# frozen_string_literal: true

class Trends::Statuses < Trends::Base
  PREFIX = 'trending_statuses'

  BATCH_SIZE = 100

  self.default_options = {
    threshold: 5,
    review_threshold: 3,
    score_halflife: 1.hour.freeze,
    decay_threshold: 0.3,
  }

  class Query < Trends::Query
    def filtered_for!(account)
      @account = account
      self
    end

    def filtered_for(account)
      clone.filtered_for!(account)
    end

    def to_arel
      scope = Status.joins(:trend).reorder(score: :desc)
      scope = scope.reorder(language_order_clause.desc, score: :desc) if preferred_languages.present?
      scope = scope.merge(StatusTrend.allowed) if @allowed
      scope = scope.not_excluded_by_account(@account).not_domain_blocked_by_account(@account) if @account.present?
      scope = scope.offset(@offset) if @offset.present?
      scope = scope.limit(@limit) if @limit.present?
      scope
    end

    private

    def language_order_clause
      Arel::Nodes::Case.new.when(StatusTrend.arel_table[:language].in(preferred_languages)).then(1).else(0)
    end

    def preferred_languages
      if @account&.chosen_languages.present?
        @account.chosen_languages
      else
        @locale
      end
    end
  end

  def register(status, at_time = Time.now.utc)
    add(status.proper, status.account_id, at_time) if eligible?(status.proper)
  end

  def add(status, _account_id, at_time = Time.now.utc)
    record_used_id(status.id, at_time)
  end

  def query
    Query.new(key_prefix, klass)
  end

  def refresh(at_time = Time.now.utc)
    # First, recalculate scores for statuses that were trending previously. We split the queries
    # to avoid having to load all of the IDs into Ruby just to send them back into Postgres
    Status.where(id: StatusTrend.select(:status_id)).includes(:status_stat, :account).reorder(nil).find_in_batches(batch_size: BATCH_SIZE) do |statuses|
      calculate_scores(statuses, at_time)
    end

    # Then, calculate scores for statuses that were used today. There are potentially some
    # duplicate items here that we might process one more time, but that should be fine
    Status.where(id: recently_used_ids(at_time)).includes(:status_stat, :account).reorder(nil).find_in_batches(batch_size: BATCH_SIZE) do |statuses|
      calculate_scores(statuses, at_time)
    end

    # Now that all trends have up-to-date scores, and all the ones below the threshold have
    # been removed, we can recalculate their positions
    StatusTrend.connection.exec_update('UPDATE status_trends SET rank = t0.calculated_rank FROM (SELECT id, row_number() OVER w AS calculated_rank FROM status_trends WINDOW w AS (PARTITION BY language ORDER BY score DESC)) t0 WHERE status_trends.id = t0.id')
  end

  def request_review
    StatusTrend.pluck('distinct language').flat_map do |language|
      score_at_threshold = StatusTrend.where(language: language, allowed: true).order(rank: :desc).where('rank <= ?', options[:review_threshold]).first&.score || 0
      status_trends      = StatusTrend.where(language: language, allowed: false).joins(:status).includes(status: :account)

      status_trends.filter_map do |trend|
        status = trend.status

        if trend.score > score_at_threshold && !status.trendable? && status.requires_review_notification?
          status.account.touch(:requested_review_at)
          status
        end
      end
    end
  end

  protected

  def key_prefix
    PREFIX
  end

  def klass
    Status
  end

  private

  def eligible?(status)
    status.public_visibility? && status.account.discoverable? && !status.account.silenced? && !status.account.sensitized? && status.spoiler_text.blank? && !status.sensitive? && !status.reply? && valid_locale?(status.language)
  end

  def calculate_scores(statuses, at_time)
    items = statuses.map do |status|
      expected  = 1.0
      observed  = (status.reblogs_count + status.favourites_count).to_f

      score = if expected > observed || observed < options[:threshold]
                0
              else
                ((observed - expected)**2) / expected
              end

      decaying_score = if score.zero? || !eligible?(status)
                         0
                       else
                         score * (0.5**((at_time.to_f - status.created_at.to_f) / options[:score_halflife].to_f))
                       end

      [decaying_score, status]
    end

    to_insert = items.filter { |(score, _)| score >= options[:decay_threshold] }
    to_delete = items.filter { |(score, _)| score < options[:decay_threshold] }

    StatusTrend.upsert_all(to_insert.map { |(score, status)| { status_id: status.id, account_id: status.account_id, score: score, language: status.language, allowed: status.trendable? || false } }, unique_by: :status_id) if to_insert.any?
    StatusTrend.where(status_id: to_delete.map { |(_, status)| status.id }).delete_all if to_delete.any?
  end
end
