From a05e708085edb8dbac9211ff2f148a4d1fd3274e Mon Sep 17 00:00:00 2001
From: Kalle <38327916+Sendouc@users.noreply.github.com>
Date: Fri, 16 Oct 2026 17:38:36 +0300
Subject: [PATCH] Fix division SPR comparing against tournament-wide seeds

---
 .../tournament/core/Standings.test.ts         | 21 +++++++++++++++----
 app/features/tournament/core/Standings.ts     | 11 +++++++++-
 changelog/2026-10-16-division-spr.md          |  5 +++++
 3 files changed, 32 insertions(+), 5 deletions(-)
 create mode 100644 changelog/2026-10-16-division-spr.md

diff --git a/app/features/tournament/core/Standings.test.ts b/app/features/tournament/core/Standings.test.ts
index 994e7c53c..3ca4c1c12 100644
--- a/app/features/tournament/core/Standings.test.ts
+++ b/app/features/tournament/core/Standings.test.ts
@@ -312,16 +312,29 @@ describe("sprByTeamId", () => {
 		expect(result.get(4)).toBe(0);
 	});
 
-	test("returns 0 for a team whose seed is outside the standings", () => {
+	test("returns 0 for a team without a seed", () => {
 		const result = sprByTeamId(
 			standings([
-				{ id: 1, seed: 1, placement: 1 },
-				{ id: 2, seed: 9, placement: 2 },
+				{ id: 2, seed: null, placement: 1 },
+				{ id: 1, seed: 1, placement: 2 },
 			]),
 		);
 
 		expect(result.get(2)).toBe(0);
 	});
+
+	test("compares a division's teams by their seed order within that division", () => {
+		// division B of an A/B divisions tournament, seeds 1 & 3 went to division A
+		const result = sprByTeamId(
+			standings([
+				{ id: 4, seed: 4, placement: 1 },
+				{ id: 2, seed: 2, placement: 2 },
+			]),
+		);
+
+		expect(result.get(4)).toBe(1);
+		expect(result.get(2)).toBe(-1);
+	});
 });
 
 describe("winners", () => {
@@ -976,7 +989,7 @@ function playOut(
 }
 
 function standings(
-	teams: Array<{ id: number; seed: number; placement: number }>,
+	teams: Array<{ id: number; seed: number | null; placement: number }>,
 ): Standing[] {
 	return teams.map(({ id, seed, placement }) => ({
 		team: tournamentCtxTeam(id, { seed }),
diff --git a/app/features/tournament/core/Standings.ts b/app/features/tournament/core/Standings.ts
index 8e0dc2456..2ea05344a 100644
--- a/app/features/tournament/core/Standings.ts
+++ b/app/features/tournament/core/Standings.ts
@@ -66,6 +66,7 @@ export function reNumberPlacements<T extends { placement: number }>(
 
 /**
  * SPR (Seed Performance Rating) of every team in the standings, keyed by tournament team id.
+ * Seeds are ranked among the given standings only, so a division's standings are compared to its own seed order.
  * See https://web.archive.org/web/20250513034545/https://www.pgstats.com/articles/introducing-spr-and-uf
  */
 export function sprByTeamId(standings: Standing[]): Map<number, number> {
@@ -75,11 +76,19 @@ export function sprByTeamId(standings: Standing[]): Map<number, number> {
 			.map((placement, index) => [placement, index]),
 	);
 
+	const seedRankByTeamId = new Map(
+		R.sortBy(
+			standings.filter((standing) => typeof standing.team.seed === "number"),
+			(standing) => standing.team.seed ?? 0,
+		).map((standing, rank) => [standing.team.id, rank]),
+	);
+
 	const result = new Map<number, number>();
 
 	for (const standing of standings) {
+		const seedRank = seedRankByTeamId.get(standing.team.id);
 		const expectedPlacement =
-			standings[(standing.team.seed ?? 0) - 1]?.placement;
+			typeof seedRank === "number" ? standings[seedRank]?.placement : undefined;
 		const expectedIndex = expectedPlacement
 			? indexByPlacement.get(expectedPlacement)
 			: undefined;
diff --git a/changelog/2026-10-16-division-spr.md b/changelog/2026-10-16-division-spr.md
new file mode 100644
index 000000000..1afe1cc26
--- /dev/null
+++ b/changelog/2026-10-16-division-spr.md
@@ -0,0 +1,5 @@
+---
+navItem: medal
+type: bug
+---
+Fixed tournament results showing the wrong SPR for teams in A/B divisions