ex_paymob

defmodule ExPaymob.Config do
  @moduledoc """
  Layered configuration resolution for ExPaymob.

  Resolution chain (first match wins):
  1. Per-request opts (e.g., `secret_key: "sk_..."`)
  2. Application env (`config :ex_paymob, secret_key: "sk_..."`)
  3. System env (`PAYMOB_SECRET_KEY`)
  """

  @base_urls %{
    egypt: "https://accept.paymob.com",
    uae: "https://uae.paymob.com",
    ksa: "https://ksa.paymob.com",
    oman: "https://oman.paymob.com"
  }

  @env_mapping %{
    secret_key: "PAYMOB_SECRET_KEY",
    public_key: "PAYMOB_PUBLIC_KEY",
    hmac_secret: "PAYMOB_HMAC_SECRET",
    base_url: "PAYMOB_BASE_URL",
    region: "PAYMOB_REGION"
  }

  @type region :: :egypt | :uae | :ksa | :oman

  @doc """
  Resolves a configuration key using the layered resolution chain.
  """
  @spec resolve(atom(), keyword()) :: term()
  def resolve(key, opts \\ []) do
    from_opts(key, opts) || from_app_env(key) || from_system_env(key) || default(key)
  end

  @doc """
  Resolves the base URL from config, falling back to region-based URL.
  """
  @spec resolve_base_url(keyword()) :: String.t()
  def resolve_base_url(opts \\ []) do
    case resolve(:base_url, opts) do
      nil ->
        region = resolve(:region, opts) || :egypt
        region = if is_binary(region), do: String.to_existing_atom(region), else: region
        Map.fetch!(@base_urls, region)

      url ->
        url
    end
  end

  @doc """
  Returns the configured HTTP client module.
  """
  @spec resolve_http_client(keyword()) :: module()
  def resolve_http_client(opts \\ []) do
    resolve(:http_client, opts) || ExPaymob.Client.ReqAdapter
  end

  @doc """
  Returns the configured JSON library.
  """
  @spec resolve_json_library(keyword()) :: module()
  def resolve_json_library(opts \\ []) do
    resolve(:json_library, opts) || Jason
  end

  @doc """
  Returns the base URL for a given region.
  """
  @spec base_url_for_region(region()) :: String.t()
  def base_url_for_region(region) do
    Map.fetch!(@base_urls, region)
  end

  defp from_opts(key, opts), do: Keyword.get(opts, key)

  defp from_app_env(key), do: Application.get_env(:ex_paymob, key)

  defp from_system_env(key) do
    case Map.get(@env_mapping, key) do
      nil -> nil
      env_var -> System.get_env(env_var)
    end
  end

  defp default(:region), do: :egypt
  defp default(_), do: nil
end