Add support for google-style reasoning

pkg/provider/google/google.go

@@ -21,6 +21,7 @@ type Client struct {
 
 type ContentPart struct {
 	Text         string            `json:"text,omitempty"`
+	Thought      bool              `json:"thought,omitempty"`
 	FunctionCall *FunctionCall     `json:"functionCall,omitempty"`
 	FunctionResp *FunctionResponse `json:"functionResponse,omitempty"`
 }
@@ -40,11 +41,18 @@ type Content struct {
 	Parts []ContentPart `json:"parts"`
 }
 
+type ThinkingConfig struct {
+	// Indicates whether to include thoughts in the response. If true, thoughts are returned
+	// only if the model supports thought and thoughts are available.
+	IncludeThoughts bool `json:"includeThoughts,omitempty"`
+}
+
 type GenerationConfig struct {
-	MaxOutputTokens *int     `json:"maxOutputTokens,omitempty"`
-	Temperature     *float32 `json:"temperature,omitempty"`
-	TopP            *float32 `json:"topP,omitempty"`
-	TopK            *int     `json:"topK,omitempty"`
+	MaxOutputTokens *int            `json:"maxOutputTokens,omitempty"`
+	Temperature     *float32        `json:"temperature,omitempty"`
+	TopP            *float32        `json:"topP,omitempty"`
+	TopK            *int            `json:"topK,omitempty"`
+	ThinkingConfig  *ThinkingConfig `json:"thinkingConfig,omitempty"`
 }
 
 type GenerateContentRequest struct {
@@ -241,6 +249,9 @@ func createGenerateContentRequest(
 			MaxOutputTokens: &params.MaxTokens,
 			Temperature:     &params.Temperature,
 			TopP:            &params.TopP,
+			ThinkingConfig: &ThinkingConfig{
+				IncludeThoughts: true,
+			},
 		},
 	}
 
@@ -363,7 +374,7 @@ func (c *Client) CreateChatCompletionStream(
 	}
 
 	url := fmt.Sprintf(
-		"%s/v1beta/models/%s:streamGenerateContent?key=%s&alt=sse",
+		"%s/v1alpha/models/%s:streamGenerateContent?key=%s&alt=sse",
 		c.BaseURL, params.Model, c.APIKey,
 	)
 	httpReq, err := http.NewRequestWithContext(ctx, "POST", url, bytes.NewBuffer(jsonData))
@@ -378,14 +389,14 @@ func (c *Client) CreateChatCompletionStream(
 	defer resp.Body.Close()
 
 	content := strings.Builder{}
+	reasoning := strings.Builder{}
+	var toolCalls []FunctionCall
 
 	lastMessage := messages[len(messages)-1]
 	if lastMessage.Role.IsAssistant() {
 		content.WriteString(lastMessage.Content)
 	}
 
-	var toolCalls []FunctionCall
-
 	reader := bufio.NewReader(resp.Body)
 
 	lastTokenCount := 0
@@ -416,14 +427,20 @@ func (c *Client) CreateChatCompletionStream(
 
 		choice := resp.Candidates[0]
 		for _, part := range choice.Content.Parts {
-			if part.FunctionCall != nil {
-				toolCalls = append(toolCalls, *part.FunctionCall)
+			if part.Thought {
+				output <- provider.Chunk{
+					ReasoningContent: part.Text,
+					TokenCount:       uint(tokens),
+				}
+				reasoning.WriteString(part.Text)
 			} else if part.Text != "" {
 				output <- provider.Chunk{
 					Content:    part.Text,
 					TokenCount: uint(tokens),
 				}
 				content.WriteString(part.Text)
+			} else if part.FunctionCall != nil {
+				toolCalls = append(toolCalls, *part.FunctionCall)
 			}
 		}
 	}
@@ -432,5 +449,5 @@ func (c *Client) CreateChatCompletionStream(
 		return api.NewMessageWithToolCalls(content.String(), convertToolCallToAPI(toolCalls)), nil
 	}
 
-	return api.NewMessageWithAssistant(content.String(), ""), nil
+	return api.NewMessageWithAssistant(content.String(), reasoning.String()), nil
 }