Class that handles the PostgreSQL full text search for railscasts.com

episode_search.rb

class EpisodeSearch
  attr_reader :ability, :options
  delegate :sanitize, to: Episode

  def initialize(ability, options = {})
    @ability = ability
    @options = options.dup
  end

  def tag
    @tag ||= Tag.find_by_id(options[:tag_id]) if options[:tag_id].present?
  end

  def episodes(paginate = true)
    episodes = (tag ? tag.episodes : Episode).accessible_by(ability).where(type_conditions)
    episodes = episodes.paginate(page: page, per_page: per_page) if paginate
    if options[:search]
      episodes = episodes.where(search_conditions(options[:search])).order(order_clause)
    else
      episodes = episodes.recent
    end
    episodes
  end

  def similar_episodes(episode)
    episodes(false).limit(5).where(search_conditions(episode.name, "OR")).where("episodes.id != ?", episode.id)
  end

  def type_conditions
    case options[:type]
    when "free" then {pro: false, revised: false}
    when "pro" then {pro: true, revised: false}
    when "revised" then {revised: true}
    else {}
    end
  end

  def search_conditions(query, join = "AND")
    query.split(/\s+/).map do |word|
      '(' + word_search_conditions(word).join(' OR ') + ')'
    end.join(" #{join} ")
  end

  def word_search_conditions(word)
    %w[name description notes].map do |col|
      "to_tsvector('english', episodes.#{col}) @@ plainto_tsquery(#{sanitize(word)})"
    end + ["episodes.position::varchar = #{sanitize(word)}"]
  end

  def order_clause
    (search_order_clauses + extra_order_clauses).join(" + ") + " desc"
  end

  def search_order_clauses
    {
      name: 5,
      description: 3,
      notes: 1
    }.map do |col, weight|
      "(ts_rank(to_tsvector('english', episodes.#{col}), " +
      "plainto_tsquery(#{sanitize(options[:search])})) * #{weight})"
    end
  end

  def extra_order_clauses
    [
      "((date(episodes.published_at) - date '2007-01-01') * 0.0003)",
      "(episodes.comments_count * 0.001)",
      "(CASE episodes.revised WHEN TRUE THEN 0.02 ELSE 0 END)",
    ]
  end

  def per_page
    if options[:per_page]
      options[:per_page].to_i
    else
      case options[:view]
      when "list" then 40
      when "grid" then 24
      else 10
      end
    end
  end

  def page
    options[:page].to_i > 0 ? options[:page].to_i : 1
  end

  def applied_filters
    filters = []
    filters << [options[:search], options.merge(search: nil, page: nil)] if options[:search].present?
    filters << ["#{options[:type].titleize} Episodes", options.merge(type: nil, page: nil)] if options[:type].present?
    filters << [tag.display_name, options.merge(tag_id: nil, page: nil)] if tag
    filters
  end
end