Split cli messages to case with invalid usage and help message

lib/cli.ex

@@ -6,9 +6,12 @@ defmodule Onigumo.CLI do
   def main(argv) do
     case OptionParser.parse(
            argv,
-           aliases: [C: :working_dir],
-           strict: [working_dir: :string]
+           aliases: [h: :help, C: :working_dir],
+           strict: [help: :boolean, working_dir: :string]
          ) do
+      {[help: true], [], []} ->
+        help_message()
+
       {parsed_switches, [component], []} ->
         {:ok, module} = Map.fetch(@components, String.to_atom(component))
         working_dir = Keyword.get(parsed_switches, :working_dir, File.cwd!())
@@ -20,6 +23,15 @@ defmodule Onigumo.CLI do
   end
 
   defp usage_message() do
+    IO.puts("""
+    onigumo: invalid usage
+    Usage: onigumo [OPTION]... [COMPONENT]
+
+    Try `onigumo --help' for more options.
+    """)
+  end
+
+  defp help_message() do
     components = Enum.join(Map.keys(@components), ", ")
 
     IO.puts("""
@@ -30,6 +42,7 @@ defmodule Onigumo.CLI do
     COMPONENT\tOnigumo component to run, available: #{components}
 
     OPTIONS:
+    -h, --help\t\tprint this help
     -C, --working-dir <dir>\tChange working dir to <dir> before running
     """)
   end

test/onigumo_cli_test.exs

@@ -13,6 +13,12 @@
     "-c"
   ]
 
+  @invalid_switch_combinations [
+    "--help -C invalid",
+    "-h --invalid",
+    "downloader -h"
+  ]
+
   @working_dir_switches [
     "--working-dir",
     "-C"
@@ -39,6 +45,12 @@
       end
     end
 
+    for switches <- @invalid_switch_combinations do
+      test("run invalid combination of switches #{inspect(switches)} ") do
+        assert usage_message_printed?(fn -> Onigumo.CLI.main([unquote(switches)]) end)
+      end
+    end
+
     @tag :tmp_dir
     test("run CLI with 'downloader' argument passing cwd", %{tmp_dir: tmp_dir}) do
       expect(OnigumoDownloaderMock, :main, fn working_dir -> working_dir end)
@@ -60,9 +72,20 @@
       end
     end
 
+    for switch <- ["-h", "--help"] do
+      test("run CLI with a #{inspect(switch)} switch") do
+        assert help_message_printed?(fn -> Onigumo.CLI.main([unquote(switch)]) end)
+      end
+    end
+
     defp usage_message_printed?(function) do
       output = capture_io(function)
-      String.starts_with?(output, "Usage: onigumo ")
+      String.starts_with?(output, "onigumo: invalid usage")
+    end
+
+    defp help_message_printed?(function) do
+      output = capture_io(function)
+      String.starts_with?(output, "Usage: onigumo [OPTION]... [COMPONENT]")
     end
   end
 end