Use ExchangeRates.lastest_rates/0 default in sum/2

Return {:error, reason} in exchange rates public
API when the retriever isn't running - instead of
letting the process crash.

CHANGELOG.md

@@ -10,6 +10,8 @@ This is the changelog for Money v5.16.0 released on ______, 2024.  For older cha
 
 * Update to [CLDR 45.0](https://cldr.unicode.org/index/downloads/cldr-45) data.
 
+* Return structured errors for `Money.ExchangeRates.latest_rates/0`, `Money.ExchangeRates.historic_rates/1`, `Money.ExchangeRates.last_updated/0` and `Money.ExchangeRates.latest_rates_available?/0` when the exchange rates retrieval process is not running.
+
 ## Money v5.15.4
 
 This is the changelog for Money v5.15.4 released on February 29th, 2024.  For older changelogs please consult the release tag on [GitHub](https://github.com/kipcole9/money/tags)

lib/money.ex

@@ -1295,10 +1295,10 @@ defmodule Money do
 
   ## Examples
 
-      iex> Money.sum [Money.new(:USD, 100), Money.new(:USD, 200), Money.new(:USD, 50)]
+      iex> Money.sum([Money.new(:USD, 100), Money.new(:USD, 200), Money.new(:USD, 50)])
       {:ok, Money.new(:USD, 350)}
 
-      iex> Money.sum [Money.new(:USD, 100), Money.new(:USD, 200), Money.new(:AUD, 50)]
+      iex> Money.sum([Money.new(:USD, 100), Money.new(:USD, 200), Money.new(:AUD, 50)], %{})
       {:error,
        {Money.ExchangeRateError, "No exchange rate is available for currency :AUD"}}
 
@@ -1308,9 +1308,20 @@ defmodule Money do
 
   """
   @doc since: "5.3.0"
-  @spec sum([t(), ...], ExchangeRates.t()) :: {:ok, t} | {:error, {module(), String.t()}}
+  @spec sum([t(), ...], ExchangeRates.t() | {:ok, ExchangeRates.t()} | {:error, {module(), String.t()}}) ::
+    {:ok, t} | {:error, {module(), String.t()}}
 
-  def sum([%Money{} = first | rest] = money_list, rates \\ %{}) when is_list(money_list) do
+  def sum(money_list, rates \\ Money.ExchangeRates.latest_rates())
+
+  def sum(money_list, {:ok, %{} = rates}) when is_list(money_list) do
+    sum(money_list, rates)
+  end
+
+  def sum(money_list, {:error, reason}) when is_list(money_list) do
+    {:error, reason}
+  end
+
+  def sum([%Money{} = first | rest] = money_list, %{} = rates) when is_list(money_list) do
     %Money{currency: target_currency} = first
 
     Enum.reduce_while(rest, {:ok, first}, fn money, {:ok, acc} ->

lib/money/exchange_rates.ex

@@ -240,9 +240,14 @@ defmodule Money.ExchangeRates do
   """
   @spec latest_rates() :: {:ok, map()} | {:error, {Exception.t(), binary}}
   def latest_rates do
-    case cache().latest_rates() do
-      {:ok, rates} -> {:ok, rates}
-      {:error, _} -> Retriever.latest_rates()
+    try do
+      case cache().latest_rates() do
+        {:ok, rates} -> {:ok, rates}
+        {:error, _} -> Retriever.latest_rates()
+      end
+    catch
+      :exit, {:noproc, {GenServer, :call, [Money.ExchangeRates.Retriever, :config, _timeout]}} ->
+        {:error, no_retriever_running_error()}
     end
   end
 
@@ -268,9 +273,14 @@ defmodule Money.ExchangeRates do
   """
   @spec historic_rates(Date.t()) :: {:ok, map()} | {:error, {Exception.t(), binary}}
   def historic_rates(date) do
-    case cache().historic_rates(date) do
-      {:ok, rates} -> {:ok, rates}
-      {:error, _} -> Retriever.historic_rates(date)
+    try do
+      case cache().historic_rates(date) do
+        {:ok, rates} -> {:ok, rates}
+        {:error, _} -> Retriever.historic_rates(date)
+      end
+    catch
+      :exit, {:noproc, {GenServer, :call, [Money.ExchangeRates.Retriever, :config, _timeout]}} ->
+        {:error, no_retriever_running_error()}
     end
   end
 
@@ -280,9 +290,14 @@ defmodule Money.ExchangeRates do
   """
   @spec latest_rates_available?() :: boolean
   def latest_rates_available? do
-    case cache().latest_rates() do
-      {:ok, _rates} -> true
-      _ -> false
+    try do
+      case cache().latest_rates() do
+        {:ok, _rates} -> true
+        _ -> false
+      end
+    catch
+      :exit, {:noproc, {GenServer, :call, [Money.ExchangeRates.Retriever, :config, _timeout]}} ->
+        false
     end
   end
 
@@ -301,6 +316,15 @@ defmodule Money.ExchangeRates do
   """
   @spec last_updated() :: {:ok, DateTime.t()} | {:error, {Exception.t(), binary}}
   def last_updated do
-    cache().last_updated()
+    try do
+      cache().last_updated()
+    catch
+      :exit, {:noproc, {GenServer, :call, [Money.ExchangeRates.Retriever, :config, _timeout]}} ->
+        {:error, no_retriever_running_error()}
+    end
+  end
+
+  defp no_retriever_running_error do
+    {Money.ExchangeRateError, "Exchange Rates retrieval process is not running"}
   end
 end