feat: add timezone handling

lib/mv_web/helpers/date_formatter.ex

@@ -2,6 +2,7 @@ defmodule MvWeb.Helpers.DateFormatter do
   @moduledoc """
   Centralized date formatting helper for the application.
   Formats dates in European format (dd.mm.yyyy).
+  DateTime can be shown in UTC or in a given IANA timezone (e.g. from browser).
   """
 
   use Gettext, backend: MvWeb.Gettext
@@ -28,19 +29,40 @@ defmodule MvWeb.Helpers.DateFormatter do
   @doc """
   Formats a DateTime struct to European format (dd.mm.yyyy HH:MM).
 
+  When `timezone` is a valid IANA timezone string (e.g. from the browser),
+  the datetime is converted to that zone before formatting. When `timezone` is
+  nil or invalid, the datetime is formatted in UTC.
+
   ## Examples
 
       iex> MvWeb.Helpers.DateFormatter.format_datetime(~U[2024-03-15 10:30:00Z])
       "15.03.2024 10:30"
 
+      iex> MvWeb.Helpers.DateFormatter.format_datetime(~U[2024-03-15 10:30:00Z], "Europe/Berlin")
+      "15.03.2024 11:30"
+
       iex> MvWeb.Helpers.DateFormatter.format_datetime(nil)
       ""
   """
-  def format_datetime(%DateTime{} = dt) do
-    Calendar.strftime(dt, "%d.%m.%Y %H:%M")
+  def format_datetime(%DateTime{} = dt), do: format_datetime(dt, nil)
+  def format_datetime(nil), do: ""
+  def format_datetime(_), do: "Invalid datetime"
+
+  def format_datetime(%DateTime{} = dt, nil), do: format_datetime_utc(dt)
+  def format_datetime(%DateTime{} = dt, ""), do: format_datetime_utc(dt)
+
+  def format_datetime(%DateTime{} = dt, tz) when is_binary(tz) do
+    case DateTime.shift_zone(dt, tz, Tz.TimeZoneDatabase) do
+      {:ok, shifted} -> Calendar.strftime(shifted, "%d.%m.%Y %H:%M")
+      {:error, _} -> format_datetime_utc(dt)
+    end
   end
 
-  def format_datetime(nil), do: ""
+  def format_datetime(nil, _timezone), do: ""
 
-  def format_datetime(_), do: "Invalid datetime"
+  def format_datetime(_, _timezone), do: "Invalid datetime"
+
+  defp format_datetime_utc(%DateTime{} = dt) do
+    Calendar.strftime(dt, "%d.%m.%Y %H:%M")
+  end
 end

lib/mv_web/live/join_request_live/index.ex

@@ -63,7 +63,7 @@ defmodule MvWeb.JoinRequestLive.Index do
             >
               <:col :let={req} label={gettext("Submitted at")}>
                 <%= if req.submitted_at do %>
-                  {DateFormatter.format_datetime(req.submitted_at)}
+                  {DateFormatter.format_datetime(req.submitted_at, @browser_timezone)}
                 <% else %>
                   <.empty_cell sr_text={gettext("Not submitted yet")} />
                 <% end %>
@@ -125,7 +125,7 @@ defmodule MvWeb.JoinRequestLive.Index do
                 </.badge>
               </:col>
               <:col :let={req} label={gettext("Reviewed at")}>
-                {review_date(req)}
+                {review_date(req, @browser_timezone)}
               </:col>
               <:col :let={req} label={gettext("Review by")}>
                 {JoinRequestHelpers.reviewer_display(req) || ""}
@@ -162,7 +162,7 @@ defmodule MvWeb.JoinRequestLive.Index do
     assign(socket, :page_title, gettext("Join requests"))
   end
 
-  defp review_date(req) do
+  defp review_date(req, timezone) do
     date =
       case req.status do
         :approved -> req.approved_at
@@ -170,6 +170,6 @@ defmodule MvWeb.JoinRequestLive.Index do
         _ -> nil
       end
 
-    if date, do: DateFormatter.format_datetime(date), else: ""
+    if date, do: DateFormatter.format_datetime(date, timezone), else: ""
   end
 end

lib/mv_web/live/join_request_live/show.ex

@@ -144,7 +144,7 @@ defmodule MvWeb.JoinRequestLive.Show do
             <div class="border border-base-300 rounded-lg p-4 bg-base-100 space-y-2">
               <.field_row
                 label={gettext("Submitted at")}
-                value={DateFormatter.format_datetime(@join_request.submitted_at)}
+                value={DateFormatter.format_datetime(@join_request.submitted_at, @browser_timezone)}
               />
               <div class="flex gap-2">
                 <span class="text-base-content/60 min-w-32 shrink-0">{gettext("Status")}:</span>
@@ -158,13 +158,17 @@ defmodule MvWeb.JoinRequestLive.Show do
                 <%= if @join_request.approved_at do %>
                   <.field_row
                     label={gettext("Approved at")}
-                    value={DateFormatter.format_datetime(@join_request.approved_at)}
+                    value={
+                      DateFormatter.format_datetime(@join_request.approved_at, @browser_timezone)
+                    }
                   />
                 <% end %>
                 <%= if @join_request.rejected_at do %>
                   <.field_row
                     label={gettext("Rejected at")}
-                    value={DateFormatter.format_datetime(@join_request.rejected_at)}
+                    value={
+                      DateFormatter.format_datetime(@join_request.rejected_at, @browser_timezone)
+                    }
                   />
                 <% end %>
                 <.field_row

lib/mv_web/live_helpers.ex

@@ -22,6 +22,15 @@ defmodule MvWeb.LiveHelpers do
   def on_mount(:default, _params, session, socket) do
     locale = session["locale"] || "de"
     Gettext.put_locale(locale)
+
+    # Browser timezone from LiveSocket connect params (set in app.js via Intl API)
+    connect_params = socket.private[:connect_params] || %{}
+    timezone = connect_params["timezone"] || connect_params[:timezone]
+
+    socket =
+      socket
+      |> assign(:browser_timezone, timezone)
+
     {:cont, socket}
   end