discourse/lib/score_calculator.rb

class ScoreCalculator

  def self.default_score_weights
    {
      reply_count: 5,
      like_score: 15,
      incoming_link_count: 5,
      bookmark_count: 2,
      avg_time: 0.05,
      reads: 0.2
    }
  end

  def initialize(weightings=nil)
    @weightings = weightings || ScoreCalculator.default_score_weights
  end

  # Calculate the score for all posts based on the weightings
  def calculate(opts=nil)
    update_posts_score(opts)
    update_posts_rank(opts)
    update_topics_rank(opts)
    update_topics_percent_rank(opts)
  end


  private

  def update_posts_score(opts)
    limit = 20000

    components = []
    @weightings.each_key { |k| components << "COALESCE(posts.#{k}, 0) * :#{k}" }
    components = components.join(" + ")

    builder = SqlBuilder.new <<SQL
       UPDATE posts p
        SET score = x.score
       FROM (
        SELECT posts.id, #{components} as score FROM posts
        join topics on posts.topic_id = topics.id
        /*where*/
        limit #{limit}
       ) AS x
       WHERE x.id = p.id
SQL

    builder.where("posts.score IS NULL OR posts.score <> #{components}", @weightings)

    filter_topics(builder, opts)

    while builder.exec.cmd_tuples == limit
    end
  end

  def update_posts_rank(opts)
    limit = 20000

    builder = SqlBuilder.new <<SQL
UPDATE posts
SET percent_rank = X.percent_rank
FROM (
  SELECT posts.id, Y.percent_rank
  FROM posts
  JOIN (
    SELECT id, percent_rank()
                 OVER (PARTITION BY topic_id ORDER BY SCORE DESC) as percent_rank
    FROM posts
   ) Y ON Y.id = posts.id
   JOIN topics ON posts.topic_id = topics.id
  /*where*/
  LIMIT #{limit}
) AS X
WHERE posts.id = X.id
SQL

    builder.where("posts.percent_rank IS NULL OR Y.percent_rank <> posts.percent_rank")

    filter_topics(builder, opts)

    while builder.exec.cmd_tuples == limit
    end

  end

  def update_topics_rank(opts)
    builder = SqlBuilder.new("UPDATE topics AS topics
              SET has_summary = (topics.like_count >= :likes_required AND
                                 topics.posts_count >= :posts_required AND
                                 x.max_score >= :score_required),
                  score = x.avg_score
              FROM (SELECT p.topic_id,
                           MAX(p.score) AS max_score,
                           AVG(p.score) AS avg_score
                    FROM posts AS p
                    GROUP BY p.topic_id) AS x
                    /*where*/")

    builder.where("x.topic_id = topics.id AND
                        (
                          (topics.score <> x.avg_score OR topics.score IS NULL) OR
                          (topics.has_summary IS NULL OR topics.has_summary <> (
                            topics.like_count >= :likes_required AND
                            topics.posts_count >= :posts_required AND
                            x.max_score >= :score_required
                          ))
                        )
  ",
              likes_required: SiteSetting.summary_likes_required,
              posts_required: SiteSetting.summary_posts_required,
              score_required: SiteSetting.summary_score_threshold)


    filter_topics(builder, opts)

    builder.exec
  end

  def update_topics_percent_rank(opts)

    builder = SqlBuilder.new("UPDATE topics SET percent_rank = x.percent_rank
          FROM (SELECT id, percent_rank()
                OVER (ORDER BY SCORE DESC) as percent_rank
                FROM topics) AS x
                /*where*/")

    builder.where("x.id = topics.id AND (topics.percent_rank <> x.percent_rank OR topics.percent_rank IS NULL)")

    filter_topics(builder, opts)

    builder.exec
  end


  def filter_topics(builder, opts)
    return builder unless opts

    if min_topic_age = opts[:min_topic_age]
      builder.where("topics.bumped_at > :bumped_at ",
                 bumped_at: min_topic_age)
    end
    if max_topic_length = opts[:max_topic_length]
      builder.where("topics.posts_count < :max_topic_length",
                 max_topic_length: max_topic_length)
    end

    builder
  end

end