feat: add timezone handling

test/mv_web/helpers/date_formatter_test.exs

@@ -0,0 +1,63 @@
+defmodule MvWeb.Helpers.DateFormatterTest do
+  @moduledoc """
+  Tests for DateFormatter: date/datetime formatting and timezone conversion for display.
+  """
+  use ExUnit.Case, async: true
+
+  alias MvWeb.Helpers.DateFormatter
+
+  describe "format_date/1" do
+    test "formats Date to European format (dd.mm.yyyy)" do
+      assert DateFormatter.format_date(~D[2024-03-15]) == "15.03.2024"
+    end
+
+    test "returns empty string for nil" do
+      assert DateFormatter.format_date(nil) == ""
+    end
+
+    test "returns 'Invalid date' for non-Date" do
+      assert DateFormatter.format_date("2024-03-15") == "Invalid date"
+    end
+  end
+
+  describe "format_datetime/1 and format_datetime/2" do
+    test "formats UTC DateTime without timezone (European format)" do
+      dt = ~U[2024-03-15 10:30:00Z]
+      assert DateFormatter.format_datetime(dt) == "15.03.2024 10:30"
+    end
+
+    test "format_datetime with nil timezone same as no timezone (UTC)" do
+      dt = ~U[2024-03-15 10:30:00Z]
+      assert DateFormatter.format_datetime(dt, nil) == "15.03.2024 10:30"
+    end
+
+    test "formats DateTime in Europe/Berlin (CET/CEST)" do
+      # Winter: 10:30 UTC = 11:30 CET (UTC+1)
+      dt = ~U[2024-01-15 10:30:00Z]
+      assert DateFormatter.format_datetime(dt, "Europe/Berlin") == "15.01.2024 11:30"
+
+      # Summer: 10:30 UTC = 12:30 CEST (UTC+2)
+      dt_summer = ~U[2024-07-15 10:30:00Z]
+      assert DateFormatter.format_datetime(dt_summer, "Europe/Berlin") == "15.07.2024 12:30"
+    end
+
+    test "empty string timezone falls back to UTC" do
+      dt = ~U[2024-03-15 10:30:00Z]
+      assert DateFormatter.format_datetime(dt, "") == "15.03.2024 10:30"
+    end
+
+    test "invalid timezone falls back to UTC" do
+      dt = ~U[2024-03-15 10:30:00Z]
+      assert DateFormatter.format_datetime(dt, "Invalid/Zone") == "15.03.2024 10:30"
+    end
+
+    test "returns empty string for nil datetime" do
+      assert DateFormatter.format_datetime(nil) == ""
+      assert DateFormatter.format_datetime(nil, "Europe/Berlin") == ""
+    end
+
+    test "returns 'Invalid datetime' for non-DateTime" do
+      assert DateFormatter.format_datetime("2024-03-15 10:30") == "Invalid datetime"
+    end
+  end
+end