defmodule Frenzy.UpdateFeeds do
  use GenServer
  alias Frenzy.{Repo, Feed, Item, FilterEngine}
  import Ecto.Query
  require Logger

  def start_link(state) do
    GenServer.start_link(__MODULE__, :ok, state)
  end

  def refresh(pid, feed) do
    GenServer.call(pid, {:refresh, feed})
  end

  def init(state) do
    update_feeds()
    schedule_update()
    {:ok, state}
  end

  def handle_call({:refresh, feed}, _from, state) do
    update_feed(feed)
    new_feed = Feed |> Repo.get(feed.id) |> Repo.preload(:items)
    {:reply, new_feed, state}
  end

  def handle_info(:update_feeds, state) do
    update_feeds()
    schedule_update()
    {:noreply, state}
  end

  defp schedule_update() do
    # 15 minutes
    Process.send_after(self(), :update_feeds, 15 * 60 * 1000)
    # 1 minutes
    # Process.send_after(self(), :update_feeds, 60 * 1000)
  end

  defp update_feeds() do
    Logger.info("Updating all feeds")

    Repo.all(from Feed, preload: [:filter])
    |> Enum.map(&update_feed/1)

    prune_old_items()
  end

  defp prune_old_items() do
    {count, _} =
      from(i in Item,
        where: i.read and not i.tombstone,
        # where: i.read_date <= from_now(-1, "week"),
        where: i.read_date <= from_now(-1, "minute"),
        update: [
          set: [tombstone: true, content: nil, creator: nil, date: nil, url: nil, title: nil]
        ]
      )
      |> Repo.update_all([])

    Logger.info("Converted #{count} read items to tombstones")
  end

  defp update_feed(feed) do
    Logger.debug("Updating #{feed.feed_url}")

    case HTTPoison.get(feed.feed_url) do
      {:ok, %HTTPoison.Response{status_code: 200, body: body}} ->
        case Fiet.parse(body) do
          {:ok, rss} ->
            update_feed_from_rss(feed, rss)
        end

      {:ok, %HTTPoison.Response{status_code: 404}} ->
        Logger.warn("RSS feed #{feed.feed_url} not found")

      {:ok, %HTTPoison.Response{status_code: status_code, headers: headers}}
      when status_code in [301, 302] ->
        {"Location", new_url} =
          Enum.find(headers, fn {name, _value} ->
            name == "Location"
          end)

        Logger.debug("Got 301 redirect from #{feed.feed_url} to #{new_url}, updating feed URL")
        changeset = Feed.changeset(feed, %{feed_url: new_url})
        {:ok, feed} = Repo.insert(changeset)
        update_feed(feed)

      {:error, %HTTPoison.Error{reason: reason}} ->
        Logger.error("Couldn't load RSS feed: #{reason}")
    end
  end

  defp update_feed_from_rss(feed, rss) do
    last_updated =
      if rss.updated_at do
        parse_date(rss.updated_at)
      else
        DateTime.utc_now()
      end

    changeset =
      Feed.changeset(feed, %{
        title: rss.title,
        site_url: rss.link.href,
        last_updated: last_updated
      })

    Repo.update(changeset)

    feed = Repo.preload(feed, items: [], filter: [:rules])

    Enum.map(rss.items, fn entry ->
      # todo: use Repo.exists for this
      if !Enum.any?(feed.items, fn item -> item.guid == entry.id end) do
        create_item(feed, entry)
      end
    end)
  end

  defp create_item(feed, entry) do
    url = get_real_url(entry)

    Logger.debug("Creating item for #{url}")

    content =
      case get_article_content(url) do
        {:ok, content} ->
          content

        {:err, reason} ->
          Logger.warn("Unable to fetch article for #{url}: #{reason}")
          entry.description
      end

    item_params = %{
      guid: entry.id,
      title: entry.title,
      url: url,
      date: parse_date(entry.published_at),
      creator: "",
      content: content
    }

    result =
      if feed.filter_enabled do
        case {feed.filter.mode, FilterEngine.matches?(item_params, feed.filter)} do
          {"accept", true} ->
            :store

          {"reject", false} ->
            :store

          _ ->
            Logger.debug("Skipping item #{url} due to feed filter")
            :tombstone
        end
      else
        :store
      end

    changeset =
      case result do
        :store ->
          Ecto.build_assoc(feed, :items, item_params)

        :tombstone ->
          Ecto.build_assoc(feed, :items, %{
            guid: entry.id,
            tombstone: true
          })
      end

    Repo.insert(changeset)
  end

  defp parse_date(str) do
    case Timex.parse(str, "{RFC1123}") do
      {:ok, date} ->
        Timex.Timezone.convert(date, :utc)

      _ ->
        {:ok, date, _} = DateTime.from_iso8601(str)
        Timex.Timezone.convert(date, :utc)
    end
  end

  defp get_real_url(entry) do
    links = Enum.reject(entry.links, fn l -> l.rel == "shorturl" end)

    case Enum.find(links, fn l -> l.rel == "related" end) do
      nil ->
        case Enum.find(links, fn l -> l.rel == "alternate" end) do
          nil -> Enum.fetch!(links, 0).href
          link -> link.href
        end

      link ->
        link.href
    end
  end

  defp get_article_content(url) do
    Logger.debug("Getting article from #{url}")

    case HTTPoison.get(url) do
      {:ok, %HTTPoison.Response{status_code: 200, body: body}} ->
        article = Readability.article(body)
        {:ok, Readability.readable_html(article)}

      {:ok, %HTTPoison.Response{status_code: 404}} ->
        {:err, "404 not found"}

      {:ok, %HTTPoison.Response{status_code: status_code, headers: headers}}
      when status_code in [301, 302] ->
        {"Location", new_url} =
          Enum.find(headers, fn {name, _value} ->
            name == "Location"
          end)

        Logger.debug("Got 301 redirect from #{url} to #{new_url}")
        get_article_content(new_url)

      {:ok, %HTTPoison.Response{status_code: 403}} ->
        {:err, "403 Forbidden"}

      {:error, %HTTPoison.Error{reason: reason}} ->
        {:err, reason}
    end
  end
end