Twitter-like Trending Topics App Backend - PHP Example

redis_hot_topics.php

<?php

// @see https://medium.com/@elhardoum/2a442e04bb2f

function get_redis() : \Redis {
    static $redis;

    if ( null === $redis ) {
        $redis = new \Redis();
        $redis->connect('0.0.0.0', 6379);
        register_shutdown_function([$redis, 'close']);
    }

    return $redis;
}

function boost_topic(string $setId, string $member, int $increment_by=1) : void
{
    // create a set for 5 minutes, with a TTL of 1 hour
    // reason: cannot expire set members without expiring the whole set
    $setId .= ':' . date('H.') . round(date('i')/5);

    // increment set member score
    get_redis()->zincrby($setId, $increment_by, $member);

    if ( get_redis()->ttl($setId) == -1 ) // is this a new set? if so, set TTL to 60min to we don't keep stale data
        get_redis()->expire($setId, 3600);
}

function get_top_topics(string $setId, int $limit=10) : array
{
    $items = [];

    // query all sets created in the past 30min
    if ( $sets = get_redis()->keys("{$setId}:*") ) {
        $meta = [ 'withscores' => true, 'limit' => [0, $limit] ];

        // begin transaction
        get_redis()->multi();

        foreach ( $sets as $set ) {
            // get top N (=$limit) winners of each set and merge them together
            get_redis()->zrevrangebyscore($set, '+inf', '-inf', $meta);
        }

        // commit transaction
        $result = get_redis()->exec();

        foreach ( $sets as $i => $set ) {
            if ( $list = array_map('intval', $result[$i] ?? []) ) {
                foreach ( $list as $k=>$v ) {
                    $items[$k] = ($items[$k] ?? 0) + $v;
                }
            }
        }

        arsort($items);

        // return top winners
        $items = array_slice($items, 0, $limit);
    }

    return $items;
}

// boost a topic's score
boost_topic('hot-topics', 'Caturday');
boost_topic('hot-topics', 'Feline');
boost_topic('hot-topics', 'Thursday');

// boost a topic's score by 2 points
boost_topic('hot-topics', 'Feline', 2);


// get a list of top 2 trends
get_top_topics('hot-topics', 2); // [ 'Feline' => 3, 'Caturday' => 1 ]