Link to existing contact on duplicate submission

Return the conflicting contact from create_contact so the UI can redirect
to it with a flash message instead of just showing a form error.

lib/microwaveprop/radio.ex

@@ -338,11 +338,8 @@ defmodule Microwaveprop.Radio do
       grid1 = Ecto.Changeset.get_change(changeset, :grid1)
       grid2 = Ecto.Changeset.get_change(changeset, :grid2)
 
-      if duplicate_contact_exists?(changeset) do
-        changeset =
-          Ecto.Changeset.add_error(changeset, :station1, "a matching contact already exists within the last hour")
-
-        {:error, %{changeset | action: :insert}}
+      if existing = find_duplicate_contact(changeset) do
+        {:error, :duplicate, existing}
       else
         case {Maidenhead.to_latlon(grid1), Maidenhead.to_latlon(grid2)} do
           {{:ok, {lat1, lon1}}, {:ok, {lat2, lon2}}} ->
@@ -365,7 +362,7 @@ defmodule Microwaveprop.Radio do
     end
   end
 
-  defp duplicate_contact_exists?(changeset) do
+  defp find_duplicate_contact(changeset) do
     s1 = Ecto.Changeset.get_field(changeset, :station1) |> to_string() |> String.upcase()
     s2 = Ecto.Changeset.get_field(changeset, :station2) |> to_string() |> String.upcase()
     g1 = Ecto.Changeset.get_field(changeset, :grid1) |> to_string() |> String.upcase()
@@ -377,8 +374,8 @@ defmodule Microwaveprop.Radio do
     min_ts = DateTime.add(ts, -@dedup_window_seconds, :second)
     max_ts = DateTime.add(ts, @dedup_window_seconds, :second)
 
-    # Query for contacts with same band in the time window, then check
-    # station/grid pair match (order-independent) in Elixir
+    expected_pair = Enum.sort([{s1, g1}, {s2, g2}])
+
     from(c in Contact,
       where:
         c.band == ^band_decimal and
@@ -387,11 +384,14 @@ defmodule Microwaveprop.Radio do
           c.flagged_invalid == false
     )
     |> Repo.all()
-    |> Enum.any?(fn c ->
-      a = {String.upcase(c.station1), String.upcase(c.grid1)}
-      b = {String.upcase(c.station2), String.upcase(c.grid2)}
-      pair = Enum.sort([a, b])
-      pair == Enum.sort([{s1, g1}, {s2, g2}])
+    |> Enum.find(fn c ->
+      pair =
+        Enum.sort([
+          {String.upcase(c.station1), String.upcase(c.grid1)},
+          {String.upcase(c.station2), String.upcase(c.grid2)}
+        ])
+
+      pair == expected_pair
     end)
   end
 

lib/microwaveprop_web/live/submit_live.ex

@@ -80,6 +80,15 @@ defmodule MicrowavepropWeb.SubmitLive do
            |> put_flash(:info, "Contact submitted successfully!")
            |> push_navigate(to: ~p"/contacts/#{contact.id}")}
 
+        {:error, :duplicate, existing} ->
+          {:noreply,
+           socket
+           |> put_flash(
+             :error,
+             "A matching contact already exists: #{existing.station1} ↔ #{existing.station2} on #{existing.band} MHz"
+           )
+           |> push_navigate(to: ~p"/contacts/#{existing.id}")}
+
         {:error, changeset} ->
           {:noreply, assign(socket, form: to_form(changeset))}
       end

test/microwaveprop/radio/contact_submission_test.exs

@@ -96,11 +96,10 @@ defmodule Microwaveprop.Radio.ContactSubmissionTest do
   describe "create_contact/1 deduplication" do
     alias Microwaveprop.Radio
 
-    test "rejects duplicate contact within 1-hour window" do
-      assert {:ok, _contact} = Radio.create_contact(@valid_attrs)
+    test "rejects duplicate and returns the existing contact" do
+      assert {:ok, original} = Radio.create_contact(@valid_attrs)
 
-      assert {:error, changeset} = Radio.create_contact(@valid_attrs)
-      assert "a matching contact already exists within the last hour" in errors_on(changeset).station1
+      assert {:error, :duplicate, ^original} = Radio.create_contact(@valid_attrs)
     end
 
     test "allows same stations on a different band" do
@@ -121,11 +120,10 @@ defmodule Microwaveprop.Radio.ContactSubmissionTest do
     end
 
     test "detects duplicates regardless of station order" do
-      assert {:ok, _} = Radio.create_contact(@valid_attrs)
+      assert {:ok, original} = Radio.create_contact(@valid_attrs)
 
       swapped = %{@valid_attrs | station1: "K5TR", grid1: "EM00", station2: "W5XD", grid2: "EM12"}
-      assert {:error, changeset} = Radio.create_contact(swapped)
-      assert "a matching contact already exists within the last hour" in errors_on(changeset).station1
+      assert {:error, :duplicate, ^original} = Radio.create_contact(swapped)
     end
   end
 end