defmodule CCXT.WS.Subscription.ActionSubscribe do
  @moduledoc """
  Alpaca/LBank-style subscribe frame keyed on an `"action"` field with a
  params object.

      %{"action" => "subscribe", "params" => %{"channels" => ["ticker"]}}

  Config keys:
  - `:op_field` — default `"action"`
  - `:args_field` — default `"params"`
  - `:channels_key` — key under which the channel list is placed within
    the params object (default `"channels"`)

  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
    build(channels, config, "subscribe")
  end

  @impl true
  def unsubscribe(channels, config) when is_list(channels) do
    build(channels, config, "unsubscribe")
  end

  defp build(channels, config, action) do
    action_field = Map.get(config, :op_field, "action")
    params_field = Map.get(config, :args_field, "params")
    channels_key = Map.get(config, :channels_key, "channels")

    %{action_field => action, params_field => %{channels_key => channels}}
  end
end