defmodule LSG.IRC.LinkPlugin do
  @moduledoc """
  # Link Previewer

  An extensible link previewer for IRC.

  To extend the supported sites, create a new handler implementing the callbacks.

  See `link_plugin/` directory for examples. The first in list handler that returns true to the `match/2` callback will be used,
  and if the handler returns `:error` or crashes, will fallback to the default preview.

  Unsupported websites will use the default link preview method, which is for html document the title, otherwise it'll use
  the mimetype and size.

  ## Configuration:

  ```
  config :lsg, LSG.IRC.LinkPlugin,
    handlers: [
      LSG.IRC.LinkPlugin.Youtube: [
        invidious: true
      ],
      LSG.IRC.LinkPlugin.Twitter: [],
      LSG.IRC.LinkPlugin.Imgur: [],
    ]
  ```

  """

  @ircdoc """
  # Link preview

  Previews links (just post a link!).

  Announces real URL after redirections and provides extended support for YouTube, Twitter and Imgur.
  """
  def short_irc_doc, do: false
  def irc_doc, do: @ircdoc
  require Logger

  def start_link() do
    GenServer.start_link(__MODULE__, [], name: __MODULE__)
  end

  @callback match(uri :: URI.t, options :: Keyword.t) :: {true, params :: Map.t} | false
  @callback expand(uri :: URI.t, params :: Map.t, options :: Keyword.t) :: {:ok, lines :: [] | String.t} | :error
  @callback post_match(uri :: URI.t, content_type :: binary, headers :: [], opts :: Keyword.t) :: {:body | :file, params :: Map.t} | false
  @callback post_expand(uri :: URI.t, body :: binary() | Path.t, params :: Map.t, options :: Keyword.t) :: {:ok, lines :: [] | String.t} | :error

  @optional_callbacks [expand: 3, post_expand: 4]

  defstruct [:client]

  def init([]) do
    {:ok, _} = Registry.register(IRC.PubSub, "messages", [plugin: __MODULE__])
    #{:ok, _} = Registry.register(IRC.PubSub, "messages:telegram", [plugin: __MODULE__])
    Logger.info("Link handler started")
    {:ok, %__MODULE__{}}
  end

  def handle_info({:irc, :text, message = %{text: text}}, state) do
    String.split(text)
    |> Enum.map(fn(word) ->
      if String.starts_with?(word, "http://") || String.starts_with?(word, "https://") do
        uri = URI.parse(word)
        if uri.scheme && uri.host do
          spawn(fn() ->
            :timer.kill_after(:timer.seconds(30))
            case expand_link([uri]) do
              {:ok, uris, text} ->
                text = case uris do
                  [uri] -> text
                  [luri | _] ->
                    if luri.host == uri.host && luri.path == luri.path do
                      text
                    else
                      ["-> #{URI.to_string(luri)}", text]
                    end
                end
                if is_list(text) do
                  for line <- text, do: message.replyfun.(line)
                else
                  message.replyfun.(text)
                end
              _ -> nil
            end
          end)
        end
      end
    end)
    {:noreply, state}
  end

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

  def terminate(_reason, state) do
    :ok
  end

  # 1. Match the first valid handler
  # 2. Try to run the handler
  # 3. If :error or crash, default link.
  #    If :skip, nothing
  # 4. ?

  # Over five redirections: cancel.
  def expand_link(acc = [_, _, _, _, _ | _]) do
    {:ok, acc, "link redirects more than five times"}
  end

  def expand_link(acc=[uri | _]) do
    Logger.debug("link: expanding: #{inspect uri}")
    handlers = Keyword.get(Application.get_env(:lsg, __MODULE__, [handlers: []]), :handlers)
    handler = Enum.reduce_while(handlers, nil, fn({module, opts}, acc) ->
      Logger.debug("link: attempt expanding: #{inspect module} for #{inspect uri}")
      module = Module.concat([module])
      case module.match(uri, opts) do
        {true, params} -> {:halt, {module, params, opts}}
        false -> {:cont, acc}
      end
    end)
    run_expand(acc, handler)
  end

  def run_expand(acc, nil) do
    expand_default(acc)
  end

  def run_expand(acc=[uri|_], {module, params, opts}) do
    Logger.debug("link: expanding #{inspect uri} with #{inspect module}")
    case module.expand(uri, params, opts) do
      {:ok, data} -> {:ok, acc, data}
      :error -> expand_default(acc)
      :skip -> nil
    end
  rescue
    e ->
      Logger.error("link: rescued #{inspect uri} with #{inspect module}: #{inspect e}")
      Logger.error(Exception.format(:error, e, __STACKTRACE__))
      expand_default(acc)
  catch
    e, b ->
      Logger.error("link: catched #{inspect uri} with #{inspect module}: #{inspect {e, b}}")
      expand_default(acc)
  end

  defp get(url, headers \\ [], options \\ []) do
    get_req(url, :hackney.get(url, headers, <<>>, options))
  end

  defp get_req(_, {:error, reason}) do
    {:error, reason}
  end

  defp get_req(url, {:ok, 200, headers, client}) do
    headers = Enum.reduce(headers, %{}, fn({key, value}, acc) ->
      Map.put(acc, String.downcase(key), value)
    end)
    content_type = Map.get(headers, "content-type", "application/octect-stream")
    length = Map.get(headers, "content-length", "0")
    {length, _} = Integer.parse(length)

    handlers = Keyword.get(Application.get_env(:lsg, __MODULE__, [handlers: []]), :handlers)
    handler = Enum.reduce_while(handlers, false, fn({module, opts}, acc) ->
      module = Module.concat([module])
      try do
        case module.post_match(url, content_type, headers, opts) do
          {mode, params} when mode in [:body, :file] -> {:halt, {module, params, opts, mode}}
          false -> {:cont, acc}
        end
      rescue
        e ->
          Logger.error(inspect(e))
          {:cont, false}
      catch
        e, b ->
          Logger.error(inspect({b}))
          {:cont, false}
      end
    end)

    cond do
      handler != false and length <= 30_000_000 ->
        case get_body(url, 30_000_000, client, handler, <<>>) do
          {:ok, _} = ok -> ok
          :error ->
            {:ok, "file: #{content_type}, size: #{human_size(length)}"}
        end
      #String.starts_with?(content_type, "text/html") && length <= 30_000_000 ->
      #  get_body(url, 30_000_000, client, <<>>)
      true ->
        :hackney.close(client)
        {:ok, "file: #{content_type}, size: #{human_size(length)}"}
    end
  end

  defp get_req(_, {:ok, redirect, headers, client}) when redirect in 300..399 do
    headers = Enum.reduce(headers, %{}, fn({key, value}, acc) ->
      Map.put(acc, String.downcase(key), value)
    end)
    location = Map.get(headers, "location")

    :hackney.close(client)
    {:redirect, location}
  end

  defp get_req(_, {:ok, status, headers, client}) do
    :hackney.close(client)
    {:error, status, headers}
  end

  defp get_body(url, len, client, {handler, params, opts, mode} = h, acc) when len >= byte_size(acc) do
    case :hackney.stream_body(client) do
      {:ok, data} ->
        get_body(url, len, client, h, << acc::binary, data::binary >>)
      :done ->
        body = case mode do
          :body -> acc
          :file ->
            {:ok, tmpfile} = Plug.Upload.random_file("linkplugin")
            File.write!(tmpfile, acc)
            tmpfile
        end
        handler.post_expand(url, body, params, opts)
      {:error, reason} ->
        {:ok, "failed to fetch body: #{inspect reason}"}
    end
  end

  defp get_body(_, len, client, h, _acc) do
    :hackney.close(client)
    IO.inspect(h)
    {:ok, "Error: file over 30"}
  end

  def expand_default(acc = [uri = %URI{scheme: scheme} | _]) when scheme in ["http", "https"] do
    Logger.debug("link: expanding #{uri} with default")
    headers = [{"user-agent", "DmzBot (like TwitterBot)"}]
    options = [follow_redirect: false, max_body_length: 30_000_000]
    case get(URI.to_string(uri), headers, options) do
      {:ok, text} ->
        {:ok, acc, text}
      {:redirect, link} ->
        new_uri = URI.parse(link)
        #new_uri = %URI{new_uri | scheme: scheme, authority: uri.authority, host: uri.host, port: uri.port}
        expand_link([new_uri | acc])
      {:error, status, _headers} ->
        text = Plug.Conn.Status.reason_phrase(status)
        {:ok, acc, "Error: HTTP #{text} (#{status})"}
      {:error, {:tls_alert, {:handshake_failure, err}}} ->
        {:ok, acc, "TLS Error: #{to_string(err)}"}
      {:error, reason} ->
        {:ok, acc, "Error: #{to_string(reason)}"}
    end
  end

  # Unsupported scheme, came from a redirect.
  def expand_default(acc = [uri | _]) do
    {:ok, [uri], "-> #{URI.to_string(uri)}"}
  end


  defp human_size(bytes) do
    bytes
    |> FileSize.new(:b)
    |> FileSize.scale()
    |> FileSize.format()
  end
end