Reduce admin dashboard read amplification

backend/internal/handler/admin/dashboard_handler_cache_test.go

@@ -0,0 +1,118 @@
+package admin
+
+import (
+	"context"
+	"net/http"
+	"net/http/httptest"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	"github.com/Wei-Shaw/sub2api/internal/pkg/usagestats"
+	"github.com/Wei-Shaw/sub2api/internal/service"
+	"github.com/gin-gonic/gin"
+	"github.com/stretchr/testify/require"
+)
+
+type dashboardUsageRepoCacheProbe struct {
+	service.UsageLogRepository
+	trendCalls      atomic.Int32
+	usersTrendCalls atomic.Int32
+}
+
+func (r *dashboardUsageRepoCacheProbe) GetUsageTrendWithFilters(
+	ctx context.Context,
+	startTime, endTime time.Time,
+	granularity string,
+	userID, apiKeyID, accountID, groupID int64,
+	model string,
+	requestType *int16,
+	stream *bool,
+	billingType *int8,
+) ([]usagestats.TrendDataPoint, error) {
+	r.trendCalls.Add(1)
+	return []usagestats.TrendDataPoint{{
+		Date:        "2026-03-11",
+		Requests:    1,
+		TotalTokens: 2,
+		Cost:        3,
+		ActualCost:  4,
+	}}, nil
+}
+
+func (r *dashboardUsageRepoCacheProbe) GetUserUsageTrend(
+	ctx context.Context,
+	startTime, endTime time.Time,
+	granularity string,
+	limit int,
+) ([]usagestats.UserUsageTrendPoint, error) {
+	r.usersTrendCalls.Add(1)
+	return []usagestats.UserUsageTrendPoint{{
+		Date:       "2026-03-11",
+		UserID:     1,
+		Email:      "cache@test.dev",
+		Requests:   2,
+		Tokens:     20,
+		Cost:       2,
+		ActualCost: 1,
+	}}, nil
+}
+
+func resetDashboardReadCachesForTest() {
+	dashboardTrendCache = newSnapshotCache(30 * time.Second)
+	dashboardUsersTrendCache = newSnapshotCache(30 * time.Second)
+	dashboardAPIKeysTrendCache = newSnapshotCache(30 * time.Second)
+	dashboardModelStatsCache = newSnapshotCache(30 * time.Second)
+	dashboardGroupStatsCache = newSnapshotCache(30 * time.Second)
+	dashboardSnapshotV2Cache = newSnapshotCache(30 * time.Second)
+}
+
+func TestDashboardHandler_GetUsageTrend_UsesCache(t *testing.T) {
+	t.Cleanup(resetDashboardReadCachesForTest)
+	resetDashboardReadCachesForTest()
+
+	gin.SetMode(gin.TestMode)
+	repo := &dashboardUsageRepoCacheProbe{}
+	dashboardSvc := service.NewDashboardService(repo, nil, nil, nil)
+	handler := NewDashboardHandler(dashboardSvc, nil)
+	router := gin.New()
+	router.GET("/admin/dashboard/trend", handler.GetUsageTrend)
+
+	req1 := httptest.NewRequest(http.MethodGet, "/admin/dashboard/trend?start_date=2026-03-01&end_date=2026-03-07&granularity=day", nil)
+	rec1 := httptest.NewRecorder()
+	router.ServeHTTP(rec1, req1)
+	require.Equal(t, http.StatusOK, rec1.Code)
+	require.Equal(t, "miss", rec1.Header().Get("X-Snapshot-Cache"))
+
+	req2 := httptest.NewRequest(http.MethodGet, "/admin/dashboard/trend?start_date=2026-03-01&end_date=2026-03-07&granularity=day", nil)
+	rec2 := httptest.NewRecorder()
+	router.ServeHTTP(rec2, req2)
+	require.Equal(t, http.StatusOK, rec2.Code)
+	require.Equal(t, "hit", rec2.Header().Get("X-Snapshot-Cache"))
+	require.Equal(t, int32(1), repo.trendCalls.Load())
+}
+
+func TestDashboardHandler_GetUserUsageTrend_UsesCache(t *testing.T) {
+	t.Cleanup(resetDashboardReadCachesForTest)
+	resetDashboardReadCachesForTest()
+
+	gin.SetMode(gin.TestMode)
+	repo := &dashboardUsageRepoCacheProbe{}
+	dashboardSvc := service.NewDashboardService(repo, nil, nil, nil)
+	handler := NewDashboardHandler(dashboardSvc, nil)
+	router := gin.New()
+	router.GET("/admin/dashboard/users-trend", handler.GetUserUsageTrend)
+
+	req1 := httptest.NewRequest(http.MethodGet, "/admin/dashboard/users-trend?start_date=2026-03-01&end_date=2026-03-07&granularity=day&limit=8", nil)
+	rec1 := httptest.NewRecorder()
+	router.ServeHTTP(rec1, req1)
+	require.Equal(t, http.StatusOK, rec1.Code)
+	require.Equal(t, "miss", rec1.Header().Get("X-Snapshot-Cache"))
+
+	req2 := httptest.NewRequest(http.MethodGet, "/admin/dashboard/users-trend?start_date=2026-03-01&end_date=2026-03-07&granularity=day&limit=8", nil)
+	rec2 := httptest.NewRecorder()
+	router.ServeHTTP(rec2, req2)
+	require.Equal(t, http.StatusOK, rec2.Code)
+	require.Equal(t, "hit", rec2.Header().Get("X-Snapshot-Cache"))
+	require.Equal(t, int32(1), repo.usersTrendCalls.Load())
+}