[PR] Add is_valid_url? function

lib/useful.ex

@@ -214,6 +214,17 @@ defmodule Useful do
     "#{key}: #{value}"
   end
 
+  @doc """
+  `is_valid_url?/1` checks if a string is a valid URL.
+  A valid URL starts with a `scheme` (e.g. `http://` or `https://`),
+  so strings that start with "www" are considered invalid.
+  """
+  def is_valid_url?(string) do
+    [:scheme, :host, :port]
+    |> Enum.map(&Map.get(URI.parse(string), &1))
+    |> Enum.all?()
+  end
+
   # Recap: https://elixir-lang.org/getting-started/basic-types.html#tuples
   defp to_list_of_tuples(map) do
     map

test/useful_test.exs

@@ -330,4 +330,17 @@ defmodule UsefulTest do
       assert Useful.typeof(tuple) == "tuple"
     end
   end
+
+  describe "is_valid_url?/1" do
+    test "are URL valid" do
+      assert Useful.is_valid_url?("http://www.google.com") == true
+      assert Useful.is_valid_url?("http//google.com") == false
+      assert Useful.is_valid_url?("ftp://google.com") == true
+      assert Useful.is_valid_url?("https://google.com/api&url=ok") == true
+      assert Useful.is_valid_url?("http://localhost:3000") == true
+      assert Useful.is_valid_url?("https://localhost") == true
+      assert Useful.is_valid_url?("htt:/google") == false
+      assert Useful.is_valid_url?("www.google.com") == false
+    end
+  end
 end