Port morse code.

morse/lib/morse.ex

@@ -1,13 +1,67 @@
 defmodule Morse do
+  alias Circuits.GPIO
+
   @moduledoc """
   Functions to control the signal lamp connected with GPIO.
   """
 
+  @relay_pin 17
+  @sleep_short 200
+  @sleep_delay 400
+  @sleep_long 700
+  @sleep_pause 1000
+  @sleep_start 3000
+
+  @on 0
+  @off 1
+
   @doc """
-  Takes a string composed of dots and dashes, and signals them with the
-  signal lamp.
+  Signal the provided symbols using GPIO.
+  Also setup the GPIO.
   """
-  def signal(msg) do
-    IO.puts(msg)
+
+  def signal do
+    case System.get_env("MORSE_MESSAGE") do
+      nil ->
+        # Signal for SOS if the env variable wasn't found :)
+        signal("...---...")
+      message -> signal(message)
+    end
+  end
+
+  def signal(symbols) do
+    {:ok, gpio} = GPIO.open(@relay_pin, :output)
+    GPIO.write(gpio, @off)
+    Process.sleep(@sleep_start)
+    signal_sentence(gpio, String.graphemes(symbols))
+  end
+
+  # Signal a whole sentence of symbols with GPIO.
+  defp signal_sentence(gpio, []) do
+    GPIO.write(gpio, @off)
+    GPIO.close(gpio)
+    :ok
+  end
+
+  defp signal_sentence(gpio, [symbol | rest]) when symbol in [".", "-"] do
+    GPIO.write(gpio, @on)
+    case symbol do
+      "." -> Process.sleep(@sleep_short)
+      "-" -> Process.sleep(@sleep_long)
+    end
+    GPIO.write(gpio, @off)
+
+    Process.sleep(@sleep_delay)
+    signal_sentence(gpio, rest)
+  end
+
+  defp signal_sentence(gpio, [" " | rest]) do
+    Process.sleep(@sleep_pause)
+
+    signal_sentence(gpio, rest)
+  end
+
+  defp signal_sentence(_gpio, [symbol | _rest]) do
+    {:error, "Undefined symbol: " <> symbol}
   end
 end