Add basic metadata to opengraph preview

Also refactor datetime & address utils

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

lib/service/date_time/date_time.ex

@@ -0,0 +1,41 @@
+defmodule Mobilizon.Service.DateTime do
+  @moduledoc """
+  Module to represent a datetime in a given locale
+  """
+  alias Cldr.DateTime.Relative
+
+  def datetime_to_string(%DateTime{} = datetime, locale \\ "en", format \\ :medium) do
+    Mobilizon.Cldr.DateTime.to_string!(datetime, format: format, locale: locale_or_default(locale))
+  end
+
+  def datetime_to_time_string(%DateTime{} = datetime, locale \\ "en", format \\ :short) do
+    Mobilizon.Cldr.Time.to_string!(datetime, format: format, locale: locale_or_default(locale))
+  end
+
+  @spec datetime_tz_convert(DateTime.t(), String.t()) :: DateTime.t()
+  def datetime_tz_convert(%DateTime{} = datetime, timezone) do
+    case DateTime.shift_zone(datetime, timezone) do
+      {:ok, datetime_with_user_tz} ->
+        datetime_with_user_tz
+
+      _ ->
+        datetime
+    end
+  end
+
+  @spec datetime_relative(DateTime.t(), String.t()) :: String.t()
+  def datetime_relative(%DateTime{} = datetime, locale \\ "en") do
+    Relative.to_string!(datetime, Mobilizon.Cldr,
+      relative_to: DateTime.utc_now(),
+      locale: locale_or_default(locale)
+    )
+  end
+
+  defp locale_or_default(locale) do
+    if Mobilizon.Cldr.known_locale_name(locale) do
+      locale
+    else
+      "en"
+    end
+  end
+end