feat: make user limit configurable from admin user management (#18)

Store the per-instance user cap in settings (default 20) and expose
GET/PUT /admin/users/limit endpoints. The user management page now lets
admins view and update the limit without touching system settings.

Co-authored-by: Cursor Agent <cursoragent@cursor.com>
Co-authored-by: truewhile <truewhile@users.noreply.github.com>

internal/handler/admin.go

@@ -31,7 +31,66 @@ func listUsersHandler(svc *service.Container) gin.HandlerFunc {
 		for i := range users {
 			users[i].PopulateComputedFields()
 		}
-		c.JSON(http.StatusOK, users)
+		maxUsers, err := service.LoadMaxUsers(c.Request.Context(), svc.Repo)
+		if err != nil {
+			c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
+			return
+		}
+		c.JSON(http.StatusOK, gin.H{
+			"users":        users,
+			"max_users":    maxUsers,
+			"current_users": len(users),
+		})
+	}
+}
+
+type updateUserLimitReq struct {
+	MaxUsers int `json:"max_users" binding:"required"`
+}
+
+func getUserLimitHandler(svc *service.Container) gin.HandlerFunc {
+	return func(c *gin.Context) {
+		maxUsers, err := service.LoadMaxUsers(c.Request.Context(), svc.Repo)
+		if err != nil {
+			c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
+			return
+		}
+		currentUsers, err := svc.Repo.User.Count(c.Request.Context())
+		if err != nil {
+			c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
+			return
+		}
+		c.JSON(http.StatusOK, gin.H{
+			"max_users":     maxUsers,
+			"current_users": currentUsers,
+		})
+	}
+}
+
+func updateUserLimitHandler(svc *service.Container) gin.HandlerFunc {
+	return func(c *gin.Context) {
+		var req updateUserLimitReq
+		if err := c.ShouldBindJSON(&req); err != nil {
+			c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
+			return
+		}
+		if err := service.SaveMaxUsers(c.Request.Context(), svc.Repo, req.MaxUsers); err != nil {
+			if errors.Is(err, service.ErrInvalidMaxUsers) {
+				c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
+				return
+			}
+			c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
+			return
+		}
+		currentUsers, err := svc.Repo.User.Count(c.Request.Context())
+		if err != nil {
+			c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
+			return
+		}
+		c.JSON(http.StatusOK, gin.H{
+			"max_users":     req.MaxUsers,
+			"current_users": currentUsers,
+		})
 	}
 }
 
@@ -288,7 +347,12 @@ func writeUserMutationError(c *gin.Context, svc *service.Container, err error) {
 	case errors.Is(err, service.ErrUsernameTaken):
 		c.JSON(http.StatusConflict, gin.H{"error": "username already taken"})
 	case errors.Is(err, service.ErrUserLimitReached):
-		c.JSON(http.StatusBadRequest, gin.H{"error": "user limit reached", "max_users": service.UserLimit})
+		maxUsers, loadErr := service.LoadMaxUsers(c.Request.Context(), svc.Repo)
+		if loadErr != nil {
+			c.JSON(http.StatusInternalServerError, gin.H{"error": loadErr.Error()})
+			return
+		}
+		c.JSON(http.StatusBadRequest, gin.H{"error": "user limit reached", "max_users": maxUsers})
 	default:
 		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
 	}

internal/handler/admin_user_limit_test.go

@@ -0,0 +1,55 @@
+package handler
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"github.com/gin-gonic/gin"
+	"github.com/glebarez/sqlite"
+	"go.uber.org/zap"
+	"gorm.io/gorm"
+
+	"github.com/truewhile/MeBox/internal/model"
+	"github.com/truewhile/MeBox/internal/repository"
+	"github.com/truewhile/MeBox/internal/service"
+)
+
+func TestUserLimitHandlers(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	db, err := gorm.Open(sqlite.Open(":memory:"), &gorm.Config{})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := db.AutoMigrate(model.AllModels()...); err != nil {
+		t.Fatal(err)
+	}
+	repos := repository.New(db)
+	cfg := &service.Container{Repo: repos, Auth: service.NewAuthService(nil, zap.NewNop(), repos, service.NewTokenService(nil, zap.NewNop(), repos), service.NewPermissionService(zap.NewNop(), repos))}
+	router := gin.New()
+	router.GET("/admin/users/limit", getUserLimitHandler(cfg))
+	router.PUT("/admin/users/limit", updateUserLimitHandler(cfg))
+
+	req := httptest.NewRequest(http.MethodGet, "/admin/users/limit", nil)
+	w := httptest.NewRecorder()
+	router.ServeHTTP(w, req)
+	if w.Code != http.StatusOK {
+		t.Fatalf("GET limit status = %d body=%s", w.Code, w.Body.String())
+	}
+	if !strings.Contains(w.Body.String(), `"max_users":20`) {
+		t.Fatalf("expected default max_users=20, got %s", w.Body.String())
+	}
+
+	req = httptest.NewRequest(http.MethodPut, "/admin/users/limit", strings.NewReader(`{"max_users":42}`))
+	req.Header.Set("Content-Type", "application/json")
+	w = httptest.NewRecorder()
+	router.ServeHTTP(w, req)
+	if w.Code != http.StatusOK {
+		t.Fatalf("PUT limit status = %d body=%s", w.Code, w.Body.String())
+	}
+	got, err := service.LoadMaxUsers(t.Context(), repos)
+	if err != nil || got != 42 {
+		t.Fatalf("stored max users = %d err=%v, want 42", got, err)
+	}
+}

internal/handler/auth.go

@@ -68,6 +68,15 @@ func registerHandler(svc *service.Container) gin.HandlerFunc {
 				c.JSON(http.StatusConflict, gin.H{"error": "username taken"})
 				return
 			}
+			if errors.Is(err, service.ErrUserLimitReached) {
+				maxUsers, loadErr := service.LoadMaxUsers(c.Request.Context(), svc.Repo)
+				if loadErr != nil {
+					c.JSON(http.StatusInternalServerError, gin.H{"error": loadErr.Error()})
+					return
+				}
+				c.JSON(http.StatusBadRequest, gin.H{"error": "user limit reached", "max_users": maxUsers})
+				return
+			}
 			c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
 			return
 		}

internal/handler/emby_session_routes_test.go

@@ -213,10 +213,13 @@ func TestEmbyAuthenticatedRequestRefreshesRealtimeUserActivity(t *testing.T) {
 	if w.Code != http.StatusOK {
 		t.Fatalf("admin users status: %d body=%s", w.Code, w.Body.String())
 	}
-	var users []model.User
-	if err := json.Unmarshal(w.Body.Bytes(), &users); err != nil {
+	var payload struct {
+		Users []model.User `json:"users"`
+	}
+	if err := json.Unmarshal(w.Body.Bytes(), &payload); err != nil {
 		t.Fatalf("decode users: %v", err)
 	}
+	users := payload.Users
 	if len(users) != 1 {
 		t.Fatalf("users = %#v", users)
 	}

internal/handler/routes_admin.go

@@ -102,6 +102,8 @@ func registerAdminStrmRoutes(admin *gin.RouterGroup, svc *service.Container) {
 }
 
 func registerAdminUserRoutes(admin *gin.RouterGroup, svc *service.Container) {
+	admin.GET("/users/limit", getUserLimitHandler(svc))
+	admin.PUT("/users/limit", updateUserLimitHandler(svc))
 	admin.GET("/users", listUsersHandler(svc))
 	admin.POST("/users", createUserHandler(svc))
 	admin.PATCH("/users/:id", updateUserHandler(svc))