defmodule BearCli.Api do
  @moduledoc """
  Bear 伺服器 HTTP 介面（一律使用 `Req`）。

  目前僅實作 PAT 模式所需的 `GET /userinfo`。
  """

  @finch BearCli.Finch

  @doc """
  呼叫 `GET {issuer}/userinfo`（Bearer token）。

  回傳：
    - `{:ok, claims}` — 200，claims 為 JSON map
    - `{:error, :unauthorized, description}` — 401
    - `{:error, :server_error, status}` — 其他非 2xx
    - `{:error, :network, reason}` — 傳輸層錯誤
  """
  def userinfo(issuer, token) do
    url = String.trim_trailing(issuer, "/") <> "/userinfo"

    case Req.get(url,
           headers: [authorization: "Bearer " <> token, accept: "application/json"],
           retry: false,
           finch: [name: @finch]
         ) do
      {:ok, %Req.Response{status: 200, body: body}} ->
        {:ok, decode_body(body)}

      {:ok, %Req.Response{status: 401, body: body}} ->
        {:error, :unauthorized, error_description(body)}

      {:ok, %Req.Response{status: status}} ->
        {:error, :server_error, status}

      {:error, exception} ->
        {:error, :network, Exception.message(exception)}
    end
  end

  defp decode_body(%{} = body), do: body
  defp decode_body(body) when is_binary(body), do: Jason.decode!(body)
  defp decode_body(_), do: %{}

  defp error_description(body) when is_binary(body) do
    case Jason.decode(body) do
      {:ok, %{"error_description" => desc}} when is_binary(desc) -> desc
      {:ok, %{"error" => err}} when is_binary(err) -> err
      _ -> "invalid_token"
    end
  end

  defp error_description(_), do: "invalid_token"
end