Enhance quota management and refactor configuration handling

- Introduced `QuotaExceeded` settings in configuration to handle quota limits more effectively.
- Added preview model switching logic to `Client` to automatically use fallback models on quota exhaustion.
- Refactored `APIHandlers` to leverage new configuration structure.
- Simplified server initialization and removed redundant `ServerConfig` structure.
- Streamlined client initialization by unifying configuration handling throughout the project.
- Improved error handling and response mechanisms in both streaming and non-streaming flows.

internal/client/client.go

@@ -29,20 +29,29 @@ const (
 	pluginVersion      = "0.1.9"
 )
 
+var (
+	previewModels = map[string][]string{
+		"gemini-2.5-pro":   {"gemini-2.5-pro-preview-05-06", "gemini-2.5-pro-preview-06-05"},
+		"gemini-2.5-flash": {"gemini-2.5-flash-preview-04-17", "gemini-2.5-flash-preview-05-20"},
+	}
+)
+
 // Client is the main client for interacting with the CLI API.
 type Client struct {
-	httpClient   *http.Client
-	RequestMutex sync.Mutex
-	tokenStorage *auth.TokenStorage
-	cfg          *config.Config
+	httpClient         *http.Client
+	RequestMutex       sync.Mutex
+	tokenStorage       *auth.TokenStorage
+	cfg                *config.Config
+	modelQuotaExceeded map[string]*time.Time
 }
 
 // NewClient creates a new CLI API client.
 func NewClient(httpClient *http.Client, ts *auth.TokenStorage, cfg *config.Config) *Client {
 	return &Client{
-		httpClient:   httpClient,
-		tokenStorage: ts,
-		cfg:          cfg,
+		httpClient:         httpClient,
+		tokenStorage:       ts,
+		cfg:                cfg,
+		modelQuotaExceeded: make(map[string]*time.Time),
 	}
 }
 
@@ -214,97 +223,6 @@ func (c *Client) makeAPIRequest(ctx context.Context, endpoint, method string, bo
 	return nil
 }
 
-// SendMessageStream handles a single conversational turn, including tool calls.
-func (c *Client) SendMessageStream(ctx context.Context, rawJson []byte, model string, contents []Content, tools []ToolDeclaration) (<-chan []byte, <-chan *ErrorMessage) {
-	dataTag := []byte("data: ")
-	errChan := make(chan *ErrorMessage)
-	dataChan := make(chan []byte)
-	go func() {
-		defer close(errChan)
-		defer close(dataChan)
-
-		request := GenerateContentRequest{
-			Contents: contents,
-			GenerationConfig: GenerationConfig{
-				ThinkingConfig: GenerationConfigThinkingConfig{
-					IncludeThoughts: true,
-				},
-			},
-		}
-		request.Tools = tools
-
-		requestBody := map[string]interface{}{
-			"project": c.tokenStorage.ProjectID, // Assuming ProjectID is available
-			"request": request,
-			"model":   model,
-		}
-
-		byteRequestBody, _ := json.Marshal(requestBody)
-
-		// log.Debug(string(byteRequestBody))
-
-		reasoningEffortResult := gjson.GetBytes(rawJson, "reasoning_effort")
-		if reasoningEffortResult.String() == "none" {
-			byteRequestBody, _ = sjson.DeleteBytes(byteRequestBody, "request.generationConfig.thinkingConfig.include_thoughts")
-			byteRequestBody, _ = sjson.SetBytes(byteRequestBody, "request.generationConfig.thinkingConfig.thinkingBudget", 0)
-		} else if reasoningEffortResult.String() == "auto" {
-			byteRequestBody, _ = sjson.SetBytes(byteRequestBody, "request.generationConfig.thinkingConfig.thinkingBudget", -1)
-		} else if reasoningEffortResult.String() == "low" {
-			byteRequestBody, _ = sjson.SetBytes(byteRequestBody, "request.generationConfig.thinkingConfig.thinkingBudget", 1024)
-		} else if reasoningEffortResult.String() == "medium" {
-			byteRequestBody, _ = sjson.SetBytes(byteRequestBody, "request.generationConfig.thinkingConfig.thinkingBudget", 8192)
-		} else if reasoningEffortResult.String() == "high" {
-			byteRequestBody, _ = sjson.SetBytes(byteRequestBody, "request.generationConfig.thinkingConfig.thinkingBudget", 24576)
-		} else {
-			byteRequestBody, _ = sjson.SetBytes(byteRequestBody, "request.generationConfig.thinkingConfig.thinkingBudget", -1)
-		}
-
-		temperatureResult := gjson.GetBytes(rawJson, "temperature")
-		if temperatureResult.Exists() && temperatureResult.Type == gjson.Number {
-			byteRequestBody, _ = sjson.SetBytes(byteRequestBody, "request.generationConfig.temperature", temperatureResult.Num)
-		}
-
-		topPResult := gjson.GetBytes(rawJson, "top_p")
-		if topPResult.Exists() && topPResult.Type == gjson.Number {
-			byteRequestBody, _ = sjson.SetBytes(byteRequestBody, "request.generationConfig.topP", topPResult.Num)
-		}
-
-		topKResult := gjson.GetBytes(rawJson, "top_k")
-		if topKResult.Exists() && topKResult.Type == gjson.Number {
-			byteRequestBody, _ = sjson.SetBytes(byteRequestBody, "request.generationConfig.topK", topKResult.Num)
-		}
-
-		// log.Debug(string(byteRequestBody))
-
-		stream, err := c.APIRequest(ctx, "streamGenerateContent", byteRequestBody, true)
-		if err != nil {
-			// log.Println(err)
-			errChan <- err
-			return
-		}
-
-		scanner := bufio.NewScanner(stream)
-		for scanner.Scan() {
-			line := scanner.Bytes()
-			// log.Printf("Received stream chunk: %s", line)
-			if bytes.HasPrefix(line, dataTag) {
-				dataChan <- line[6:]
-			}
-		}
-
-		if errScanner := scanner.Err(); errScanner != nil {
-			// log.Println(err)
-			errChan <- &ErrorMessage{500, errScanner}
-			_ = stream.Close()
-			return
-		}
-
-		_ = stream.Close()
-	}()
-
-	return dataChan, errChan
-}
-
 // APIRequest handles making requests to the CLI API endpoints.
 func (c *Client) APIRequest(ctx context.Context, endpoint string, body interface{}, stream bool) (io.ReadCloser, *ErrorMessage) {
 	var jsonBody []byte
@@ -415,17 +333,192 @@ func (c *Client) SendMessage(ctx context.Context, rawJson []byte, model string,
 		byteRequestBody, _ = sjson.SetBytes(byteRequestBody, "request.generationConfig.topK", topKResult.Num)
 	}
 
+	modelName := model
 	// log.Debug(string(byteRequestBody))
+	for {
+		if c.isModelQuotaExceeded(modelName) {
+			if c.cfg.QuotaExceeded.SwitchPreviewModel {
+				modelName = c.getPreviewModel(model)
+				if modelName != "" {
+					log.Debugf("Model %s is quota exceeded. Switch to preview model %s", model, modelName)
+					byteRequestBody, _ = sjson.SetBytes(byteRequestBody, "model", modelName)
+					continue
+				}
+			}
+			return nil, &ErrorMessage{
+				StatusCode: 429,
+				Error:      fmt.Errorf(`{"error":{"code":429,"message":"All the models of '%s' are quota exceeded","status":"RESOURCE_EXHAUSTED"}}`, model),
+			}
+		}
 
-	respBody, err := c.APIRequest(ctx, "generateContent", byteRequestBody, false)
-	if err != nil {
-		return nil, err
+		respBody, err := c.APIRequest(ctx, "generateContent", byteRequestBody, false)
+		if err != nil {
+			if err.StatusCode == 429 {
+				now := time.Now()
+				c.modelQuotaExceeded[modelName] = &now
+				if c.cfg.QuotaExceeded.SwitchPreviewModel {
+					continue
+				}
+			}
+			return nil, err
+		}
+		delete(c.modelQuotaExceeded, modelName)
+		bodyBytes, errReadAll := io.ReadAll(respBody)
+		if errReadAll != nil {
+			return nil, &ErrorMessage{StatusCode: 500, Error: errReadAll}
+		}
+		return bodyBytes, nil
 	}
-	bodyBytes, errReadAll := io.ReadAll(respBody)
-	if errReadAll != nil {
-		return nil, &ErrorMessage{StatusCode: 500, Error: errReadAll}
+}
+
+// SendMessageStream handles a single conversational turn, including tool calls.
+func (c *Client) SendMessageStream(ctx context.Context, rawJson []byte, model string, contents []Content, tools []ToolDeclaration) (<-chan []byte, <-chan *ErrorMessage) {
+	dataTag := []byte("data: ")
+	errChan := make(chan *ErrorMessage)
+	dataChan := make(chan []byte)
+	go func() {
+		defer close(errChan)
+		defer close(dataChan)
+
+		request := GenerateContentRequest{
+			Contents: contents,
+			GenerationConfig: GenerationConfig{
+				ThinkingConfig: GenerationConfigThinkingConfig{
+					IncludeThoughts: true,
+				},
+			},
+		}
+		request.Tools = tools
+
+		requestBody := map[string]interface{}{
+			"project": c.tokenStorage.ProjectID, // Assuming ProjectID is available
+			"request": request,
+			"model":   model,
+		}
+
+		byteRequestBody, _ := json.Marshal(requestBody)
+
+		// log.Debug(string(byteRequestBody))
+
+		reasoningEffortResult := gjson.GetBytes(rawJson, "reasoning_effort")
+		if reasoningEffortResult.String() == "none" {
+			byteRequestBody, _ = sjson.DeleteBytes(byteRequestBody, "request.generationConfig.thinkingConfig.include_thoughts")
+			byteRequestBody, _ = sjson.SetBytes(byteRequestBody, "request.generationConfig.thinkingConfig.thinkingBudget", 0)
+		} else if reasoningEffortResult.String() == "auto" {
+			byteRequestBody, _ = sjson.SetBytes(byteRequestBody, "request.generationConfig.thinkingConfig.thinkingBudget", -1)
+		} else if reasoningEffortResult.String() == "low" {
+			byteRequestBody, _ = sjson.SetBytes(byteRequestBody, "request.generationConfig.thinkingConfig.thinkingBudget", 1024)
+		} else if reasoningEffortResult.String() == "medium" {
+			byteRequestBody, _ = sjson.SetBytes(byteRequestBody, "request.generationConfig.thinkingConfig.thinkingBudget", 8192)
+		} else if reasoningEffortResult.String() == "high" {
+			byteRequestBody, _ = sjson.SetBytes(byteRequestBody, "request.generationConfig.thinkingConfig.thinkingBudget", 24576)
+		} else {
+			byteRequestBody, _ = sjson.SetBytes(byteRequestBody, "request.generationConfig.thinkingConfig.thinkingBudget", -1)
+		}
+
+		temperatureResult := gjson.GetBytes(rawJson, "temperature")
+		if temperatureResult.Exists() && temperatureResult.Type == gjson.Number {
+			byteRequestBody, _ = sjson.SetBytes(byteRequestBody, "request.generationConfig.temperature", temperatureResult.Num)
+		}
+
+		topPResult := gjson.GetBytes(rawJson, "top_p")
+		if topPResult.Exists() && topPResult.Type == gjson.Number {
+			byteRequestBody, _ = sjson.SetBytes(byteRequestBody, "request.generationConfig.topP", topPResult.Num)
+		}
+
+		topKResult := gjson.GetBytes(rawJson, "top_k")
+		if topKResult.Exists() && topKResult.Type == gjson.Number {
+			byteRequestBody, _ = sjson.SetBytes(byteRequestBody, "request.generationConfig.topK", topKResult.Num)
+		}
+
+		// log.Debug(string(byteRequestBody))
+		modelName := model
+		var stream io.ReadCloser
+		for {
+			if c.isModelQuotaExceeded(modelName) {
+				if c.cfg.QuotaExceeded.SwitchPreviewModel {
+					modelName = c.getPreviewModel(model)
+					if modelName != "" {
+						log.Debugf("Model %s is quota exceeded. Switch to preview model %s", model, modelName)
+						byteRequestBody, _ = sjson.SetBytes(byteRequestBody, "model", modelName)
+						continue
+					}
+				}
+				errChan <- &ErrorMessage{
+					StatusCode: 429,
+					Error:      fmt.Errorf(`{"error":{"code":429,"message":"All the models of '%s' are quota exceeded","status":"RESOURCE_EXHAUSTED"}}`, model),
+				}
+				return
+			}
+			var err *ErrorMessage
+			stream, err = c.APIRequest(ctx, "streamGenerateContent", byteRequestBody, true)
+			if err != nil {
+				if err.StatusCode == 429 {
+					now := time.Now()
+					c.modelQuotaExceeded[modelName] = &now
+					if c.cfg.QuotaExceeded.SwitchPreviewModel {
+						continue
+					}
+				}
+				errChan <- err
+				return
+			}
+			delete(c.modelQuotaExceeded, modelName)
+			break
+		}
+
+		scanner := bufio.NewScanner(stream)
+		for scanner.Scan() {
+			line := scanner.Bytes()
+			// log.Printf("Received stream chunk: %s", line)
+			if bytes.HasPrefix(line, dataTag) {
+				dataChan <- line[6:]
+			}
+		}
+
+		if errScanner := scanner.Err(); errScanner != nil {
+			// log.Println(err)
+			errChan <- &ErrorMessage{500, errScanner}
+			_ = stream.Close()
+			return
+		}
+
+		_ = stream.Close()
+	}()
+
+	return dataChan, errChan
+}
+
+func (c *Client) isModelQuotaExceeded(model string) bool {
+	if lastExceededTime, hasKey := c.modelQuotaExceeded[model]; hasKey {
+		duration := time.Now().Sub(*lastExceededTime)
+		if duration > 30*time.Minute {
+			return false
+		}
+		return true
 	}
-	return bodyBytes, nil
+	return false
+}
+
+func (c *Client) getPreviewModel(model string) string {
+	if models, hasKey := previewModels[model]; hasKey {
+		for i := 0; i < len(models); i++ {
+			if !c.isModelQuotaExceeded(models[i]) {
+				return models[i]
+			}
+		}
+	}
+	return ""
+}
+
+func (c *Client) IsModelQuotaExceeded(model string) bool {
+	if c.isModelQuotaExceeded(model) {
+		if c.cfg.QuotaExceeded.SwitchPreviewModel {
+			return c.getPreviewModel(model) == ""
+		}
+		return true
+	}
+	return false
 }
 
 // CheckCloudAPIIsEnabled sends a simple test request to the API to verify