defmodule Flagsmith.SDK.Client do
  use TypedEctoSchema
  alias Flagsmith.SDK

  @type possible_error :: :environment_key | :base_url
  @type tesla_header_list :: [{String.t(), String.t()}]

  import Ecto.Changeset,
    only: [
      cast: 3,
      apply_action: 2,
      validate_required: 2
    ]

  @default_url "https://api.flagsmith.com/api/v1"
  @auth_header "X-Environment-Key"

  @moduledoc """
  The SDK Client struct module.
  The functions in this module should not be called directly, instead use the
  `Flagsmith.SDK.new/0/1/2` function to build a new client struct.
  """

  @primary_key false

  typed_embedded_schema do
    field(:environment_key, SDK.MaybeFunction)
    field(:base_url, SDK.MaybeFunction, default_value: @default_url)
  end

  @doc """
  Returns the base default url for the API query: #{@default_url}
  """
  @spec default_url() :: String.t()
  def default_url(), do: @default_url

  @doc """
  Returns a new `Flagsmith.SDK.Client.t()` to be used on further `Flagsmith.SDK.API`
  function calls.
  """
  @spec new(SDK.Types.environment_key() | nil, SDK.Types.base_url() | nil) ::
          {:ok, SDK.Client.t()} | {:error, possible_error}
  def new(environment_key, base_url) do
    %__MODULE__{}
    |> cast(%{environment_key: environment_key, base_url: base_url}, [:environment_key, :base_url])
    |> validate_required([:environment_key, :base_url])
    |> apply_action(:insert)
    |> case do
      {:ok, _} = ok ->
        ok

      {:error, changeset} ->
        {:error, extract_first_error(changeset)}
    end
  end

  @doc false
  @spec auth_middleware(environment_key :: String.t()) ::
          {Tesla.Middleware.Headers, tesla_header_list()}
  def auth_middleware(environment_key),
    do: {Tesla.Middleware.Headers, auth_header(environment_key)}

  @doc false
  @spec base_url_middleware(base_url :: String.t()) ::
          {Tesla.Middleware.BaseUrl, String.t()}
  def base_url_middleware(base_url),
    do: {Tesla.Middleware.BaseUrl, base_url}

  @spec auth_header(environment_key :: String.t()) :: tesla_header_list()
  defp auth_header(environment_key), do: [{@auth_header, environment_key}]

  @spec extract_first_error(changeset :: Ecto.Changeset.t()) :: atom()
  defp extract_first_error(%Ecto.Changeset{errors: [{error, _} | _]}), do: error
end