Expose the response mappers

[sitch]

Currently Plaid.Utils.map_body/2 is privately defined, but this can be useful externally to libs. For instance, implementing an Ecto.Type behaviour.

This parsing functionality could be safely moved into its own module and called from Plaid.Utils.handle_resp/2 to maintain the existing public signature.

Moving this to somewhere like Plaid.Middlewares.ResponseHandler makes a lot of sense to me.

[wfgilman]

How would you imagine an external lib using the response mapper?

[sitch]

This is not my exact usecase but it demonstrates a usecase

defmodule MyApp.EctoPlaidTransactions do
  @behaviour Ecto.Type
  
  def type, do: :map

  def cast(%Plaid.Transactions{} = plaid_transactions) do
    {:ok, plaid_transactions}
  end

  def cast(plaid_transactions) when is_map(plaid_transactions) do
    # This is a bit hacky due to an unnecessary transform
    with {:ok, plaid_transactions_binary} <- dump(plaid_transactions) do
      cast(plaid_transactions_binary)
    else
      _ -> :error
    end
  end

  def cast(plaid_transactions) when is_binary(plaid_transactions) do
    # Currently `.map_body/2` is private though
    Plaid.Utils.map_body(plaid_transactions, :transactions)
  end

  def dump(%Plaid.Transactions{} = plaid_transactions) do
    Poison.encode(plaid_transactions)
  end
end

[wfgilman]

Gotcha. Yeah I can do that.

[wfgilman]

@sitch would this PR address your issue?

[sitch]

Yes sir! Very thanks 👍