Cap "Contacts I'm in" at 100 most recent

The profile page's involving-contacts query now limits to the 100
most recent rows (ordered by qso_timestamp desc). A small note is
shown under the heading when the cap is hit so users know there's
more data they're not seeing.

lib/microwaveprop/radio.ex

@@ -129,8 +129,9 @@ defmodule Microwaveprop.Radio do
   end
 
   @doc """
-  Returns all contacts where the given callsign appears as either
-  `station1` or `station2`, newest first. Matching is case-insensitive.
+  Returns the 100 most recent contacts where the given callsign appears
+  as either `station1` or `station2`, newest first. Matching is
+  case-insensitive.
   """
   @spec list_contacts_involving_callsign(String.t() | nil) :: [Contact.t()]
   def list_contacts_involving_callsign(callsign) when callsign in [nil, ""], do: []
@@ -141,6 +142,7 @@ defmodule Microwaveprop.Radio do
     Contact
     |> where([c], fragment("upper(?)", c.station1) == ^upcased or fragment("upper(?)", c.station2) == ^upcased)
     |> order_by([c], desc: c.qso_timestamp, desc: c.id)
+    |> limit(100)
     |> Repo.all()
   end
 

lib/microwaveprop_web/live/user_profile_live.ex

@@ -159,6 +159,9 @@ defmodule MicrowavepropWeb.UserProfileLive do
           <%= if @involving == [] do %>
             <p class="text-sm opacity-70">No contacts on file with this callsign yet.</p>
           <% else %>
+            <p :if={length(@involving) == 100} class="text-xs opacity-60">
+              Showing the 100 most recent contacts.
+            </p>
             <div class="overflow-x-auto">
               <table class="table table-zebra table-sm">
                 <thead>

test/microwaveprop/radio_test.exs

@@ -552,5 +552,23 @@ defmodule Microwaveprop.RadioTest do
       assert Radio.list_contacts_involving_callsign("") == []
       assert Radio.list_contacts_involving_callsign(nil) == []
     end
+
+    test "caps the result at the 100 most recent contacts" do
+      base = ~U[2020-01-01 00:00:00Z]
+
+      for i <- 1..120 do
+        create_contact(%{
+          station1: "W5ISP",
+          station2: "K5X#{i}",
+          qso_timestamp: DateTime.add(base, i * 3600, :second)
+        })
+      end
+
+      result = Radio.list_contacts_involving_callsign("W5ISP")
+
+      assert length(result) == 100
+      # The 100 newest by qso_timestamp correspond to i = 21..120; i=120 is newest.
+      assert hd(result).station2 == "K5X120"
+    end
   end
 end