mastodon/app/models/trending_tags.rb

# frozen_string_literal: true

class TrendingTags
  KEY                  = 'trending_tags'
  EXPIRE_HISTORY_AFTER = 7.days.seconds
  EXPIRE_TRENDS_AFTER  = 1.day.seconds
  THRESHOLD            = 5

  class << self
    def record_use!(tag, account, at_time = Time.now.utc)
      return if disallowed_hashtags.include?(tag.name) || account.silenced? || account.bot?

      increment_historical_use!(tag.id, at_time)
      increment_unique_use!(tag.id, account.id, at_time)
      increment_vote!(tag.id, at_time)
    end

    def get(limit)
      key     = "#{KEY}:#{Time.now.utc.beginning_of_day.to_i}"
      tag_ids = redis.zrevrange(key, 0, limit - 1).map(&:to_i)
      tags    = Tag.where(id: tag_ids).to_a.map { |tag| [tag.id, tag] }.to_h
      tag_ids.map { |tag_id| tags[tag_id] }.compact
    end

    private

    def increment_historical_use!(tag_id, at_time)
      key = "activity:tags:#{tag_id}:#{at_time.beginning_of_day.to_i}"
      redis.incrby(key, 1)
      redis.expire(key, EXPIRE_HISTORY_AFTER)
    end

    def increment_unique_use!(tag_id, account_id, at_time)
      key = "activity:tags:#{tag_id}:#{at_time.beginning_of_day.to_i}:accounts"
      redis.pfadd(key, account_id)
      redis.expire(key, EXPIRE_HISTORY_AFTER)
    end

    def increment_vote!(tag_id, at_time)
      key      = "#{KEY}:#{at_time.beginning_of_day.to_i}"
      expected = redis.pfcount("activity:tags:#{tag_id}:#{(at_time - 1.day).beginning_of_day.to_i}:accounts").to_f
      expected = 1.0 if expected.zero?
      observed = redis.pfcount("activity:tags:#{tag_id}:#{at_time.beginning_of_day.to_i}:accounts").to_f

      if expected > observed || observed < THRESHOLD
        redis.zrem(key, tag_id.to_s)
      else
        score = ((observed - expected)**2) / expected
        redis.zadd(key, score, tag_id.to_s)
      end

      redis.expire(key, EXPIRE_TRENDS_AFTER)
    end

    def disallowed_hashtags
      return @disallowed_hashtags if defined?(@disallowed_hashtags)

      @disallowed_hashtags = Setting.disallowed_hashtags.nil? ? [] : Setting.disallowed_hashtags
      @disallowed_hashtags = @disallowed_hashtags.split(' ') if @disallowed_hashtags.is_a? String
      @disallowed_hashtags = @disallowed_hashtags.map(&:downcase)
    end

    def redis
      Redis.current
    end
  end
end