defmodule CCXT.WS.Subscription.MethodSubscription do
  @moduledoc """
  Hyperliquid-style subscribe frame.

      %{"method" => "subscribe", "subscription" => %{"type" => "allMids"}}

  The channel list must contain exactly one entry; its value becomes the
  `type` field of the nested subscription object. Config keys:
  `:op_field` (default `"method"`), `:args_field` (default `"subscription"`).

  Hyperliquid is in the `:custom` DEX bucket and is **not wired** in
  `CCXT.WS.Config` today — this module is ported for completeness but not
  exercised end-to-end until the DEX custom track unlocks upstream.
  """

  @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
    method = Map.get(config, :op_field, "method")
    subscription = Map.get(config, :args_field, "subscription")
    type = List.first(channels) || ""

    %{method => action, subscription => %{"type" => type}}
  end
end