feat(rover-planning): warn when new site overlaps an existing 6-char grid

The add-rover-site form now resolves the input on every change and, if
any existing rover-location shares the same 6-char Maidenhead cell
(~5 km), surfaces a 'Already saved as' link to that location's detail
page. Avoids users accidentally duplicating a site they (or another
operator) already added.

lib/microwaveprop_web/live/rover_planning_live/show.ex

@@ -8,6 +8,7 @@ defmodule MicrowavepropWeb.RoverPlanningLive.Show do
 
   alias Microwaveprop.Accounts.User
   alias Microwaveprop.Radio.Maidenhead
+  alias Microwaveprop.Repo
   alias Microwaveprop.Rover
   alias Microwaveprop.Rover.Location
   alias Microwaveprop.RoverPlanning
@@ -35,7 +36,8 @@ defmodule MicrowavepropWeb.RoverPlanningLive.Show do
            mission: mission,
            paths: RoverPlanning.list_paths(mission),
            rover_sites: RoverPlanning.candidate_rover_locations(mission),
-           rover_site_input: ""
+           rover_site_input: "",
+           rover_site_input_matches: []
          )}
     end
   end
@@ -47,7 +49,11 @@ defmodule MicrowavepropWeb.RoverPlanningLive.Show do
 
   @impl true
   def handle_event("rover_site_input_change", %{"input" => input}, socket) do
-    {:noreply, assign(socket, rover_site_input: input)}
+    {:noreply,
+     assign(socket,
+       rover_site_input: input,
+       rover_site_input_matches: find_grid_matches(input)
+     )}
   end
 
   def handle_event("add_rover_site", %{"input" => input}, socket) do
@@ -97,7 +103,8 @@ defmodule MicrowavepropWeb.RoverPlanningLive.Show do
     |> assign(
       rover_sites: RoverPlanning.candidate_rover_locations(mission),
       paths: RoverPlanning.list_paths(mission),
-      rover_site_input: ""
+      rover_site_input: "",
+      rover_site_input_matches: []
     )
     |> put_flash(:info, flash_message)
   end
@@ -106,6 +113,30 @@ defmodule MicrowavepropWeb.RoverPlanningLive.Show do
 
   defp authenticated(_), do: {:error, :unauthenticated}
 
+  # Resolve the user-typed input and surface any existing rover-locations
+  # that share its 6-char Maidenhead grid (sub-grid resolution ≈ 5 km).
+  # Cheap enough for ~hundreds of locations: we map them in memory rather
+  # than maintaining a stored grid column.
+  defp find_grid_matches(input) when is_binary(input) do
+    trimmed = String.trim(input)
+
+    case trimmed != "" && LocationResolver.resolve(trimmed) do
+      {:ok, %{lat: lat, lon: lon}} when is_number(lat) and is_number(lon) ->
+        target = Maidenhead.from_latlon(lat, lon, 6)
+
+        Location
+        |> Repo.all()
+        |> Enum.filter(fn loc ->
+          Maidenhead.from_latlon(loc.lat, loc.lon, 6) == target
+        end)
+
+      _ ->
+        []
+    end
+  end
+
+  defp find_grid_matches(_), do: []
+
   defp can_modify?(%{current_scope: %{user: %User{is_admin: true}}}, _), do: true
 
   defp can_modify?(%{current_scope: %{user: %User{id: id}}}, %Mission{user_id: id}) when not is_nil(id), do: true
@@ -407,6 +438,18 @@ defmodule MicrowavepropWeb.RoverPlanningLive.Show do
           </button>
         </form>
 
+        <div :if={@rover_site_input_matches != []} class="mt-2 text-xs text-warning">
+          Already saved as:
+          <.link
+            :for={match <- @rover_site_input_matches}
+            navigate={~p"/rover-locations/#{match.id}"}
+            class="link link-warning font-mono ml-1"
+          >
+            {Maidenhead.from_latlon(match.lat, match.lon, 6)}{if match.notes && match.notes != "",
+              do: " (#{match.notes})"}
+          </.link>
+        </div>
+
         <p :if={!(@current_scope && @current_scope.user)} class="text-xs text-base-content/60">
           <.link navigate={~p"/users/log-in"} class="link">Sign in</.link>
           to add or remove rover sites.

test/microwaveprop_web/live/rover_planning_live_test.exs

@@ -409,6 +409,56 @@ defmodule MicrowavepropWeb.RoverPlanningLiveTest do
       assert Repo.aggregate(Location, :count) == 2
     end
 
+    test "typing a new rover site surfaces an existing match by 6-char grid",
+         %{conn: conn} do
+      user = AccountsFixtures.user_fixture()
+      mission = create_mission(user, "Match-existing mission")
+      conn = log_in_user(conn, user)
+
+      # Existing site at a known grid; the user-typed coords below
+      # land in the same 6-char Maidenhead cell, so the form should
+      # surface a link to the existing site rather than letting the
+      # user duplicate it.
+      {:ok, existing} =
+        Rover.create_location(user, %{
+          lat: 32.5,
+          lon: -97.5,
+          status: :good,
+          notes: "Existing parking spot"
+        })
+
+      {:ok, lv, _html} = live(conn, ~p"/rover-planning/#{mission.id}")
+
+      html =
+        lv
+        |> form("form[phx-submit='add_rover_site']", %{"input" => "32.5004, -97.4998"})
+        |> render_change()
+
+      # The 6-char grid for both points is identical, so a match link
+      # to the existing site appears with its grid label.
+      assert html =~ ~s(href="/rover-locations/#{existing.id})
+      grid6 = Maidenhead.from_latlon(32.5, -97.5, 6)
+      assert html =~ grid6
+    end
+
+    test "non-matching input shows no existing-site link", %{conn: conn} do
+      user = AccountsFixtures.user_fixture()
+      mission = create_mission(user, "No-match mission")
+      conn = log_in_user(conn, user)
+
+      {:ok, _other} =
+        Rover.create_location(user, %{lat: 32.5, lon: -97.5, status: :good})
+
+      {:ok, lv, _html} = live(conn, ~p"/rover-planning/#{mission.id}")
+
+      html =
+        lv
+        |> form("form[phx-submit='add_rover_site']", %{"input" => "45.0, -120.0"})
+        |> render_change()
+
+      refute html =~ "Already saved as"
+    end
+
     test "owner can remove a rover site from the show page", %{conn: conn} do
       user = AccountsFixtures.user_fixture()
       mission = create_mission(user, "Remove-site mission")