From 641e51c887667b865a54ff9ccfb5f8c0c0ee30d9 Mon Sep 17 00:00:00 2001
From: JianMiau <bir840124@gmail.com>
Date: Mon, 10 Aug 2026 15:47:38 +0800
Subject: [PATCH] =?UTF-8?q?=E5=8A=9F=E8=83=BD=EF=BC=9A=E6=89=8B=E5=8B=95?=
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根本原因：
原本配對只以人數多的一區為基準，缺額全部補「輪空」。例如 A 區 7 人、B 區 5 人會補 2 個輪空，但總人數 12 是偶數，其實可以讓 A 區 1 人跨區支援就湊滿 6 隊真人對打。

影響：
兩區差距 2 以上時，每輪自動抽「差距÷2」人跨區支援，且每輪輪替不同人，跨區負擔平均分攤；只有總人數為奇數時才會補 1 個輪空。等人數時行為不變，三輪之間照舊旋轉配對讓搭檔不同。

修法：
自 badminton-match-hub 8cc0518 移植 balanceZones / pickCrossMembers，buildManualGroups 改為每輪先平衡兩區再建隊伍，補位改在平衡後只補至多 1 個。

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
---
 src/lib/match.ts | 58 ++++++++++++++++++++++++++++++++++++++----------
 1 file changed, 46 insertions(+), 12 deletions(-)

diff --git a/src/lib/match.ts b/src/lib/match.ts
index c06e890..d0f3318 100644
--- a/src/lib/match.ts
+++ b/src/lib/match.ts
@@ -22,22 +22,56 @@ export function parseRoster(input: string) {
 }
 
 export function buildManualGroups(areaA: string[], areaB: string[]) {
-  const targetCount = Math.max(areaA.length, areaB.length)
   const shuffledA = shuffleList(areaA)
   const shuffledB = shuffleList(areaB)
-  const paddedA = padTeams(shuffledA, targetCount)
-  const paddedB = padTeams(shuffledB, targetCount)
 
-  return Array.from({ length: TOTAL_GROUPS }, (_, roundIndex) => ({
-    id: roundIndex + 1,
-    teams: paddedA.map((playerA, index) =>
-      createTeam(
-        index + 1,
-        playerA,
-        paddedB[(index + roundIndex) % paddedB.length],
+  // 每輪先做跨區平衡再配對：兩區差距 2 以上時抽「差距÷2」人跨區支援，
+  // 且每輪輪替不同人；只有總人數為奇數時才會補 1 個輪空。
+  return Array.from({ length: TOTAL_GROUPS }, (_, roundIndex) => {
+    const balanced = balanceZones(shuffledA, shuffledB, roundIndex)
+    const targetCount = Math.max(balanced.areaA.length, balanced.areaB.length)
+    const paddedA = padTeams(balanced.areaA, targetCount)
+    const paddedB = padTeams(balanced.areaB, targetCount)
+
+    return {
+      id: roundIndex + 1,
+      teams: paddedA.map((playerA, index) =>
+        createTeam(
+          index + 1,
+          playerA,
+          paddedB[(index + roundIndex) % paddedB.length],
+        ),
       ),
-    ),
-  }))
+    }
+  })
+}
+
+function balanceZones(areaA: string[], areaB: string[], roundIndex: number) {
+  const moveCount = Math.floor(Math.abs(areaA.length - areaB.length) / 2)
+
+  if (moveCount === 0) {
+    return { areaA, areaB }
+  }
+
+  if (areaA.length > areaB.length) {
+    const { moved, remaining } = pickCrossMembers(areaA, moveCount, roundIndex)
+    return { areaA: remaining, areaB: [...areaB, ...moved] }
+  }
+
+  const { moved, remaining } = pickCrossMembers(areaB, moveCount, roundIndex)
+  return { areaA: [...areaA, ...moved], areaB: remaining }
+}
+
+// 依輪次輪替抽出要跨區支援的人，讓跨區的負擔平均分攤在不同人身上。
+function pickCrossMembers(list: string[], moveCount: number, roundIndex: number) {
+  const movedIndexes = new Set(
+    Array.from({ length: moveCount }, (_, offset) => (roundIndex * moveCount + offset) % list.length),
+  )
+
+  return {
+    moved: list.filter((_, index) => movedIndexes.has(index)),
+    remaining: list.filter((_, index) => !movedIndexes.has(index)),
+  }
 }
 
 export function convertDbRecordToGroups(record: MatchResultsRecord) {