wordpress-discourse-group-sync.php

<?php
/**
 * Sync Groups from WordPress to Discourse
 * 
 * First creates 'groups' meta_key (which should be customized to your needs)
 * Then it monitors for changes in the 'groups' meta_value and connects to Discourse API to sync groups
 * 
 * WordPress References
 * https://core.trac.wordpress.org/browser/tags/3.9/src/wp-includes/meta.php?order=name#L235
 * http://wordpress.stackexchange.com/questions/16835/how-to-hook-update-post-meta-and-delete-post-meta
 * Genesis theme /lib/admin/user-meta.php
 *
 * Discourse References
 * https://github.com/discoursehosting/discourse-api-php/blob/master/lib/DiscourseAPI.php
 * https://github.com/discourse/wp-discourse/blob/master/wp-discourse.php#L354
 * https://meta.discourse.org/t/add-users-to-and-remove-from-groups-via-api/15093/2?u=adamcapriola
 * 
 */

//
// Add group fields to user profile
//
add_action( 'show_user_profile', 'ac_user_groups_fields', 9 );
add_action( 'edit_user_profile', 'ac_user_groups_fields', 9 );

function ac_user_groups_fields( $user ) {

	// The group name here is "cats"

	if ( ! current_user_can( 'edit_users', $user->ID ) )
		return false;

	$groups = get_user_meta( $user->ID, 'groups', true );
	if ( empty( $groups ) ) $groups = array( 'cats' => 0 );

	?>
	<h3>Groups</h3>
	<table class="form-table">
		<tbody>
			<tr>
				<th scope="row" valign="top">Groups</th>
				<td>
					<input id="groups[cats]" name="groups[cats]" type="checkbox" value="1" <?php checked( $groups['cats'] ); ?> />
					<label for="groups[cats]">Cats</label><br />
					<input id="groups[registered]" name="groups[registered]" type="hidden" value="1">
				</td>
			</tr>
		</tbody>
	</table>
	<?php

}

//
// Save custom user profile fields
//
add_action( 'personal_options_update',  'ac_user_groups_save' );
add_action( 'edit_user_profile_update', 'ac_user_groups_save' );

function ac_user_groups_save( $user_id ) {

	if ( ! current_user_can( 'edit_users', $user_id ) )
		return;

	if ( ! isset( $_POST['groups'] ) || ! is_array( $_POST['groups'] ) )
		return;

	$groups = $_POST['groups'];

	update_user_meta( $user_id, 'groups', $groups );

}

//
// Listen for changes to groups
//
add_action( 'added_user_meta', 'ac_discourse_groups_sync', 10, 4 );
add_action( 'updated_user_meta', 'ac_discourse_groups_sync', 10, 4 );

function ac_discourse_groups_sync( $meta_id, $user_id, $meta_key, $meta_value ) {

	if ( $meta_key == 'groups' ) {

		$userdata = get_userdata( $user_id );
		$username = $userdata->user_login;

		// If user is a member of the group, try to add them on Discourse, otherwise remove
		if ( ! empty( $meta_value['cats'] ) ) $action = 'add';
		else $action = 'remove';

		//
		// Define variables
		//
		$discourse_url = 'http://discourse.example.com'; // Note: No trailing slash!
		$api_key = 'meow'; // API key
		$api_username = 'system'; // API username (should be an admin)

		$group_name = 'cats'; // Name of group
		$group_number = '43'; // Need to run browser console and log network to find this

		//
		// Get usernames of all group members
		//

		// URL
		$url = sprintf(
			'%s/groups/%s/members.json',
			$discourse_url,
			$group_name
		);

		// cURL
		$ch = curl_init();
		curl_setopt( $ch, CURLOPT_URL, $url );
		curl_setopt( $ch, CURLOPT_RETURNTRANSFER, 1 );
		$body = curl_exec( $ch );
		curl_close( $ch );

		// Intrepret results
		$json = json_decode( $body, true );

		$usernames = array();	
		foreach ( $json as $key => $value ) $usernames[] = $value['username'];

		// Probably need some kind of error check
		// if ( empty( $usernames ) ) {}

		//
		// Add or remove username from array
		//

		if ( $action == 'add' && !in_array( $username, $usernames ) ) {

			$usernames[] = $username;

		}

		elseif ( $action == 'remove' && in_array( $username, $usernames ) ) {

			$key = array_search( $username, $usernames);
			unset( $usernames[$key] );

		}

		else {

			return;

		}

		// Prepare usernames for API call
		if ( !empty( $usernames ) ) $usernames = implode ( ',', $usernames );

		//
		// Manipulate group members
		//

		// URL
		$url = sprintf(
			'%s/admin/groups/%s?api_key=%s&api_username=%s',
			$discourse_url,
			$group_number,
			$api_key,
			$api_username
		);

		// Parameters
		$paramArray = array(
			'group[name]' => $group_name,
			'group[alias_level]' => 99,
			'group[visible]' => 'true',
			'group[usernames]' => $usernames
		);

		// cURL
		$ch = curl_init();
		curl_setopt( $ch, CURLOPT_URL, $url );
		curl_setopt( $ch, CURLOPT_POSTFIELDS, http_build_query( $paramArray ) );
		curl_setopt( $ch, CURLOPT_RETURNTRANSFER, 1 );
		curl_setopt( $ch, CURLOPT_CUSTOMREQUEST, 'PUT' );
		$body = curl_exec( $ch );
		curl_close( $ch );

		// Intrepret results
		$json = json_decode( $body, true );

		// Probably need some kind of error check
		// if ( empty( $json ) || $json['success'] != 'OK' ) {}

	}

}

Thanks for your share!