defmodule Meta.LDAP do
  require Logger
  use GenServer

  # Every request to the LDAP backend go through this GenServer.

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

  def init(_) do
    {:ok, connect()}
  end

  def handle_call({:pool, query}, _from, state) do
    case state do
      %{status: :ok, conn: ldap_conn} ->
        result = internal_execute_query(query, ldap_conn)
        if (result == {:error, :ldap_closed}) do
          {:reply, result, connect()}
        else
          {:reply, result, state}
        end
      %{status: :error, conn: nil} ->
        state = connect()
        if (state.status == :ok) do
          result = internal_execute_query(query, state.conn)
          {:reply, result, state}
        else
          error = {:error, "Unable to contact backend"}
          {:reply, error, state}
        end
    end
  end

  def handle_call({:single, query}, _from, state) do
    single_state = connect()
    case single_state do
      %{status: :ok, conn: ldap_conn} ->
        result = internal_execute_query(query, ldap_conn)
        close(ldap_conn)
        {:reply, result, state}
      %{status: :error, conn: nil} ->
        error = {:error, "Unable to contact backend"}
        {:reply, error, state}
    end
  end

  def terminate(reason, state) do
    if (state.status == :ok), do: close(state.conn)
    Logger.info "Terminating LDAP backend: #{inspect(reason)}."
  end

  ###

  def search(ldap_conn, field, value, search_timeout \\ 1000) do
    base_dn = Application.get_env(:meta, :ldap) |> Keyword.get(:base_dn)
    opts = [
      {:base, to_charlist(base_dn)},
      {:scope, :eldap.wholeSubtree()},
      {:filter, :eldap.equalityMatch(to_charlist(field), value)},
      {:timeout, search_timeout}
    ]

    case :eldap.search(ldap_conn, opts) do
      {:ok, {:eldap_search_result, eldap_result, _}} ->
        entries = Enum.map(
          eldap_result,
          fn entry ->
            {:eldap_entry, dn, attrs} = entry
            Enum.reduce(attrs, %{:dn => dn},
              fn pair, acc ->
                {key, value} = pair
                %{List.to_atom(key) => value} |> Map.merge(acc)
              end
            )
          end
        )

        {:ok, entries}
      {:error, err} -> {:error, err}
    end
  end
  def execute(query), do: GenServer.call(__MODULE__, {:pool, query})
  def execute_single(query), do: GenServer.call(__MODULE__, {:single, query})

  ###

  defp internal_execute_query(query, ldap_conn), do: query.(ldap_conn)

  defp bind(ldap_conn) do
    conf = Application.get_env(:meta, :ldap, [])
    dn = conf |> Keyword.get(:bind_dn)
    pw = conf |> Keyword.get(:bind_pw)

    :eldap.simple_bind(ldap_conn, dn, pw)
  end

  # The method is used by the RC.LDAPTestEnvironment module.
  def connect do
    conf = Application.get_env(:meta, :ldap, [])

    host = Keyword.get(conf, :server, "localhost") |> String.to_charlist
    opts = [
      {:port, Keyword.get(conf, :port, 389)},
      {:ssl, Keyword.get(conf, :ssl, false)},
      {:tcpopts, Keyword.get(conf, :tcpopts, [])}
    ]
    case :eldap.open([host], opts) do
      {:ok, ldap_conn} ->
        Logger.info "Successfuly connected to LDAP server."
        case bind(ldap_conn) do
          {:error, err} ->
            Logger.warning("Could not bind to LDAP server: #{inspect(err)}")
          _ -> :noop
        end

        %{status: :ok, conn: ldap_conn}
      {:error, err} ->
        Logger.warning "Failed to connect to LDAP server: #{inspect(err)}. Authentication will not be possible."
        %{status: :error, conn: nil}
    end
  end

  # The method is used by the RC.LDAPTestEnvironment module.
  def close(ldap_conn) do
    ldap_conn |> :eldap.close
    Logger.debug("An LDAP connection was closed.")
  end
end