feat(map): shareable URL params for view/band/time

The main map page now reads band, selected time, and map
center/zoom from URL params and updates the URL as the user pans,
zooms, picks a band, or scrubs the timeline. Pan/zoom use
push_patch replace-mode so browser history isn't spammed, while
band and time changes push fresh entries.

Also fix the 'Up to date · just now ago' pipeline chip — 'just
now' already reads as an instant so the trailing 'ago' is
redundant. Any older duration keeps it.

assets/js/propagation_map_hook.ts

@@ -1503,11 +1503,15 @@ export const PropagationMap: Record<string, unknown> & {
     this.forecastCache.clear()
     // Pad bounds by ~0.5° so Leaflet edge tiles always have data to render
     const b = this.map.getBounds().pad(0.1)
+    const c = this.map.getCenter()
     this.pushEvent("map_bounds", {
       south: b.getSouth(),
       north: b.getNorth(),
       west: b.getWest(),
-      east: b.getEast()
+      east: b.getEast(),
+      center_lat: c.lat,
+      center_lon: c.lng,
+      zoom: this.map.getZoom()
     })
   },
 

lib/microwaveprop/propagation/pipeline_status.ex

@@ -131,21 +131,25 @@ defmodule Microwaveprop.Propagation.PipelineStatus do
     if age_minutes > @stale_after_minutes do
       %{
         state: :stale,
-        label: "Propagation data stale · last update #{format_age(age_minutes)} ago",
+        label: "Propagation data stale · last update #{format_age_with_ago(age_minutes)}",
         details: [],
         last_update_at: last
       }
     else
       %{
         state: :idle,
-        label: "Up to date · #{format_age(age_minutes)} ago",
+        label: "Up to date · #{format_age_with_ago(age_minutes)}",
         details: [],
         last_update_at: last
       }
     end
   end
 
-  defp format_age(0), do: "just now"
+  # "just now" reads fine on its own; anything older needs "ago" for
+  # the duration to make sense.
+  defp format_age_with_ago(0), do: "just now"
+  defp format_age_with_ago(n), do: "#{format_age(n)} ago"
+
   defp format_age(1), do: "1m"
   defp format_age(n) when n < 60, do: "#{n}m"
 

lib/microwaveprop_web/live/map_live.ex

@@ -29,7 +29,7 @@ defmodule MicrowavepropWeb.MapLive do
   @pipeline_status_refresh_ms 15_000
 
   @impl true
-  def mount(_params, session, socket) do
+  def mount(params, session, socket) do
     if connected?(socket) do
       Phoenix.PubSub.subscribe(Microwaveprop.PubSub, "propagation:updated")
       Phoenix.PubSub.subscribe(Microwaveprop.PubSub, "propagation:pipeline")
@@ -57,10 +57,10 @@ defmodule MicrowavepropWeb.MapLive do
       end
 
     bands = BandConfig.all_bands()
-    selected_band = recovered_band || @default_band
-    valid_times = Propagation.available_valid_times(selected_band)
-    selected_time = recovered_time || closest_to_now(valid_times)
-    center = initial_center(session)
+
+    %{band: selected_band, time: selected_time, center: center, zoom: zoom, valid_times: valid_times} =
+      resolve_view(params, session, recovered_band, recovered_time)
+
     visitor = visitor_location(session)
     bounds = bounds_around(center)
     initial_scores = Propagation.scores_at(selected_band, selected_time, bounds)
@@ -83,7 +83,9 @@ defmodule MicrowavepropWeb.MapLive do
        selected_time: selected_time,
        bounds: bounds,
        initial_center: center,
-       initial_zoom: @default_zoom,
+       initial_zoom: zoom,
+       current_center: center,
+       current_zoom: zoom,
        outside_conus: outside_conus?(visitor),
        grid_visible: false,
        radar_visible: false,
@@ -132,6 +134,18 @@ defmodule MicrowavepropWeb.MapLive do
       lon < @conus_lon_min or lon > @conus_lon_max
   end
 
+  # Resolve the initial band/time/center/zoom from URL params, falling
+  # back to LiveStash recovery, then session geolocation and defaults.
+  defp resolve_view(params, session, recovered_band, recovered_time) do
+    band = parse_band_param(params["band"]) || recovered_band || @default_band
+    valid_times = Propagation.available_valid_times(band)
+    time = parse_time_param(params["t"]) || recovered_time || closest_to_now(valid_times)
+    center = parse_center_param(params["lat"], params["lon"]) || initial_center(session)
+    zoom = parse_zoom_param(params["zoom"]) || @default_zoom
+
+    %{band: band, time: time, center: center, zoom: zoom, valid_times: valid_times}
+  end
+
   # Build a bounding box roughly matching the hardcoded default (~3.4° × 9°)
   # around a given center so the initial HRRR score query still returns a
   # useful tile set for the visible area.
@@ -144,6 +158,14 @@ defmodule MicrowavepropWeb.MapLive do
     }
   end
 
+  @impl true
+  def handle_params(_params, _url, socket) do
+    # URL params are applied in mount/3; subsequent push_patch calls
+    # hit this callback with the same params that our own push_patch
+    # just wrote, so there's nothing further to reconcile here.
+    {:noreply, socket}
+  end
+
   @impl true
   def handle_event("select_band", %{"value" => band}, socket) do
     band = if is_binary(band), do: String.to_integer(band), else: band
@@ -160,6 +182,7 @@ defmodule MicrowavepropWeb.MapLive do
       |> push_event("update_scores", %{scores: scores})
       |> push_event("update_band_info", %{band_info: band_info(band)})
       |> push_timeline()
+      |> patch_map_url()
 
     {:noreply, socket}
   end
@@ -173,6 +196,7 @@ defmodule MicrowavepropWeb.MapLive do
           socket
           |> assign(:selected_time, time)
           |> push_event("update_scores", %{scores: scores})
+          |> patch_map_url()
 
         {:noreply, socket}
 
@@ -186,8 +210,11 @@ defmodule MicrowavepropWeb.MapLive do
   # (used later for point_detail and forecast state on reconnect).
   def handle_event("set_selected_time", %{"time" => time_str}, socket) do
     case DateTime.from_iso8601(time_str) do
-      {:ok, time, _} -> {:noreply, assign(socket, :selected_time, time)}
-      _ -> {:noreply, socket}
+      {:ok, time, _} ->
+        {:noreply, socket |> assign(:selected_time, time) |> patch_map_url()}
+
+      _ ->
+        {:noreply, socket}
     end
   end
 
@@ -246,7 +273,9 @@ defmodule MicrowavepropWeb.MapLive do
     socket =
       socket
       |> assign(:bounds, bounds)
+      |> maybe_assign_center_zoom(bounds)
       |> push_event("update_scores", %{scores: scores})
+      |> patch_map_url(replace: true)
 
     {:noreply, socket}
   end
@@ -414,6 +443,83 @@ defmodule MicrowavepropWeb.MapLive do
     "#{hours}h ago"
   end
 
+  # --- URL param plumbing -----------------------------------------------
+
+  # The JS hook piggybacks map center + zoom onto the bounds event
+  # so the URL can carry a shareable view. Old payloads (no center)
+  # should still work — fall back to keeping whatever we had.
+  defp maybe_assign_center_zoom(socket, %{"center_lat" => lat, "center_lon" => lon, "zoom" => zoom})
+       when is_number(lat) and is_number(lon) and is_number(zoom) do
+    assign(socket, current_center: %{lat: lat, lon: lon}, current_zoom: trunc(zoom))
+  end
+
+  defp maybe_assign_center_zoom(socket, _), do: socket
+
+  defp patch_map_url(socket, opts \\ []) do
+    push_patch(socket, to: map_url(socket.assigns), replace: Keyword.get(opts, :replace, false))
+  end
+
+  defp map_url(assigns) do
+    params =
+      %{}
+      |> Map.put("band", assigns.selected_band)
+      |> put_if(assigns.selected_time, "t", fn dt -> DateTime.to_iso8601(dt) end)
+      |> put_if(assigns[:current_center], "lat", fn c -> Float.round(c.lat, 3) end)
+      |> put_if(assigns[:current_center], "lon", fn c -> Float.round(c.lon, 3) end)
+      |> put_if(assigns[:current_zoom], "zoom", fn z -> trunc(z) end)
+
+    "/map?" <> URI.encode_query(params)
+  end
+
+  defp put_if(map, nil, _key, _fun), do: map
+  defp put_if(map, value, key, fun), do: Map.put(map, key, fun.(value))
+
+  @doc false
+  def parse_band_param(nil), do: nil
+
+  def parse_band_param(str) when is_binary(str) do
+    case Integer.parse(str) do
+      {n, ""} -> if BandConfig.get(n), do: n
+      _ -> nil
+    end
+  end
+
+  @doc false
+  def parse_time_param(nil), do: nil
+
+  def parse_time_param(str) when is_binary(str) do
+    case DateTime.from_iso8601(str) do
+      {:ok, dt, _} -> DateTime.truncate(dt, :second)
+      _ -> nil
+    end
+  end
+
+  @doc false
+  def parse_center_param(lat_s, lon_s) when is_binary(lat_s) and is_binary(lon_s) do
+    with {lat, ""} <- Float.parse(lat_s),
+         {lon, ""} <- Float.parse(lon_s),
+         true <- lat >= -90.0 and lat <= 90.0,
+         true <- lon >= -180.0 and lon <= 180.0 do
+      %{lat: lat, lon: lon}
+    else
+      _ -> nil
+    end
+  end
+
+  def parse_center_param(_, _), do: nil
+
+  @doc false
+  def parse_zoom_param(nil), do: nil
+
+  def parse_zoom_param(str) when is_binary(str) do
+    case Integer.parse(str) do
+      {n, ""} when n >= 1 and n <= 18 -> n
+      _ -> nil
+    end
+  end
+
+  # --- end URL param plumbing -------------------------------------------
+
   defp closest_to_now(times), do: cursor_for_now(times, DateTime.utc_now())
 
   @doc false
@@ -566,6 +672,7 @@ defmodule MicrowavepropWeb.MapLive do
             )
           }
           data-selected-time={if @selected_time, do: DateTime.to_iso8601(@selected_time), else: ""}
+          data-selected-band={@selected_band}
           data-center-lat={@initial_center.lat}
           data-center-lon={@initial_center.lon}
           data-zoom={@initial_zoom}

test/microwaveprop/propagation/pipeline_status_test.exs

@@ -114,6 +114,20 @@ defmodule Microwaveprop.Propagation.PipelineStatusTest do
       assert status.label =~ "Up to date"
     end
 
+    test "drops the 'ago' suffix when the data is brand new" do
+      ScoresFile.write!(
+        10_000,
+        DateTime.utc_now(),
+        [%{lat: 25.0, lon: -125.0, score: 50}]
+      )
+
+      status = PipelineStatus.current()
+
+      assert status.state == :idle
+      assert status.label =~ "Up to date · just now"
+      refute status.label =~ "just now ago"
+    end
+
     test "returns :stale when the newest ScoresFile is more than 120 minutes old" do
       ScoresFile.write!(
         10_000,

test/microwaveprop_web/live/map_live_test.exs

@@ -128,6 +128,25 @@ defmodule MicrowavepropWeb.MapLiveTest do
     end
   end
 
+  describe "URL params" do
+    test "band URL param selects the requested band on mount", %{conn: conn} do
+      {:ok, _lv, html} = live(conn, ~p"/map?band=24000")
+      assert html =~ ~s(data-selected-band="24000")
+    end
+
+    test "lat/lon/zoom URL params override the default map center/zoom", %{conn: conn} do
+      {:ok, _lv, html} = live(conn, ~p"/map?lat=40.0&lon=-100.0&zoom=5")
+      assert html =~ ~s(data-center-lat="40.0")
+      assert html =~ ~s(data-center-lon="-100.0")
+      assert html =~ ~s(data-zoom="5")
+    end
+
+    test "invalid band falls back to the default", %{conn: conn} do
+      {:ok, _lv, html} = live(conn, ~p"/map?band=notanumber")
+      assert html =~ ~s(data-selected-band="10000")
+    end
+  end
+
   describe "cursor_for_now/2" do
     alias MicrowavepropWeb.MapLive