Allow to set mailgun config from env

lib/bamboo/adapters/mailgun_adapter.ex

@@ -10,8 +10,8 @@ defmodule Bamboo.MailgunAdapter do
       # In config/config.exs, or config.prod.exs, etc.
       config :my_app, MyApp.Mailer,
         adapter: Bamboo.MailgunAdapter,
-        api_key: "my_api_key",
-        domain: "your.domain"
+        api_key: "my_api_key" # or {:system, "MAILGUN_API_KEY"},
+        domain: "your.domain" # or {:system, "MAILGUN_DOMAIN"}
 
       # Define a Mailer. Maybe in lib/my_app/mailer.ex
       defmodule MyApp.Mailer do
@@ -28,13 +28,27 @@ defmodule Bamboo.MailgunAdapter do
 
   @doc false
   def handle_config(config) do
-    for setting <- [:api_key, :domain] do
-      if config[setting] in [nil, ""] do
-        raise_missing_setting_error(config, setting)
-      end
+    config
+    |> Map.put(:api_key, get_setting(config, :api_key))
+    |> Map.put(:domain, get_setting(config, :domain))
+  end
+
+  defp get_setting(config, key) do
+    config[key]
+    |> case do
+      {:system, var} ->
+        System.get_env(var)
+
+      value ->
+        value
     end
+    |> case do
+      value when value in [nil, ""] ->
+        raise_missing_setting_error(config, key)
 
-    config
+      value ->
+        value
+    end
   end
 
   defp raise_missing_setting_error(config, setting) do
@@ -49,6 +63,7 @@ defmodule Bamboo.MailgunAdapter do
 
   def deliver(email, config) do
     body = to_mailgun_body(email)
+    config = handle_config(config)
 
     case :hackney.post(full_uri(config), headers(email, config), body, [:with_body]) do
       {:ok, status, _headers, response} when status > 299 ->

test/lib/bamboo/adapters/mailgun_adapter_test.exs

@@ -4,6 +4,8 @@ defmodule Bamboo.MailgunAdapterTest do
   alias Bamboo.MailgunAdapter
 
   @config %{adapter: MailgunAdapter, api_key: "dummyapikey", domain: "test.tt"}
+  @config_with_env_var_key %{adapter: MailgunAdapter,
+    api_key: {:system, "MAILGUN_API_KEY"}, domain: {:system, "MAILGUN_DOMAIN"}}
 
   defmodule FakeMailgun do
     use Plug.Router
@@ -62,6 +64,19 @@ defmodule Bamboo.MailgunAdapterTest do
     :ok
   end
 
+  test "can read the settings from an ENV var" do
+    System.put_env("MAILGUN_API_KEY", "env_api_key")
+    System.put_env("MAILGUN_DOMAIN", "env_domain")
+
+    config = MailgunAdapter.handle_config(@config_with_env_var_key)
+
+    assert config[:api_key] == "env_api_key"
+    assert config[:domain] == "env_domain"
+
+    System.delete_env("MAILGUN_API_KEY")
+    System.delete_env("MAILGUN_DOMAIN")
+  end
+
   test "raises if the api key is nil" do
     assert_raise ArgumentError, ~r/no api_key set/, fn ->
       MailgunAdapter.handle_config(%{domain: "test.tt"})
@@ -74,6 +89,35 @@ defmodule Bamboo.MailgunAdapterTest do
     end
   end
 
+  test "raises if an invalid ENV var is used for the api_key" do
+    System.put_env("MAILGUN_DOMAIN", "env_domain")
+
+    assert_raise ArgumentError, ~r/no api_key set/, fn ->
+      new_email(from: "foo@bar.com") |> MailgunAdapter.deliver(@config_with_env_var_key)
+    end
+
+    assert_raise ArgumentError, ~r/no api_key set/, fn ->
+      MailgunAdapter.handle_config(@config_with_env_var_key)
+
+    end
+    System.delete_env("MAILGUN_DOMAIN")
+  end
+
+
+  test "raises if an invalid ENV var is used for the domain" do
+    System.put_env("MAILGUN_API_KEY", "env_api_key")
+
+    assert_raise ArgumentError, ~r/no domain set/, fn ->
+      new_email(from: "foo@bar.com") |> MailgunAdapter.deliver(@config_with_env_var_key)
+    end
+
+    assert_raise ArgumentError, ~r/no domain set/, fn ->
+      MailgunAdapter.handle_config(@config_with_env_var_key)
+
+    end
+    System.delete_env("MAILGUN_API_KEY")
+  end
+
   test "deliver/2 sends the to the right url" do
     new_email() |> MailgunAdapter.deliver(@config)