feat(rover): two-way grid <-> lat/lon sync on location form

Adds a Maidenhead grid input to the rover-location form. Typing a grid
fills in lat/lon (using square center); editing lat/lon recomputes the
grid at 6-char precision. The phx-change `_target` decides direction so
edits never clobber what the user just typed.

lib/microwaveprop_web/live/rover_locations_live.ex

@@ -56,6 +56,7 @@ defmodule MicrowavepropWeb.RoverLocationsLive do
        page_title: "Rover Locations",
        form: nil,
        editing_id: nil,
+       grid_input: "",
        status_filter: nil
      )
      |> assign(:data_provider, {__MODULE__, :visible_query_provider, [nil]})}
@@ -75,7 +76,7 @@ defmodule MicrowavepropWeb.RoverLocationsLive do
 
   def handle_event("new", _params, socket) do
     if user = current_user(socket) do
-      {:noreply, assign(socket, form: blank_form(user), editing_id: nil)}
+      {:noreply, assign(socket, form: blank_form(user), editing_id: nil, grid_input: "")}
     else
       {:noreply, put_flash(socket, :error, "Sign in to add a location.")}
     end
@@ -87,7 +88,8 @@ defmodule MicrowavepropWeb.RoverLocationsLive do
         case Repo.get(Location, id) do
           %Location{user_id: ^user_id} = loc ->
             cs = Location.changeset(loc, %{})
-            {:noreply, assign(socket, form: to_form(cs), editing_id: id)}
+            grid = Maidenhead.from_latlon(loc.lat, loc.lon, 6)
+            {:noreply, assign(socket, form: to_form(cs), editing_id: id, grid_input: grid)}
 
           _ ->
             {:noreply, put_flash(socket, :error, "You can only edit your own locations.")}
@@ -99,13 +101,16 @@ defmodule MicrowavepropWeb.RoverLocationsLive do
   end
 
   def handle_event("cancel", _, socket) do
-    {:noreply, assign(socket, form: nil, editing_id: nil)}
+    {:noreply, assign(socket, form: nil, editing_id: nil, grid_input: "")}
   end
 
-  def handle_event("validate", %{"location" => params}, socket) do
+  def handle_event("validate", %{"location" => params} = event_params, socket) do
+    target = event_params["_target"]
+    {params, grid_input} = sync_grid_and_latlon(params, target, socket.assigns.grid_input)
+
     base = if socket.assigns.editing_id, do: location_for_edit(socket), else: %Location{}
     cs = base |> Location.changeset(params) |> Map.put(:action, :validate)
-    {:noreply, assign(socket, form: to_form(cs))}
+    {:noreply, assign(socket, form: to_form(cs), grid_input: grid_input)}
   end
 
   def handle_event("save", %{"location" => params}, socket) do
@@ -201,6 +206,44 @@ defmodule MicrowavepropWeb.RoverLocationsLive do
   defp parse_status(value) when value in @valid_status_filters, do: value
   defp parse_status(_), do: nil
 
+  # Two-way grid <-> lat/lon sync. `_target` from the phx-change event
+  # tells us which field the user actually edited; we mirror the change
+  # into the other side. Unparseable input leaves the other side alone.
+  defp sync_grid_and_latlon(params, ["location", "grid"], _old_grid) do
+    raw = params |> Map.get("grid", "") |> to_string() |> String.trim()
+
+    case Maidenhead.to_latlon(raw) do
+      {:ok, {lat, lon}} ->
+        params =
+          params
+          |> Map.put("lat", format_coord(lat))
+          |> Map.put("lon", format_coord(lon))
+
+        {params, raw}
+
+      :error ->
+        {params, raw}
+    end
+  end
+
+  defp sync_grid_and_latlon(params, ["location", field], old_grid) when field in ["lat", "lon"] do
+    with {lat, ""} <- params |> Map.get("lat", "") |> to_string() |> String.trim() |> Float.parse(),
+         {lon, ""} <- params |> Map.get("lon", "") |> to_string() |> String.trim() |> Float.parse(),
+         lat when lat >= -90.0 and lat <= 90.0 <- lat,
+         lon when lon >= -180.0 and lon <= 180.0 <- lon do
+      grid = Maidenhead.from_latlon(lat, lon, 6)
+      {Map.put(params, "grid", grid), grid}
+    else
+      _ -> {params, old_grid}
+    end
+  end
+
+  defp sync_grid_and_latlon(params, _target, old_grid), do: {params, old_grid}
+
+  defp format_coord(value) do
+    value |> Float.round(6) |> Float.to_string()
+  end
+
   defp current_user(%Phoenix.LiveView.Socket{assigns: assigns}), do: scope_user(assigns)
   defp current_user(assigns) when is_map(assigns), do: scope_user(assigns)
 
@@ -325,7 +368,22 @@ defmodule MicrowavepropWeb.RoverLocationsLive do
           {if @editing_id, do: "Edit location", else: "New location"}
         </h2>
         <.form for={@form} phx-change="validate" phx-submit="save" id="location-form">
-          <div class="grid grid-cols-1 md:grid-cols-3 gap-3">
+          <div class="grid grid-cols-1 md:grid-cols-2 gap-3">
+            <.input
+              name="location[grid]"
+              value={@grid_input}
+              type="text"
+              label="Grid (Maidenhead)"
+              placeholder="EM12kp"
+            />
+            <.input
+              field={@form[:status]}
+              type="select"
+              label="Status"
+              options={[{"Ideal", :ideal}, {"Off Limits", :off_limits}]}
+            />
+          </div>
+          <div class="grid grid-cols-1 md:grid-cols-2 gap-3">
             <.input
               field={@form[:lat]}
               type="number"
@@ -340,12 +398,6 @@ defmodule MicrowavepropWeb.RoverLocationsLive do
               label="Longitude"
               placeholder="-97.5"
             />
-            <.input
-              field={@form[:status]}
-              type="select"
-              label="Status"
-              options={[{"Ideal", :ideal}, {"Off Limits", :off_limits}]}
-            />
           </div>
           <.input
             field={@form[:notes]}

test/microwaveprop_web/live/rover_locations_live_test.exs

@@ -79,6 +79,48 @@ defmodule MicrowavepropWeb.RoverLocationsLiveTest do
       assert html =~ "test note"
     end
 
+    test "typing a grid populates lat/lon", %{conn: conn} do
+      {:ok, lv, _html} = live(conn, ~p"/rover-locations")
+      lv |> element("button", "Add location") |> render_click()
+
+      html =
+        lv
+        |> form("#location-form",
+          location: %{
+            grid: "EM12kp",
+            lat: "",
+            lon: "",
+            status: "ideal",
+            notes: ""
+          }
+        )
+        |> render_change(%{"_target" => ["location", "grid"]})
+
+      # EM12kp center: lat 32.645833, lon -97.125
+      assert html =~ ~s(value="32.645833")
+      assert html =~ ~s(value="-97.125")
+    end
+
+    test "typing lat/lon populates the grid field", %{conn: conn} do
+      {:ok, lv, _html} = live(conn, ~p"/rover-locations")
+      lv |> element("button", "Add location") |> render_click()
+
+      html =
+        lv
+        |> form("#location-form",
+          location: %{
+            grid: "",
+            lat: "32.5",
+            lon: "-97.5",
+            status: "ideal",
+            notes: ""
+          }
+        )
+        |> render_change(%{"_target" => ["location", "lat"]})
+
+      assert html =~ ~s(value="EM12gm")
+    end
+
     test "edit/delete buttons appear only on the owner's row", %{conn: conn, user: user} do
       other = Microwaveprop.AccountsFixtures.user_fixture()
       {:ok, mine} = Rover.create_location(user, %{lat: 32.0, lon: -97.0, status: :ideal})