defmodule TimeLog.TimePlug do
  import Plug.Conn
  require Logger
  @moduledoc ~S"""
  This plug stops the time a request takes. Also, this module delivers additional useful functionality
  The plug needs to be called as early in the `endpoint.ex` as possible, ideally right after the socked received a request.
  Additionally the get_duration function can be called from everywhere in order to know how long the request took so far.
  Allows calls to get_ip from other apps too.
  """

  @doc false
  def init(_opts) do
    {}
  end

  @doc "Call to TimePlug that initiates the duration measurement and schedules Response logging to take place before sending the response."
  @spec call(Plug.Conn, Map)::Plug.Conn
  def call(conn, _opts) do
    start_time = Time.utc_now
    conn
    |> put_private(:time_plug_start_time, start_time)
  end

  @doc ~S"""
  Log the response including the IP address, correlation_id and headers.
  """
  @spec log_response(Plug.Conn)::Plug.Conn
  def log_response(conn) do
    [c_id] = get_resp_header conn, "correlation_id"
    Logger.info Poison.encode!(%{correlation_id: c_id, type: "Response", http: create_http_map conn}), application_log: 1
    conn
  end

  defp create_http_map(conn) do
    if :controller_body in Map.keys(conn.private) do
        %{method: conn.method, url: conn.request_path, query: conn.query_string, header: inspect(conn.resp_headers),
          ip_address: get_ip(conn), body: Poison.encode!(conn.private[:controller_body]),
          status_code: conn.status, duration_ms: get_duration(conn)}
    else
        %{method: conn.method, url: conn.request_path, query: conn.query_string, header: inspect(conn.resp_headers),
          ip_address: get_ip(conn), body: "There was no body for this request",
          status_code: conn.status, duration_ms: get_duration(conn)}
    end
  end

  @doc ~S"""
  Returns the time in ms the request took so far.
  May be called with either a Time struct `Time` or with the current conn `Plug.Conn`.

  ## Examples
  ```
  iex> TimeLog.TimePlug.get_duration(conn) # Request the duration with a `Plug.Conn` struct
  65

  iex> start_time = Time.utc_now
  ...
  ...
  iex> TimeLog.TimePlug.get_duration(start_time) # Request the duration with a `Time` struct
  65
  ```
  """
  @spec get_duration(Time)::Integer
  def get_duration(start_time = %Time{}) do
    Time.utc_now
    |> Time.diff(start_time, :milliseconds)
    |> round
  end
  @spec get_duration(Plug.Conn)::Time
  def get_duration(conn = %Plug.Conn{}) do
    Time.utc_now
    |> Time.diff(conn.private[:time_plug_start_time], :milliseconds)
    |> round
  end

  @doc ~S"""
  Returns the IP address in a Format fit for logging.
  If set in config the IP addresses retourned are anonymized by replacing the last digits with 'XXX'.
  Requests that use internal (e.g. company) Ip addresses can be filtered if set in config(`config :time_log, internal_ips: ["127.0.0.1"]`).
  """
  @spec get_ip(Plug.Conn)::String
  def get_ip(conn) do
    header_map = conn.req_headers |> Enum.into(%{})
    ip = if is_nil(header_map["x-forwarded-for"]), do: conn.remote_ip |> Tuple.to_list |> Enum.join(".") , else: header_map["x-forwarded-for"]
    |> String.split(",")
    |> List.first
    Logger.debug "IP: #{ip}"
    cond do
      ip in Application.get_env(:time_log, :internal_ips) -> Application.get_env :time_log, :internal_name
      Application.get_env(:time_log, :anonymize_ips?) -> String.replace ip, ~r/\.\d{1,3}$/, ".XXX"
      true -> ip
    end
  end

  @doc ~S"""
  Sets the body to be logged in the conn in the private part for the key `:controller_body`.
  The body will be included in the response logs if present.

  ## Example
  In a REST Api function that is called to send the result JSON. The output paramter may be any `Map` or `Struct`.

  ```
  defp send_response(conn, output) do
    conn
    |> TimeLog.TimePlug.set_controller_body(output)
    |> json(output)
  end
  ```
  """
  @spec set_controller_body(Plug.Conn, Map)::Plug.Conn
  def set_controller_body(conn, body) do
    conn
    |> put_private(:controller_body, body)
  end
end

# -----------------------------------------------------------------------

defmodule TimeLog.PreLogPlug do
  import Plug.Conn
  require Logger
  alias TimeLog.TimePlug
  @moduledoc ~S"""
  This plug logs the incoming requests.
  It logs the IP address and has the ability to anonymize the IP address if set in config.
  """

  @doc false
  def init(_opts) do
    {}
  end
  @doc "Call to PreLogPlug that initiates the request logging."
  @spec call(Plug.Conn, Map)::Plug.Conn
  def call(conn, _opts) do
    unless conn.request_path in Application.get_env(:time_log, :ignore_urls) do
      initiate_logging conn
    else
      conn
    end
  end

  @doc ~S"""
  Initiates Response logging and logs the incoming request.
  Ensures that responses are only logged if the corresponding request was logged as well.
  """
  @spec initiate_logging(Plug.Conn)::Plug.Conn
  def initiate_logging(conn) do
    [c_id] = if is_nil(get_resp_header(conn, "correlation_id")), do: get_resp_header(conn, "x-request-id"), else: get_resp_header(conn, "correlation_id")
    http_map = %{method: conn.method, url: conn.request_path, query: conn.query_string, ip_address: TimePlug.get_ip(conn), header: inspect(conn.req_headers), params: Poison.encode!(conn.params)}
    Logger.info Poison.encode!(%{correlation_id: c_id, type: "Request", http: http_map}), application_log: 1
    Plug.Conn.register_before_send conn, &TimePlug.log_response(&1)
  end
end