feat(server-go): 区域发病统计（#22，rooms.region + region-stats）

server-go/internal/service/region_stat.go

@@ -0,0 +1,44 @@
+package service
+
+import "sort"
+
+// RegionDiseaseEntry 区域发病条目（trace_records 联查 rooms 得到）
+type RegionDiseaseEntry struct {
+	Region  string
+	Disease string
+}
+
+// RegionStat 区域发病统计
+type RegionStat struct {
+	Region   string         `json:"region"`
+	Total    int            `json:"total"`
+	Diseases map[string]int `json:"diseases"`
+}
+
+// AggregateRegionStats 按区域分组统计发病数与病种分布（空区域剔除，按总数降序）
+func AggregateRegionStats(entries []RegionDiseaseEntry) []RegionStat {
+	byRegion := make(map[string]*RegionStat)
+	for _, e := range entries {
+		if e.Region == "" {
+			continue
+		}
+		s, ok := byRegion[e.Region]
+		if !ok {
+			s = &RegionStat{Region: e.Region, Diseases: map[string]int{}}
+			byRegion[e.Region] = s
+		}
+		s.Total++
+		s.Diseases[e.Disease]++
+	}
+	result := make([]RegionStat, 0, len(byRegion))
+	for _, s := range byRegion {
+		result = append(result, *s)
+	}
+	sort.Slice(result, func(i, j int) bool {
+		if result[i].Total != result[j].Total {
+			return result[i].Total > result[j].Total
+		}
+		return result[i].Region < result[j].Region
+	})
+	return result
+}

server-go/internal/service/region_stat_test.go

@@ -0,0 +1,32 @@
+package service
+
+import "testing"
+
+func TestAggregateRegionStats(t *testing.T) {
+	entries := []RegionDiseaseEntry{
+		{Region: "A镇", Disease: "白僵病"},
+		{Region: "A镇", Disease: "白僵病"},
+		{Region: "A镇", Disease: "软化病"},
+		{Region: "B乡", Disease: "白僵病"},
+		{Region: "", Disease: "白僵病"},
+	}
+	stats := AggregateRegionStats(entries)
+	if len(stats) != 2 {
+		t.Fatalf("统计区域数 = %d, want 2（空区域应剔除）", len(stats))
+	}
+	if stats[0].Region != "A镇" || stats[0].Total != 3 {
+		t.Errorf("A镇应排第一且 total=3，实际 %+v", stats[0])
+	}
+	if stats[0].Diseases["白僵病"] != 2 || stats[0].Diseases["软化病"] != 1 {
+		t.Errorf("A镇病种分布不正确: %+v", stats[0].Diseases)
+	}
+	if stats[1].Region != "B乡" || stats[1].Total != 1 {
+		t.Errorf("B乡统计不正确: %+v", stats[1])
+	}
+}
+
+func TestAggregateRegionStatsEmpty(t *testing.T) {
+	if len(AggregateRegionStats(nil)) != 0 {
+		t.Error("空输入应返回空结果")
+	}
+}