feat(core): implement group-based routing and optimize sync

Replace direct provider linkage with group-based routing for Keys and
Providers. This allows for more flexible load balancing and tiering
strategies.

Changes include:
- Remove `ProviderID` from Key model and DTO
- Add `Group` field to Key and Provider models
- Refactor Redis sync to use Hashes for O(1) partial updates
- Update API handlers to perform incremental syncs

BREAKING CHANGE: Key API payload no longer accepts `provider_id`. Redis
configuration storage format has changed from JSON strings to Hashes.

internal/api/handler.go

@@ -3,6 +3,7 @@ package api
 import (
 	"net/http"
 	"strconv"
+	"strings"
 
 	"github.com/ez-api/ez-api/internal/dto"
 	"github.com/ez-api/ez-api/internal/model"
@@ -28,9 +29,14 @@ func (h *Handler) CreateKey(c *gin.Context) {
 		return
 	}
 
+	group := strings.TrimSpace(req.Group)
+	if group == "" {
+		group = "default"
+	}
+
 	key := model.Key{
-		ProviderID: &req.ProviderID,
 		KeySecret: req.KeySecret,
+		Group:     group,
 		Balance:   req.Balance,
 		Status:    req.Status,
 		Weight:    req.Weight,
@@ -42,7 +48,7 @@ func (h *Handler) CreateKey(c *gin.Context) {
 	}
 
 	// Write auth hash and refresh snapshots
-	if err := h.sync.SyncAll(h.db); err != nil {
+	if err := h.sync.SyncKey(&key); err != nil {
 		c.JSON(http.StatusInternalServerError, gin.H{"error": "Failed to sync key to Redis", "details": err.Error()})
 		return
 	}
@@ -57,11 +63,17 @@ func (h *Handler) CreateProvider(c *gin.Context) {
 		return
 	}
 
+	group := strings.TrimSpace(req.Group)
+	if group == "" {
+		group = "default"
+	}
+
 	provider := model.Provider{
 		Name:    req.Name,
 		Type:    req.Type,
 		BaseURL: req.BaseURL,
 		APIKey:  req.APIKey,
+		Group:   group,
 	}
 
 	if err := h.db.Create(&provider).Error; err != nil {
@@ -69,7 +81,7 @@ func (h *Handler) CreateProvider(c *gin.Context) {
 		return
 	}
 
-	if err := h.sync.SyncAll(h.db); err != nil {
+	if err := h.sync.SyncProvider(&provider); err != nil {
 		c.JSON(http.StatusInternalServerError, gin.H{"error": "Failed to sync provider", "details": err.Error()})
 		return
 	}
@@ -100,7 +112,7 @@ func (h *Handler) CreateModel(c *gin.Context) {
 		return
 	}
 
-	if err := h.sync.SyncAll(h.db); err != nil {
+	if err := h.sync.SyncModel(&modelReq); err != nil {
 		c.JSON(http.StatusInternalServerError, gin.H{"error": "Failed to sync model", "details": err.Error()})
 		return
 	}
@@ -151,7 +163,7 @@ func (h *Handler) UpdateModel(c *gin.Context) {
 		return
 	}
 
-	if err := h.sync.SyncAll(h.db); err != nil {
+	if err := h.sync.SyncModel(&existing); err != nil {
 		c.JSON(http.StatusInternalServerError, gin.H{"error": "Failed to sync model", "details": err.Error()})
 		return
 	}

internal/dto/key.go

@@ -2,7 +2,7 @@ package dto
 
 // KeyDTO defines payload for key creation/update.
 type KeyDTO struct {
-    ProviderID uint    `json:"provider_id"`
+	Group     string  `json:"group"`
 	KeySecret string  `json:"key_secret"`
 	Balance   float64 `json:"balance"`
 	Status    string  `json:"status"`

internal/dto/provider.go

@@ -6,4 +6,5 @@ type ProviderDTO struct {
 	Type    string `json:"type"`
 	BaseURL string `json:"base_url"`
 	APIKey  string `json:"api_key"`
+	Group   string `json:"group"`
 }

internal/model/models.go

@@ -17,13 +17,13 @@ type Provider struct {
 	Type    string `gorm:"not null" json:"type"` // openai, anthropic, etc.
 	BaseURL string `json:"base_url"`
 	APIKey  string `json:"api_key"`
+	Group   string `gorm:"default:'default'" json:"group"` // routing group/tier
 }
 
 type Key struct {
 	gorm.Model
-	ProviderID *uint     `json:"provider_id"`
-	Provider   *Provider `json:"-"`
 	KeySecret string  `gorm:"not null" json:"key_secret"`
+	Group     string  `gorm:"default:'default'" json:"group"` // routing group/tier
 	Balance   float64 `json:"balance"`
 	Status    string  `gorm:"default:'active'" json:"status"` // active, suspended
 	Weight    int     `gorm:"default:10" json:"weight"`

internal/service/sync.go

@@ -6,6 +6,7 @@ import (
 	"encoding/hex"
 	"encoding/json"
 	"fmt"
+	"strings"
 
 	"github.com/ez-api/ez-api/internal/model"
 	"github.com/redis/go-redis/v9"
@@ -20,21 +21,62 @@ func NewSyncService(rdb *redis.Client) *SyncService {
 	return &SyncService{rdb: rdb}
 }
 
+// SyncKey writes a single key into Redis without rebuilding the entire snapshot.
 func (s *SyncService) SyncKey(key *model.Key) error {
-	tokenHash := hashToken(key.KeySecret)
-	redisKey := fmt.Sprintf("auth:token:%s", tokenHash)
+	ctx := context.Background()
+	snap := keySnapshot{
+		ID:        key.ID,
+		TokenHash: hashToken(key.KeySecret),
+		Group:     normalizeGroup(key.Group),
+		Status:    key.Status,
+		Weight:    key.Weight,
+		Balance:   key.Balance,
+	}
+
+	if err := s.hsetJSON(ctx, "config:keys", snap.TokenHash, snap); err != nil {
+		return err
+	}
 
 	fields := map[string]interface{}{
-		"status":  key.Status,
-		"balance": key.Balance,
+		"status":  snap.Status,
+		"group":   snap.Group,
+		"weight":  snap.Weight,
+		"balance": snap.Balance,
 	}
-	if key.ProviderID != nil {
-		fields["provider_id"] = *key.ProviderID
-	} else {
-		fields["provider_id"] = 0
+	if err := s.rdb.HSet(ctx, fmt.Sprintf("auth:token:%s", snap.TokenHash), fields).Err(); err != nil {
+		return fmt.Errorf("write auth token: %w", err)
+	}
+	return nil
 }
 
-	return s.rdb.HSet(context.Background(), redisKey, fields).Err()
+// SyncProvider writes a single provider into Redis hash storage.
+func (s *SyncService) SyncProvider(provider *model.Provider) error {
+	ctx := context.Background()
+	snap := providerSnapshot{
+		ID:      provider.ID,
+		Name:    provider.Name,
+		Type:    provider.Type,
+		BaseURL: provider.BaseURL,
+		APIKey:  provider.APIKey,
+		Group:   normalizeGroup(provider.Group),
+	}
+	return s.hsetJSON(ctx, "config:providers", fmt.Sprintf("%d", provider.ID), snap)
+}
+
+// SyncModel writes a single model metadata record.
+func (s *SyncService) SyncModel(m *model.Model) error {
+	ctx := context.Background()
+	snap := modelSnapshot{
+		Name:               m.Name,
+		ContextWindow:      m.ContextWindow,
+		CostPerToken:       m.CostPerToken,
+		SupportsVision:     m.SupportsVision,
+		SupportsFunction:   m.SupportsFunctions,
+		SupportsToolChoice: m.SupportsToolChoice,
+		SupportsFIM:        m.SupportsFIM,
+		MaxOutputTokens:    m.MaxOutputTokens,
+	}
+	return s.hsetJSON(ctx, "meta:models", snap.Name, snap)
 }
 
 type providerSnapshot struct {
@@ -43,12 +85,13 @@ type providerSnapshot struct {
 	Type    string `json:"type"`
 	BaseURL string `json:"base_url"`
 	APIKey  string `json:"api_key"`
+	Group   string `json:"group"`
 }
 
 type keySnapshot struct {
 	ID        uint    `json:"id"`
-	ProviderID uint    `json:"provider_id"`
 	TokenHash string  `json:"token_hash"`
+	Group     string  `json:"group"`
 	Status    string  `json:"status"`
 	Weight    int     `json:"weight"`
 	Balance   float64 `json:"balance"`
@@ -65,69 +108,68 @@ type modelSnapshot struct {
 	MaxOutputTokens    int     `json:"max_output_tokens"`
 }
 
-// SyncAll writes full snapshots (providers/keys/models) into Redis for DP consumption.
+// SyncAll rebuilds Redis hashes from the database; use for cold starts or forced refreshes.
 func (s *SyncService) SyncAll(db *gorm.DB) error {
 	ctx := context.Background()
 
-	// Providers snapshot
 	var providers []model.Provider
 	if err := db.Find(&providers).Error; err != nil {
 		return fmt.Errorf("load providers: %w", err)
 	}
-	providerSnap := make([]providerSnapshot, 0, len(providers))
+
+	var keys []model.Key
+	if err := db.Find(&keys).Error; err != nil {
+		return fmt.Errorf("load keys: %w", err)
+	}
+
+	var models []model.Model
+	if err := db.Find(&models).Error; err != nil {
+		return fmt.Errorf("load models: %w", err)
+	}
+
+	pipe := s.rdb.TxPipeline()
+	pipe.Del(ctx, "config:providers", "config:keys", "meta:models")
+
 	for _, p := range providers {
-		providerSnap = append(providerSnap, providerSnapshot{
+		snap := providerSnapshot{
 			ID:      p.ID,
 			Name:    p.Name,
 			Type:    p.Type,
 			BaseURL: p.BaseURL,
 			APIKey:  p.APIKey,
-		})
+			Group:   normalizeGroup(p.Group),
 		}
-	if err := s.storeJSON(ctx, "config:providers", providerSnap); err != nil {
-		return err
+		payload, err := json.Marshal(snap)
+		if err != nil {
+			return fmt.Errorf("marshal provider %d: %w", p.ID, err)
+		}
+		pipe.HSet(ctx, "config:providers", fmt.Sprintf("%d", p.ID), payload)
 	}
 
-	// Keys snapshot + auth hashes
-	var keys []model.Key
-	if err := db.Find(&keys).Error; err != nil {
-		return fmt.Errorf("load keys: %w", err)
-	}
-	keySnap := make([]keySnapshot, 0, len(keys))
 	for _, k := range keys {
-		tokenHash := hashToken(k.KeySecret)
-		keySnap = append(keySnap, keySnapshot{
+		snap := keySnapshot{
 			ID:        k.ID,
-			ProviderID: firstID(k.ProviderID),
-			TokenHash:  tokenHash,
+			TokenHash: hashToken(k.KeySecret),
+			Group:     normalizeGroup(k.Group),
 			Status:    k.Status,
 			Weight:    k.Weight,
 			Balance:   k.Balance,
+		}
+		payload, err := json.Marshal(snap)
+		if err != nil {
+			return fmt.Errorf("marshal key %d: %w", k.ID, err)
+		}
+		pipe.HSet(ctx, "config:keys", snap.TokenHash, payload)
+		pipe.HSet(ctx, fmt.Sprintf("auth:token:%s", snap.TokenHash), map[string]interface{}{
+			"status":  snap.Status,
+			"group":   snap.Group,
+			"weight":  snap.Weight,
+			"balance": snap.Balance,
 		})
-
-		// Maintain per-token auth hash for quick checks
-		fields := map[string]interface{}{
-			"status":      k.Status,
-			"provider_id": firstID(k.ProviderID),
-			"weight":      k.Weight,
-			"balance":     k.Balance,
-		}
-		if err := s.rdb.HSet(ctx, fmt.Sprintf("auth:token:%s", tokenHash), fields).Err(); err != nil {
-			return fmt.Errorf("write auth token: %w", err)
-		}
-	}
-	if err := s.storeJSON(ctx, "config:keys", keySnap); err != nil {
-		return err
 	}
 
-	// Models snapshot
-	var models []model.Model
-	if err := db.Find(&models).Error; err != nil {
-		return fmt.Errorf("load models: %w", err)
-	}
-	modelSnap := make([]modelSnapshot, 0, len(models))
 	for _, m := range models {
-		modelSnap = append(modelSnap, modelSnapshot{
+		snap := modelSnapshot{
 			Name:               m.Name,
 			ContextWindow:      m.ContextWindow,
 			CostPerToken:       m.CostPerToken,
@@ -136,22 +178,28 @@ func (s *SyncService) SyncAll(db *gorm.DB) error {
 			SupportsToolChoice: m.SupportsToolChoice,
 			SupportsFIM:        m.SupportsFIM,
 			MaxOutputTokens:    m.MaxOutputTokens,
-		})
 		}
-	if err := s.storeJSON(ctx, "meta:models", modelSnap); err != nil {
-		return err
+		payload, err := json.Marshal(snap)
+		if err != nil {
+			return fmt.Errorf("marshal model %s: %w", m.Name, err)
+		}
+		pipe.HSet(ctx, "meta:models", snap.Name, payload)
+	}
+
+	if _, err := pipe.Exec(ctx); err != nil {
+		return fmt.Errorf("write snapshots: %w", err)
 	}
 
 	return nil
 }
 
-func (s *SyncService) storeJSON(ctx context.Context, key string, val interface{}) error {
+func (s *SyncService) hsetJSON(ctx context.Context, key, field string, val interface{}) error {
 	payload, err := json.Marshal(val)
 	if err != nil {
-		return fmt.Errorf("marshal %s: %w", key, err)
+		return fmt.Errorf("marshal %s:%s: %w", key, field, err)
 	}
-	if err := s.rdb.Set(ctx, key, payload, 0).Err(); err != nil {
-		return fmt.Errorf("write %s: %w", key, err)
+	if err := s.rdb.HSet(ctx, key, field, payload).Err(); err != nil {
+		return fmt.Errorf("write %s:%s: %w", key, field, err)
 	}
 	return nil
 }
@@ -162,9 +210,9 @@ func hashToken(token string) string {
 	return hex.EncodeToString(hasher.Sum(nil))
 }
 
-func firstID(id *uint) uint {
-	if id == nil {
-		return 0
+func normalizeGroup(group string) string {
+	if strings.TrimSpace(group) == "" {
+		return "default"
 	}
-	return *id
+	return group
 }