defmodule CCXT.WS.Subscription.MethodAsTopic do
  @moduledoc """
  Coinex/Phemex-style subscribe frame where the method name IS the channel.

      %{"method" => "ticker.subscribe", "params" => [], "id" => 1}

  Callers pass full method names like `["ticker.subscribe"]` in the
  channel list. Only the first entry is used — callers that need multiple
  subscriptions call `subscribe/2` once per channel. `unsubscribe/2`
  converts `.subscribe` suffixes to `.unsubscribe`.

  Config keys: `:op_field` (default `"method"`), `:args_field`
  (default `"params"`).

  Not wired in `CCXT.WS.Config` today (no priority-tier exchange uses it).
  """

  @behaviour CCXT.WS.Subscription.Behaviour

  @impl true
  def subscribe(channels, config) when is_list(channels) do
    method = List.first(channels) || "subscribe"
    build(method, config)
  end

  @impl true
  def unsubscribe(channels, config) when is_list(channels) do
    method =
      channels
      |> List.first()
      |> to_string()
      |> String.replace(".subscribe", ".unsubscribe")

    build(method, config)
  end

  defp build(method_value, config) do
    method_field = Map.get(config, :op_field, "method")
    params_field = Map.get(config, :args_field, "params")

    %{
      method_field => method_value,
      params_field => [],
      "id" => System.unique_integer([:positive, :monotonic])
    }
  end
end