1 files changed, 104 insertions, 0 deletions
diff --git a/lib/util/public_suffix.ex b/lib/util/public_suffix.ex
new file mode 100644
index 0000000..e34994a
--- /dev/null
+++ b/lib/util/public_suffix.ex
@@ -0,0 +1,104 @@
+defmodule Lithium.Util.PublicSuffix do
+  use GenServer
+
+  require Logger
+
+  @moduledoc """
+  A GenServer that loads the public suffix list from a file and provides
+  functionality to find the organisational domain of a given domain name.
+  """
+
+  @public_suffix_list_path Application.app_dir(:lithium, "priv/public_suffix_list.dat")
+  @public_suffix_list_url "https://publicsuffix.org/list/public_suffix_list.dat"
+  @public_suffix_max_age :timer.hours(7 * 24)
+
+  def start_link(_) do
+    GenServer.start_link(__MODULE__, :ok, name: __MODULE__)
+  end
+
+  @impl true
+  def init(:ok) do
+    if File.exists?(@public_suffix_list_path) do
+      {:ok, load_public_suffix_list()}
+    else
+      {:ok, []}
+    end
+  end
+
+  @impl true
+  def handle_info(:update_public_suffix_list, state) do
+    case fetch_public_suffix_list() do
+      {:ok, new_list} ->
+        {:noreply, new_list}
+
+      {:error, reason} ->
+        Logger.error("Failed to update public suffix list: #{reason}")
+        {:noreply, state}
+    end
+  end
+
+  @impl true
+  def handle_call({:get_domain, domain}, _from, state) do
+    {:reply, find_organizational_domain(domain, state), state}
+  end
+
+  def load_public_suffix_list do
+    case File.read(@public_suffix_list_path) do
+      {:ok, content} ->
+        content
+        |> String.split("\n", trim: true)
+        |> Enum.reject(&String.starts_with?(&1, "//"))
+        |> Enum.map(&String.trim/1)
+        |> Enum.map(&String.downcase/1)
+        |> Enum.map(&String.replace(&1, "*.", ""))
+
+      {:error, reason} ->
+        Logger.error("Failed to load public suffix list: #{reason}")
+        []
+    end
+  end
+
+  def fetch_public_suffix_list do
+    request = :httpc.request(:get, {@public_suffix_list_url, []}, [], [])
+
+    case request do
+      {:ok, {{_, 200, _}, _, body}} ->
+        File.write(@public_suffix_list_path, body)
+        {:ok, load_public_suffix_list()}
+
+      {:error, reason} ->
+        {:error, reason}
+    end
+  end
+
+  def find_organizational_domain(domain, public_suffix_list) do
+    # x.y.z.jb3.dev -> jb3.dev
+
+    # ["com", "jb3", "example"]
+    domain_parts = String.split(domain, ".") |> Enum.reverse()
+
+    # [["com", "public-suffix"], ...]
+    suffix_parts =
+      Enum.map(public_suffix_list, &String.split(&1, ".")) |> Enum.map(&Enum.reverse/1)
+
+    # Add domain parts together until it is no longer in the suffix_parts list
+
+    Enum.reduce_while(domain_parts, [], fn part, acc ->
+      new_acc = acc ++ [part]
+
+      if Enum.member?(suffix_parts, new_acc) do
+        {:cont, new_acc}
+      else
+        {:halt, new_acc}
+      end
+    end)
+    |> Enum.reverse()
+    |> Enum.join(".")
+    |> String.downcase()
+    |> String.trim()
+  end
+
+  def get_domain(domain) do
+    GenServer.call(__MODULE__, {:get_domain, domain})
+  end
+end