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