From 4eca1aef709d0f1ac41d452b8c8992b40e1d27c0 Mon Sep 17 00:00:00 2001
From: RobertJoonas <56999674+RobertJoonas@users.noreply.github.com>
Date: Wed, 8 Mar 2023 13:45:04 +0200
Subject: [PATCH] fix a bug in percent change calculation (#2731)

---
 .../controllers/api/stats_controller.ex       |  4 +++-
 .../api/stats_controller/top_stats_test.exs   | 24 +++++++++++++++++++
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/lib/plausible_web/controllers/api/stats_controller.ex b/lib/plausible_web/controllers/api/stats_controller.ex
index 499f4f762..26fefc22e 100644
--- a/lib/plausible_web/controllers/api/stats_controller.ex
+++ b/lib/plausible_web/controllers/api/stats_controller.ex
@@ -427,6 +427,8 @@ defmodule PlausibleWeb.Api.StatsController do
     percent_change(old_count, new_count)
   end
 
+  defp percent_change(nil, _new_count), do: nil
+
   defp percent_change(old_count, new_count) do
     cond do
       old_count == 0 and new_count > 0 ->
@@ -1007,7 +1009,7 @@ defmodule PlausibleWeb.Api.StatsController do
     end
   end
 
-  defp calculate_cr(nil, _converted_visitors), do: 100.0
+  defp calculate_cr(nil, _converted_visitors), do: nil
 
   defp calculate_cr(unique_visitors, converted_visitors) do
     if unique_visitors > 0,
diff --git a/test/plausible_web/controllers/api/stats_controller/top_stats_test.exs b/test/plausible_web/controllers/api/stats_controller/top_stats_test.exs
index c6b295abe..b41da6896 100644
--- a/test/plausible_web/controllers/api/stats_controller/top_stats_test.exs
+++ b/test/plausible_web/controllers/api/stats_controller/top_stats_test.exs
@@ -419,5 +419,29 @@ defmodule PlausibleWeb.Api.StatsController.TopStatsTest do
 
       assert %{"name" => "Conversion rate", "value" => 33.3, "change" => 100} in res["top_stats"]
     end
+
+    test "returns conversion rate with change=nil when comparison mode disallowed", %{
+      conn: conn,
+      site: site
+    } do
+      populate_stats(site, [
+        build(:pageview, user_id: @user_id),
+        build(:pageview, user_id: @user_id),
+        build(:pageview),
+        build(:event, name: "Signup")
+      ])
+
+      filters = Jason.encode!(%{goal: "Signup"})
+
+      conn =
+        get(
+          conn,
+          "/api/stats/#{site.domain}/top-stats?period=all&filters=#{filters}"
+        )
+
+      res = json_response(conn, 200)
+
+      assert %{"name" => "Conversion rate", "value" => 33.3, "change" => nil} in res["top_stats"]
+    end
   end
 end