affiliate</h3>
<p>Link this discount code to an affiliate. Currently monitoring the '<?php echo PMPRO_LDC2AFF_KEY;?>' parameter. When the affiliate ID is set, this discount code will be defaulted to be used at checkout, and when a discount code is used the affiliate ID will be set.</p>
<p><label for="pmpro_ldc2aff_affiliate">Affiliate ID:</label><input type="text" id="pmpro_ldc2aff_affiliate" name="pmpro_ldc2aff_affiliate" value="<?php echo esc_attr($affiliate);?>" /></p>
<hr />
<?php
}
add_action('pmpro_discount_code_after_settings', 'pmpro_ldc2aff_pmpro_discount_code_after_settings');

//save options when code is updated
function pmpro_ldc2aff_pmpro_save_discount_code($code_id) {
	if($code_id < 1)
		return;

	$affiliate = sanitize_text_field($_REQUEST['pmpro_ldc2aff_affiliate']);

	pmpro_ldc2aff_updateCode($code_id, $affiliate);
}
add_action('pmpro_save_discount_code', 'pmpro_ldc2aff_pmpro_save_discount_code');

//delete options when code is deleted
function pmpro_ldc2aff_pmpro_delete_discount_code($code_id) {
	if($code_id < 1)
		return;

	pmpro_ldc2aff_updateCode($code_id, false);
}
add_action('pmpro_delete_discount_code', 'pmpro_ldc2aff_pmpro_delete_discount_code');

Forked here with some fixes: https://gist.github.com/ideadude/a10279629c2f312f18b90804ce9cd369

FYI when we turned our Stranger Studios GitHub account into an "organization", I lost the ability to edit these old gists.