require_dependency 'guardian'
require_dependency 'topic_query'
require_dependency 'filter_best_posts'
require_dependency 'gaps'

class TopicView

  attr_reader :topic, :posts, :guardian, :filtered_posts, :chunk_size, :print, :message_bus_last_id
  attr_accessor :draft, :draft_key, :draft_sequence, :user_custom_fields, :post_custom_fields, :post_number

  def self.slow_chunk_size
    10
  end

  def self.print_chunk_size
    1000
  end

  def self.chunk_size
    20
  end

  def self.default_post_custom_fields
    @default_post_custom_fields ||= ["action_code_who"]
  end

  def self.post_custom_fields_whitelisters
    @post_custom_fields_whitelisters ||= Set.new
  end

  def self.add_post_custom_fields_whitelister(&block)
    post_custom_fields_whitelisters << block
  end

  def self.whitelisted_post_custom_fields(user)
    wpcf = default_post_custom_fields + post_custom_fields_whitelisters.map { |w| w.call(user) }
    wpcf.flatten.uniq
  end

  def initialize(topic_or_topic_id, user = nil, options = {})
    @topic = find_topic(topic_or_topic_id)
    @user = user
    @guardian = Guardian.new(@user)

    check_and_raise_exceptions

    @message_bus_last_id = MessageBus.last_id("/topic/#{@topic.id}")
    @print = options[:print].present?

    options.each do |key, value|
      self.instance_variable_set("@#{key}".to_sym, value)
    end

    @_post_number = @post_number.dup
    @post_number = [@post_number.to_i, 1].max
    @page = [@page.to_i, 1].max

    @chunk_size =
      case
      when options[:slow_platform] then TopicView.slow_chunk_size
      when @print then TopicView.print_chunk_size
      else TopicView.chunk_size
      end

    @limit ||= @chunk_size

    setup_filtered_posts

    @initial_load = true
    @index_reverse = false

    filter_posts(options)

    if @posts
      if (added_fields = User.whitelisted_user_custom_fields(@guardian)).present?
        @user_custom_fields = User.custom_fields_for_ids(@posts.pluck(:user_id), added_fields)
      end

      if (whitelisted_fields = TopicView.whitelisted_post_custom_fields(@user)).present?
        @post_custom_fields = Post.custom_fields_for_ids(@posts.pluck(:id), whitelisted_fields)
      end
    end

    @draft_key = @topic.draft_key
    @draft_sequence = DraftSequence.current(@user, @draft_key)
  end

  def canonical_path
    path = relative_url
    path <<
      if @page > 1
        "?page=#{@page}"
      else
        page = ((@post_number - 1) / @limit) + 1
        page > 1 ? "?page=#{page}" : ""
      end

    path
  end

  def contains_gaps?
    @contains_gaps
  end

  def gaps
    return unless @contains_gaps

    @gaps ||= begin
      if is_mega_topic?
        nil
      else
        Gaps.new(filtered_post_ids, unfiltered_posts.order(:sort_order).pluck(:id))
      end
    end
  end

  def last_post
    return nil if @posts.blank?
    @last_post ||= @posts.last
  end

  def prev_page
    @page > 1 && posts.size > 0 ? @page - 1 : nil
  end

  def next_page
    @next_page ||= begin
      if last_post && (@topic.highest_post_number > last_post.post_number)
        @page + 1
      end
    end
  end

  def prev_page_path
    if prev_page > 1
      "#{relative_url}?page=#{prev_page}"
    else
      relative_url
    end
  end

  def next_page_path
    "#{relative_url}?page=#{next_page}"
  end

  def absolute_url
    "#{Discourse.base_url}#{relative_url}"
  end

  def relative_url
    "#{@topic.relative_url}#{@print ? '/print' : ''}"
  end

  def page_title
    title = @topic.title
    if SiteSetting.topic_page_title_includes_category
      if @topic.category_id != SiteSetting.uncategorized_category_id && @topic.category_id && @topic.category
        title += " - #{@topic.category.name}"
      elsif SiteSetting.tagging_enabled && @topic.tags.exists?
        title += " - #{@topic.tags.order('tags.topic_count DESC').first.name}"
      end
    end
    title
  end

  def title
    @topic.title
  end

  def desired_post
    return @desired_post if @desired_post.present?
    return nil if posts.blank?

    @desired_post = posts.detect { |p| p.post_number == @post_number }
    @desired_post ||= posts.first
    @desired_post
  end

  def summary(opts = {})
    return nil if desired_post.blank?
    # TODO, this is actually quite slow, should be cached in the post table
    excerpt = desired_post.excerpt(500, opts.merge(strip_links: true, text_entities: true))
    (excerpt || "").gsub(/\n/, ' ').strip
  end

  def read_time
    return nil if @post_number > 1 # only show for topic URLs
    (@topic.word_count / SiteSetting.read_time_word_count).floor if @topic.word_count
  end

  def like_count
    return nil if @post_number > 1 # only show for topic URLs
    @topic.like_count
  end

  def image_url
    if @post_number > 1 && @desired_post.present?
      if @desired_post.image_url.present?
        @desired_post.image_url
      elsif @desired_post.user
        # show poster avatar
        @desired_post.user.avatar_template_url.gsub("{size}", "200")
      end
    else
      @topic.image_url
    end
  end

  def filter_posts(opts = {})
    return filter_posts_near(opts[:post_number].to_i) if opts[:post_number].present?
    return filter_posts_by_ids(opts[:post_ids]) if opts[:post_ids].present?
    return filter_best(opts[:best], opts) if opts[:best].present?

    filter_posts_paged(@page)
  end

  def primary_group_names
    return @group_names if @group_names

    primary_group_ids = Set.new
    @posts.each do |p|
      primary_group_ids << p.user.primary_group_id if p.user.try(:primary_group_id)
    end

    result = {}
    unless primary_group_ids.empty?
      Group.where(id: primary_group_ids.to_a).pluck(:id, :name).each do |g|
        result[g[0]] = g[1]
      end
    end

    @group_names = result
  end

  # Find the sort order for a post in the topic
  def sort_order_for_post_number(post_number)
    posts = Post.where(topic_id: @topic.id, post_number: post_number).with_deleted
    posts = filter_post_types(posts)
    posts.select(:sort_order).first.try(:sort_order)
  end

  # Filter to all posts near a particular post number
  def filter_posts_near(post_number)
    posts_before = (@limit.to_f / 4).floor
    posts_before = 1 if posts_before.zero?

    sort_order_sql = <<~SQL
    (
      SELECT posts.sort_order
      FROM posts
      WHERE posts.post_number = #{post_number.to_i}
      AND posts.topic_id = #{@topic.id.to_i}
      LIMIT 1
    )
    SQL

    before_post_ids = @filtered_posts.order(sort_order: :desc)
      .where("posts.sort_order < #{sort_order_sql}",)
      .limit(posts_before)
      .pluck(:id)

    post_ids = before_post_ids + @filtered_posts.order(sort_order: :asc)
      .where("posts.sort_order >= #{sort_order_sql}")
      .limit(@limit - before_post_ids.length)
      .pluck(:id)

    if post_ids.length < @limit
      post_ids = post_ids + @filtered_posts.order(sort_order: :desc)
        .where("posts.sort_order < #{sort_order_sql}")
        .offset(before_post_ids.length)
        .limit(@limit - post_ids.length)
        .pluck(:id)
    end

    filter_posts_by_ids(post_ids)
  end

  def filter_posts_paged(page)
    page = [page, 1].max
    min = @limit * (page - 1)

    # Sometimes we don't care about the OP, for example when embedding comments
    min = 1 if min == 0 && @exclude_first

    @posts = filter_posts_by_ids(
      @filtered_posts.order(:sort_order)
        .offset(min)
        .limit(@limit)
        .pluck(:id)
    )
  end

  def filter_best(max, opts = {})
    filter = FilterBestPosts.new(@topic, @filtered_posts, max, opts)
    @posts = filter.posts
    @filtered_posts = filter.filtered_posts
  end

  def read?(post_number)
    return true unless @user
    read_posts_set.include?(post_number)
  end

  def has_deleted?
    @predelete_filtered_posts.with_deleted
      .where("posts.deleted_at IS NOT NULL")
      .where("posts.post_number > 1")
      .exists?
  end

  def topic_user
    @topic_user ||= begin
      return nil if @user.blank?
      @topic.topic_users.find_by(user_id: @user.id)
    end
  end

  MAX_PARTICIPANTS = 24

  def post_counts_by_user
    @post_counts_by_user ||= begin
      if is_mega_topic?
        {}
      else
        post_ids = unfiltered_post_ids

        return {} if post_ids.blank?

        sql = <<~SQL
          SELECT user_id, count(*) AS count_all
            FROM posts
           WHERE id in (:post_ids)
             AND user_id IS NOT NULL
        GROUP BY user_id
        ORDER BY count_all DESC
           LIMIT #{MAX_PARTICIPANTS}
        SQL

        Hash[*DB.query_single(sql, post_ids: post_ids)]
      end
    end
  end

  # if a topic has more that N posts no longer attempt to
  # get accurate participant count, instead grab cached count
  # from topic
  MAX_POSTS_COUNT_PARTICIPANTS = 500

  def participant_count
    @participant_count ||=
      begin
        if participants.size == MAX_PARTICIPANTS
          if @topic.posts_count > MAX_POSTS_COUNT_PARTICIPANTS
            @topic.participant_count
          else
            sql = <<~SQL
              SELECT COUNT(DISTINCT user_id)
              FROM posts
              WHERE id IN (:post_ids)
              AND user_id IS NOT NULL
            SQL
            DB.query_single(sql, post_ids: unfiltered_post_ids).first.to_i
          end
        else
          participants.size
        end
      end
  end

  def participants
    @participants ||= begin
      participants = {}
      User.where(id: post_counts_by_user.keys).includes(:primary_group).each { |u| participants[u.id] = u }
      participants
    end
  end

  def all_post_actions
    @all_post_actions ||= PostAction.counts_for(@posts, @user)
  end

  def all_active_flags
    @all_active_flags ||= PostAction.active_flags_counts_for(@posts)
  end

  def links
    @links ||= TopicLink.topic_map(@guardian, @topic.id)
  end

  def link_counts
    @link_counts ||= TopicLink.counts_for(@guardian, @topic, posts)
  end

  # Are we the initial page load? If so, we can return extra information like
  # user post counts, etc.
  def initial_load?
    @initial_load
  end

  def suggested_topics
    @suggested_topics ||= TopicQuery.new(@user).list_suggested_for(topic)
  end

  # This is pending a larger refactor, that allows custom orders
  #  for now we need to look for the highest_post_number in the stream
  #  the cache on topics is not correct if there are deleted posts at
  #  the end of the stream (for mods), nor is it correct for filtered
  #  streams
  def highest_post_number
    @highest_post_number ||= @filtered_posts.maximum(:post_number)
  end

  def recent_posts
    @filtered_posts.by_newest.with_user.first(25)
  end

  # Returns an array of [id, days_ago] tuples.
  # `days_ago` is there for the timeline calculations.
  def filtered_post_stream
    @filtered_post_stream ||= begin
      posts = @filtered_posts
        .order(:sort_order)

      columns = [:id]

      if !is_mega_topic?
        columns << 'EXTRACT(DAYS FROM CURRENT_TIMESTAMP - created_at)::INT AS days_ago'
      end

      posts.pluck(*columns)
    end
  end

  def filtered_post_ids
    @filtered_post_ids ||= filtered_post_stream.map do |tuple|
      if is_mega_topic?
        tuple
      else
        tuple[0]
      end
    end
  end

  def unfiltered_post_ids
    @unfiltered_post_ids ||=
      begin
        if @contains_gaps
          unfiltered_posts.pluck(:id)
        else
          filtered_post_ids
        end
      end
  end

  def filtered_post_id(post_number)
    @filtered_posts.where(post_number: post_number).pluck(:id).first
  end

  protected

  def read_posts_set
    @read_posts_set ||= begin
      result = Set.new
      return result unless @user.present?
      return result unless topic_user.present?

      post_numbers = PostTiming
        .where(topic_id: @topic.id, user_id: @user.id)
        .where(post_number: @posts.pluck(:post_number))
        .pluck(:post_number)

      post_numbers.each { |pn| result << pn }
      result
    end
  end

  private

  def filter_post_types(posts)
    visible_types = Topic.visible_post_types(@user)

    if @user.present?
      posts.where("posts.user_id = ? OR post_type IN (?)", @user.id, visible_types)
    else
      posts.where(post_type: visible_types)
    end
  end

  def filter_posts_by_ids(post_ids)
    # TODO: Sort might be off
    @posts = Post.where(id: post_ids, topic_id: @topic.id)
      .includes({ user: :primary_group }, :reply_to_user, :deleted_by, :incoming_email, :topic)
      .order('sort_order')
    @posts = filter_post_types(@posts)
    @posts = @posts.with_deleted if @guardian.can_see_deleted_posts?
    @posts
  end

  def find_topic(topic_or_topic_id)
    if topic_or_topic_id.is_a?(Topic)
      topic_or_topic_id
    else
      # with_deleted covered in #check_and_raise_exceptions
      finder = Topic.with_deleted.where(id: topic_or_topic_id).includes(:category)
      finder.first
    end
  end

  def unfiltered_posts
    result = filter_post_types(@topic.posts)
    result = result.with_deleted if @guardian.can_see_deleted_posts?
    result = result.where("user_id IS NOT NULL") if @exclude_deleted_users
    result = result.where(hidden: false) if @exclude_hidden
    result
  end

  def setup_filtered_posts
    # Certain filters might leave gaps between posts. If that's true, we can return a gap structure
    @contains_gaps = false
    @filtered_posts = unfiltered_posts

    # Filters
    if @filter == 'summary'
      @filtered_posts = @filtered_posts.summary(@topic.id)
      @contains_gaps = true
    end

    if @best.present?
      @filtered_posts = @filtered_posts.where('posts.post_type = ?', Post.types[:regular])
      @contains_gaps = true
    end

    # Username filters
    if @username_filters.present?
      usernames = @username_filters.map { |u| u.downcase }

      @filtered_posts = @filtered_posts.where('
        posts.post_number = 1
        OR posts.user_id IN (SELECT u.id FROM users u WHERE u.username_lower IN (?))
      ', usernames)

      @contains_gaps = true
    end

    # Deleted
    # This should be last - don't want to tell the admin about deleted posts that clicking the button won't show
    # copy the filter for has_deleted? method
    @predelete_filtered_posts = @filtered_posts.spawn

    if @guardian.can_see_deleted_posts? && !@show_deleted && has_deleted?
      @filtered_posts = @filtered_posts.where(
        "posts.deleted_at IS NULL OR posts.post_number = 1"
      )

      @contains_gaps = true
    end

  end

  def check_and_raise_exceptions
    raise Discourse::NotFound if @topic.blank?
    # Special case: If the topic is private and the user isn't logged in, ask them
    # to log in!
    if @topic.present? && @topic.private_message? && @user.blank?
      raise Discourse::NotLoggedIn.new
    end
    # can user see this topic?
    raise Discourse::InvalidAccess.new("can't see #{@topic}", @topic) unless @guardian.can_see?(@topic)
    # log personal message views
    if SiteSetting.log_personal_messages_views && @topic.present? && @topic.private_message? && @topic.all_allowed_users.where(id: @user.id).blank?
      unless UserHistory.where(acting_user_id: @user.id, action: UserHistory.actions[:check_personal_message], topic_id: @topic.id).where("created_at > ?", 1.hour.ago).exists?
        StaffActionLogger.new(@user).log_check_personal_message(@topic)
      end
    end
  end

  MEGA_TOPIC_POSTS_COUNT = 10000

  def is_mega_topic?
    @is_mega_topic ||= (@topic.posts_count >= MEGA_TOPIC_POSTS_COUNT)
  end
end