defmodule Mercury.Client do
  @moduledoc """
  Holds configuration for talking to the Mercury Banking API and is passed
  as the first argument to every function in `Mercury.Accounts`,
  `Mercury.Transactions`, and the other resource modules.

  Build one with `new/2`:

      client = Mercury.Client.new("secret-token:mercury_production_...")

  `Mercury.Client` is an immutable struct — it is cheap to build and safe to
  share across processes.
  """

  alias Mercury.Retry

  @enforce_keys [:api_key, :base_url, :timeout, :retry, :req]
  defstruct [
    :api_key,
    :base_url,
    :timeout,
    :retry,
    :req,
    :on_request,
    :on_response
  ]

  @type request_hook :: (method :: atom(), url :: String.t(), request_id :: String.t() -> any())
  @type response_hook ::
          (method :: atom(),
           url :: String.t(),
           request_id :: String.t(),
           status :: pos_integer(),
           duration_ms :: non_neg_integer() ->
             any())

  @type t :: %__MODULE__{
          api_key: String.t(),
          base_url: String.t(),
          timeout: pos_integer(),
          retry: Retry.t(),
          req: Req.Request.t(),
          on_request: request_hook() | nil,
          on_response: response_hook() | nil
        }

  @default_base_url "https://api.mercury.com/api/v1"
  @default_timeout 30_000

  @doc """
  Builds a new `Mercury.Client`.

  `api_key` must include the `"secret-token:"` prefix, e.g.
  `"secret-token:mercury_production_..."`.

  ## Options

    * `:base_url` — override the API base URL. Default: `"#{@default_base_url}"`.
    * `:timeout` — per-request timeout in milliseconds. Default: `#{@default_timeout}`.
    * `:retry` — a `Mercury.Retry` struct. Default: `Mercury.Retry.default/0`.
    * `:on_request` — request hook, see `t:request_hook/0`.
    * `:on_response` — response hook, see `t:response_hook/0`.
    * `:req_options` — extra options merged into the underlying `Req.new/1`
      call (e.g. `:plug` for tests, `:connect_options` for proxies).

  ## Examples

      Mercury.Client.new("secret-token:mercury_production_...")

      Mercury.Client.new("secret-token:mercury_sandbox_...",
        base_url: "https://api-sandbox.mercury.com/api/v1",
        timeout: 10_000
      )
  """
  @spec new(api_key :: String.t(), opts :: keyword()) :: t()
  def new(api_key, opts \\ [])

  def new(api_key, _opts) when not is_binary(api_key) or api_key == "" do
    raise ArgumentError,
          "Mercury.Client.new/2 requires a non-empty api_key string " <>
            "(expected the \"secret-token:...\" prefix)"
  end

  def new(api_key, opts) when is_binary(api_key) and is_list(opts) do
    base_url = Keyword.get(opts, :base_url, @default_base_url)
    timeout = Keyword.get(opts, :timeout, @default_timeout)
    retry = Keyword.get(opts, :retry, Retry.default())
    on_request = Keyword.get(opts, :on_request)
    on_response = Keyword.get(opts, :on_response)
    req_options = Keyword.get(opts, :req_options, [])

    req =
      req_options
      |> Keyword.merge(
        base_url: base_url,
        receive_timeout: timeout,
        retry: false,
        headers: [
          {"authorization", "Bearer " <> api_key},
          {"accept", "application/json"},
          {"x-mercury-sdk", Mercury.sdk_version()}
        ]
      )
      |> Req.new()

    %__MODULE__{
      api_key: api_key,
      base_url: base_url,
      timeout: timeout,
      retry: retry,
      req: req,
      on_request: on_request,
      on_response: on_response
    }
  end
end