defmodule CouchDB do
  @moduledoc """
  Lightweight CouchDB client builder focused on authentication flows.

  The module exposes helpers to build a pre-configured `Tesla.Client`
  alongside a thin wrapper around `Tesla.request/2` to keep the original
  API surface available.
  """

  alias CouchDB.Environment
  alias Tesla.Middleware

  @type interface :: :base | :backend

  @default_headers [{"user-agent", "couchdb_auth"}]
  @default_adapter {Tesla.Adapter.Hackney, []}

  @doc """
  Build a `Tesla.Client` configured for the requested interface.

  The `interface` can be `:base` (default) or `:backend`. Additional
  credential overrides may be supplied via `overrides`.
  """
  @spec client(interface(), map()) :: Tesla.Client.t()
  def client(interface \\ :base, overrides \\ %{}) do
    url = interface_url(interface)

    overrides = Map.new(overrides)
    admin = Environment.server_admin()

    credentials =
      %{
        username: Map.get(overrides, :username, admin.user),
        password: Map.get(overrides, :password, admin.password),
        url: url
      }
      |> Map.merge(Map.drop(overrides, [:username, :password]))

    middleware =
      [
        {Middleware.BaseUrl, url},
        {Middleware.Headers, @default_headers},
        {Middleware.JSON, engine: Jason}
      ] ++ auth_middleware(Environment.auth_type(), credentials, url)

    Tesla.client(middleware, @default_adapter)
  end

  @doc """
  Executes an HTTP request using either the provided `%Tesla.Client{}` or a
  freshly built one.
  """
  @spec request(atom(), String.t(), keyword()) :: {:ok, Tesla.Env.t()} | {:error, any()}
  def request(method, url, opts \\ []) do
    {client, opts} = pop_client(opts)

    request_opts =
      opts
      |> Keyword.put(:method, method)
      |> Keyword.put(:url, url)

    Tesla.request(client, request_opts)
  end

  for verb <- ~w(delete get head options patch post put trace)a do
    @spec unquote(verb)(String.t(), keyword()) :: {:ok, Tesla.Env.t()} | {:error, any()}
    def unquote(verb)(url, opts \\ []) do
      request(unquote(verb), url, opts)
    end
  end

  defp pop_client(opts) do
    case Keyword.pop(opts, :client) do
      {nil, rest_opts} ->
        {interface, rest_opts} = Keyword.pop(rest_opts, :interface, :base)
        overrides = rest_opts |> Keyword.get(:credentials, %{}) |> Map.new()
        rest_opts = Keyword.drop(rest_opts, [:credentials])
        {client(interface, overrides), rest_opts}

      {client, rest_opts} ->
        {client, rest_opts}
    end
  end

  defp interface_url(:backend), do: Environment.backend_url()
  defp interface_url(_), do: Environment.base_url()

  defp auth_middleware(:admin_party, _opts, _url), do: []

  defp auth_middleware(:basic, opts, _url) do
    [{Tesla.Middleware.CouchDB.BasicAuth, opts}]
  end

  defp auth_middleware(:cookie, opts, url) do
    [{Tesla.Middleware.CouchDB.CookieAuth, Map.put(opts, :url, url)}]
  end

  defp auth_middleware(:oauth, opts, url) do
    credentials =
      Environment.oauth_creds()
      |> Map.merge(%{url: url})
      |> Map.merge(opts)

    [{Tesla.Middleware.CouchDB.OAuth, credentials}]
  end

  defp auth_middleware(_, _opts, _url), do: []
end