This is a really cool idea.
I don’t think part 2 should be handled inside WordPress: there are plenty of RSS to email providers. They’re going to be way better at that than a plugin (or theme) is likely to be.
BUT we can create RSS feeds.
Step one: set up a class to wrap everything up.
There are a few class constants and variables here — we’ll use them later. Just a singleton pattern.
<?php
class Per_User_Feeds
{
// Where we'll store the user cats
const META_KEY = '_per_user_feeds_cats';
// Nonce for the form fields
const NONCE = '_user_user_feeds_nonce';
// Taxonomy to use
const TAX = 'category';
// The query variable for the rewrite
const Q_VAR = 'puf_feed';
// container for the instance of this class
private static $ins = null;
// container for the terms allowed for this plugin
private static $terms = null;
public static function init()
{
add_action('plugins_loaded', array(__CLASS__, 'instance'));
}
public static function instance()
{
is_null(self::$ins) && self::$ins = new self;
return self::$ins;
}
}
Step two: add a field to the user profile pages (and save it)
You’ll need to hook into show_user_profile and edit_user_profile to do this. Spit out a nonce, a label, and the field. show_user_profile fires when users view their profile in the admin area. edit_user_profile fires when they edit another’s profile — this is how your admin user will go in an edit user’s categories.
<?php
class Per_User_Feeds
{
// snip snip
protected function __construct()
{
add_action('show_user_profile', array($this, 'field'));
add_action('edit_user_profile', array($this, 'field'));
}
public function field($user)
{
wp_nonce_field(self::NONCE . $user->ID, self::NONCE, false);
echo '<h4>', esc_html__('Feed Categories', 'per-user-feed'), '</h4>';
if($terms = self::get_terms())
{
$val = self::get_user_terms($user->ID);
printf('<select name="%1$s[]" id="%1$s" multiple="multiple">', esc_attr(self::META_KEY));
echo '<option value="">', esc_html__('None', 'per-user-feed'), '</option>';
foreach($terms as $t)
{
printf(
'<option value="%1$s" %3$s>%2$s</option>',
esc_attr($t->term_id),
esc_html($t->name),
in_array($t->term_id, $val) ? 'selected="selected"' : ''
);
}
echo '</select>';
}
}
}
That also introduces our first two helper methods:
get_user_terms, a simple wraper aroundget_user_metawith a call toapply_filters— let others modify things if they want!get_termsa wrapper aroundget_termswith a call toapply_filters.
Both of these are just convenience things. They also provide ways for other plugins/themes to hook in and modify things.
<?php
/**
* Get the categories available for use with this plugin.
*
* @uses get_terms
* @uses apply_filters
* @return array The categories for use
*/
public static function get_terms()
{
if(is_null(self::$terms))
self::$terms = get_terms(self::TAX, array('hide_empty' => false));
return apply_filters('per_user_feeds_terms', self::$terms);
}
/**
* Get the feed terms for a given user.
*
* @param int $user_id The user for which to fetch terms
* @uses get_user_meta
* @uses apply_filters
* @return mixed The array of allowed term IDs or an empty string
*/
public static function get_user_terms($user_id)
{
return apply_filters('per_user_feeds_user_terms',
get_user_meta($user_id, self::META_KEY, true), $user_id);
}
To save the fields, hook into personal_options_update (fires when user save their own profile) and edit_user_profile_update (fires when saving another user’s profile).
<?php
class Per_User_Feeds
{
// snip snip
protected function __construct()
{
add_action('show_user_profile', array($this, 'field'));
add_action('edit_user_profile', array($this, 'field'));
add_action('personal_options_update', array($this, 'save'));
add_action('edit_user_profile_update', array($this, 'save'));
}
// snip snip
public function save($user_id)
{
if(
!isset($_POST[self::NONCE]) ||
!wp_verify_nonce($_POST[self::NONCE], self::NONCE . $user_id)
) return;
if(!current_user_can('edit_user', $user_id))
return;
if(!empty($_POST[self::META_KEY]))
{
$allowed = array_map(function($t) {
return $t->term_id;
}, self::get_terms());
// PHP > 5.3: Make sure the items are in our allowed terms.
$res = array_filter(
(array)$_POST[self::META_KEY],
function($i) use ($allowed) {
return in_array($i, $allowed);
}
);
update_user_meta($user_id, self::META_KEY, array_map('absint', $res));
}
else
{
delete_user_meta($user_id, self::META_KEY);
}
}
}
Step three: provide a feed
Since this is very much a custom feed, we don’t want to hijack something like author feeds to get this done (though that’s an option!). Instead let’s add a rewrite: yoursite.com/user-feed/{{user_id}} will render the personalized user feed.
To add the rewrite we need to hook into init and use add_rewrite_rule. Since this uses a custom query variable to detect when we’re on a personalized user feed, we also need to hook into query_vars and our our custom variable so WordPress doesn’t ignore it.
<?php
class Per_User_Feeds
{
// snip snip
protected function __construct()
{
add_action('show_user_profile', array($this, 'field'));
add_action('edit_user_profile', array($this, 'field'));
add_action('personal_options_update', array($this, 'save'));
add_action('edit_user_profile_update', array($this, 'save'));
add_action('init', array($this, 'rewrite'));
add_filter('query_vars', array($this, 'query_var'));
}
// snip snip
public function rewrite()
{
add_rewrite_rule(
'^user-feed/(\d+)/?$',
'index.php?' . self::Q_VAR . '=$matches[1]',
'top'
);
}
public function query_var($v)
{
$v[] = self::Q_VAR;
return $v;
}
}
To actually render the feed, we’ll hook into template_redirect, look for our custom query var (bailing if we don’t find it), and hijack the global $wp_query with a personalized version.
I also hooked into wp_title_rss to modify the RSS title, which was a bit weird: it grabbed the first category and displayed the feed title as if looking at a single category.
<?php
class Per_User_Feeds
{
// snip snip
protected function __construct()
{
add_action('show_user_profile', array($this, 'field'));
add_action('edit_user_profile', array($this, 'field'));
add_action('personal_options_update', array($this, 'save'));
add_action('edit_user_profile_update', array($this, 'save'));
add_action('init', array($this, 'rewrite'));
add_filter('query_vars', array($this, 'query_var'));
add_action('template_redirect', array($this, 'catch_feed'));
}
// snip snip
public function catch_feed()
{
$user_id = get_query_var(self::Q_VAR);
if(!$user_id)
return;
if($q = self::get_user_query($user_id))
{
global $wp_query;
$wp_query = $q;
// kind of lame: anon function on a filter...
add_filter('wp_title_rss', function($title) use ($user_id) {
$title=" - " . __('User Feed', 'per-user-feed');
if($user = get_user_by('id', $user_id))
$title .= ': ' . $user->display_name;
return $title;
});
}
// maybe want to handle the "else" here?
// see do_feed_rss2
load_template( ABSPATH . WPINC . '/feed-rss2.php' );
exit;
}
}
To actually render the feed we rely on wp-includes/feed-rss2.php. You could replace this with something more custom, but why not be lazy?
There’s also a third helper method here: get_user_query. Same idea as the helpers above — abstract away some reusable functionality and provide hooks.
<?php
/**
* Get a WP_Query object for a given user.
*
* @acces public
* @uses WP_Query
* @return object WP_Query
*/
public static function get_user_query($user_id)
{
$terms = self::get_user_terms($user_id);
if(!$terms)
return apply_filters('per_user_feeds_query_args', false, $terms, $user_id);
$args = apply_filters('per_user_feeds_query_args', array(
'tax_query' => array(
array(
'taxonomy' => self::TAX,
'terms' => $terms,
'field' => 'id',
'operator' => 'IN',
),
),
), $terms, $user_id);
return new WP_Query($args);
}
Here is all of the above as a plugin. The plugin (and subsequently, this answer) requires PHP 5.3+ due to the use of anonymous functions.