defmodule Meta.Odoo do
  use GenServer
  require Logger

  @common_endpoint "/xmlrpc/2/common"
  @object_endpoint "/xmlrpc/2/object"

  # Odoo 14.0 API is documented at https://www.odoo.com/documentation/14.0/webservices/odoo.html

  defp get_odoo_config(key) do
    Application.get_env(:meta, :odoo, [])  |> Keyword.get(key)
  end

  defp post!(call, endpoint) do
    url = get_odoo_config(:server) <> endpoint
    opts = [proxy_auth: {get_odoo_config(:user), get_odoo_config(:secret)}]
    headers = []
    body = call |> XMLRPC.encode!

    response = HTTPoison.post!(url, body, headers, opts).body |> XMLRPC.decode!
    case response do
      %{fault_code: _, fault_string: err} -> {:error, err}
      %{param: result} -> {:ok, result}
    end
  end

  defp authenticate do
    auth_params = [
      get_odoo_config(:database),
      get_odoo_config(:user),
      get_odoo_config(:secret),
      nil
    ]

    try do
      auth_response = %XMLRPC.MethodCall{method_name: "authenticate", params: auth_params}
                      |> post!(@common_endpoint)
      case auth_response do
        {:ok, false} -> {:error, "Could not authenticate against Odoo."}
        {:ok, uid} -> {:ok, uid}
        {:error, err} -> {:error, err}
      end
      rescue e -> {:error, e}
    end
  end

  defp check_odoo_config(key) do
    case get_odoo_config(key) do
      nil ->
        Logger.warn("Odoo #{key} configuration is missing.")
        false
      _value -> true
    end
  end

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

  def init(:ok) do
    # Make sure Odoo configuration is defined.
    conf_ok? = for key <- [:server, :database, :user, :secret], reduce: true do
      acc -> acc && check_odoo_config(key)
    end

    if conf_ok? do
      case authenticate() do
        {:ok, uid} ->
        # Print Odoo version on console (not quite useful...).
          version_call = %XMLRPC.MethodCall{method_name: "version", params: []} |> post!(@common_endpoint)
          {:ok, %{"server_version" => version}} = version_call
          Logger.info("Successfuly authenticated against Odoo #{version} at #{get_odoo_config(:server)}")

          {:ok, uid}
        {:error, err} ->
          Logger.warning("Failed to authenticate against Odoo: #{inspect(err)}")

          # We do not fail here since we do not want to hinder the application's
          # main supervisor if Odoo is down.
          {:ok, nil}
      end
    else
        Logger.warning("Failed to authenticate against Odoo: missing configuration!")

        {:ok, nil}
    end
  end

  def handle_call({method, params}, _from, uid) do
    case uid do
      # uid is nil if start_link's init/1 call failed.
      # ... we try to authenticate once again!
      nil ->
        case init(:ok) do
          {:ok, new_uid} -> handle_call({method, params}, nil, new_uid)
          err -> {:reply, err, nil}
        end
      _ ->
        call = %XMLRPC.MethodCall{
          method_name: method,
          params: [get_odoo_config(:database), uid, get_odoo_config(:secret) | params]
        }
        result = call |> post!(@object_endpoint)

        {:reply, result, uid}
    end
  end

  def query(params), do: execute_kw(params)
  defp execute_kw(params) do
    GenServer.call(__MODULE__, {"execute_kw", params})
  end
end