add make_unique_keys/1

lib/useful.ex

@@ -286,6 +286,30 @@ defmodule Useful do
     def typeof(x) when unquote(:"is_#{type}")(x), do: unquote(type)
   end
 
+  @doc """
+  `make_unique_keys/1` turns a list of tuples with the same key into a list of tuples with a unique key.
+
+  Useful when you deal with "multipart".
+
+  ## Example
+
+      iex> parts = [{"file", "header", "pic1.png"}, {"file", "header", "pic2.png"}]
+      iex> Useful.make_unique_keys(parts)
+      [{"file-2", "header", "pic2.png"}, {"file-1", "header", "pic1.png"}]
+  """
+
+  def make_unique_keys(parts) do
+    key = parts |> hd() |> elem(0)
+    new_keys = Enum.map(1..length(parts), &(key <> "-#{&1}"))
+
+    Enum.zip_reduce([parts, new_keys], [], fn [elt, new_key], acc ->
+      [
+        elt |> Tuple.delete_at(0) |> Tuple.insert_at(0, new_key)
+        | acc
+      ]
+    end)
+  end
+
   # No idea how to test this. Do you? ¯\_(ツ)_/¯
   # coveralls-ignore-start
   def typeof(_) do

test/useful_test.exs

@@ -3,6 +3,13 @@ defmodule UsefulTest do
   use Plug.Test
   doctest Useful
 
+  test "make_unique_keys/1 makes unique keys" do
+    parts = [{"file", 1, "a"}, {"file", 2, "b"}, {"file", 3, "c"}]
+
+    assert Useful.make_unique_keys(parts) |> Enum.sort() ==
+             [{"file-1", 1, "a"}, {"file-2", 2, "b"}, {"file-3", 3, "c"}]
+  end
+
   test "atomize_map_keys/1 converts string keys to map" do
     map = %{"name" => "alex", id: 1}
     # IO.inspect(map, label: "map")