feed.rb

require 'blue_factory/errors'
require 'rainbow'
require 'time'

require_relative '../models/feed_post'

class Feed
  DEFAULT_LIMIT = 50
  MAX_LIMIT = 100

  # any unique number to use as a key in the database
  def feed_id
    raise NotImplementedError
  end

  def post_matches?(post)
    raise NotImplementedError
  end

  # name of your feed, e.g. "What's Hot"
  def display_name
    raise NotImplementedError
  end

  # (optional) description of the feed, e.g. "Top trending content from the whole network"
  def description
    nil
  end

  # (optional) path of the feed avatar file
  def avatar_file
    nil
  end

  # (optional) should posts be added to the feed from the firehose?
  def is_updating?
    true
  end

  # if the feed matches posts using keywords/regexps, highlight these keywords in the passed text
  def colored_text(text)
    text
  end

  def get_posts(params)
    limit = check_query_limit(params)
    query = FeedPost.where(feed_id: feed_id).joins(:post).select('posts.repo, posts.rkey, feed_posts.time, post_id')
      .order('feed_posts.time DESC, post_id DESC').limit(limit)

    if params[:cursor].to_s != ""
      time, last_id = parse_cursor(params)
      query = query.where("feed_posts.time < ? OR (feed_posts.time = ? AND post_id < ?)", time, time, last_id)
    end

    posts = query.to_a
    last = posts.last

    cursor = last && sprintf('%.06f', last.time.to_f) + ':' + last.post_id.to_s

    { cursor: cursor, posts: posts.map { |p| 'at://' + p.repo + '/app.bsky.feed.post/' + p.rkey }}
  end

  # Use this version of the method when enable_unsafe_auth is set to true in app/config.rb.
  # This method is called with the DID of the user viewing the feed decoded from the auth header.
  #
  # Important: BlueFactory does not verify auth signatures of the JWT token at the moment,
  # which means that anyone can easily spoof the DID in the header - do not use for anything critical!
  #
  # def get_posts(params, visitor_did)
  #   # You can use this DID to e.g.:
  #   # 1) Provide a personalized feed:
  #
  #   user = User.find_by(did: visitor_did)
  #   raise BlueFactory::AuthorizationError unless user
  #   build_feed_for_user(user)
  #
  #   # 2) Only allow whitelisted users to view the feed and show it as empty to others:
  #   if visitor_did == BlueFactory.publisher_did || ALLOWED_USERS.include?(visitor_did)
  #     get_feed_posts(params)
  #   else
  #     { posts: [] }
  #   end
  #
  #   # 3) Ban some users from accessing the feed:
  #   # (note: you can return a custom error message that will be shown in the error banner in the app)
  #   if BANNED_USERS.include?(visitor_did)
  #     raise BlueFactory::AuthorizationError, "You shall not pass!"
  #   else
  #     get_feed_posts(params)
  #   end
  #
  #   # 4) Collect feed analytics (please take the privacy of your users into account)
  #   Stats.count_visit(visitor_did)
  # end


  private

  def check_query_limit(params)
    if params[:limit]
      limit = params[:limit].to_i
      (limit < 0) ? 0 : [limit, MAX_LIMIT].min
    else
      DEFAULT_LIMIT
    end
  end

  def parse_cursor(params)
    parts = params[:cursor].split(':')

    if parts.length != 2 || parts[0] !~ /^\d+(\.\d+)?$/ || parts[1] !~ /^\d+$/
      raise BlueFactory::InvalidRequestError.new("Malformed cursor")
    end

    sec = parts[0].to_i
    usec = (parts[0].to_f * 1_000_000).to_i % 1_000_000
    time = Time.at(sec, usec)

    last_id = parts[1].to_i

    [time, last_id]
  end
end