feat: 加入渠道加权随机功能

model/cache.go

@@ -198,6 +198,7 @@ func CacheGetRandomSatisfiedChannel(group string, model string) (*Channel, error
 		model = "gpt-4-gizmo-*"
 	}
 
+	// if memory cache is disabled, get channel directly from database
 	if !common.MemoryCacheEnabled {
 		return GetRandomSatisfiedChannel(group, model)
 	}
@@ -218,8 +219,29 @@ func CacheGetRandomSatisfiedChannel(group string, model string) (*Channel, error
 			}
 		}
 	}
-	idx := rand.Intn(endIdx)
-	return channels[idx], nil
+	// Calculate the total weight of all channels up to endIdx
+	totalWeight := 0
+	for _, channel := range channels[:endIdx] {
+		totalWeight += channel.GetWeight()
+	}
+
+	if totalWeight == 0 {
+		// If all weights are 0, select a channel randomly
+		return channels[rand.Intn(endIdx)], nil
+	}
+
+	// Generate a random value in the range [0, totalWeight)
+	randomWeight := rand.Intn(totalWeight)
+
+	// Find a channel based on its weight
+	for _, channel := range channels[:endIdx] {
+		randomWeight -= channel.GetWeight()
+		if randomWeight <= 0 {
+			return channel, nil
+		}
+	}
+	// return the last channel if no channel is found
+	return channels[endIdx-1], nil
 }
 
 func CacheGetChannel(id int) (*Channel, error) {