Add working adk code

docs/en/samples/pre_post_processing/go/adk/agent.go

@@ -0,0 +1,172 @@
+/*
+ * Copyright 2026 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package main
+
+import (
+	"context"
+	"fmt"
+	"log"
+	"os"
+	"strings"
+	"time"
+
+	"github.com/googleapis/mcp-toolbox-sdk-go/tbadk"
+	"google.golang.org/adk/agent"
+	"google.golang.org/adk/agent/llmagent"
+	"google.golang.org/adk/model/gemini"
+	"google.golang.org/adk/runner"
+	"google.golang.org/adk/session"
+	"google.golang.org/adk/tool"
+	"google.golang.org/genai"
+)
+
+const systemPrompt = `
+  You're a helpful hotel assistant. You handle hotel searching, booking and
+  cancellations. When the user searches for a hotel, mention it's name, id,
+  location and price tier. Always mention hotel ids while performing any
+  searches. This is very important for any operations. For any bookings or
+  cancellations, please provide the appropriate confirmation. Be sure to
+  update checkin or checkout dates if mentioned by the user.
+  Don't ask for confirmations from the user.
+`
+
+var queries = []string{
+	"Book hotel with id 3.",
+	"Update my hotel with id 3 with checkin date 2025-01-04 and checkout date 2025-01-20",
+}
+
+// Pre-processing
+func beforeToolCallback(ctx tool.Context, tool tool.Tool, args map[string]any) (map[string]any, error) {
+
+	fmt.Printf("POLICY CHECK: Intercepting '%s'\n", tool.Name())
+	if tool.Name() == "update-hotel" {
+		checkinStr, okCheckin := args["checkin_date"].(string)
+		checkoutStr, okCheckout := args["checkout_date"].(string)
+
+		if okCheckin && okCheckout {
+			startDate, errStart := time.Parse("2006-01-02", checkinStr)
+			endDate, errEnd := time.Parse("2006-01-02", checkoutStr)
+
+			if errStart == nil && errEnd == nil {
+				duration := endDate.Sub(startDate).Hours() / 24
+				if duration > 14 {
+					fmt.Println("BLOCKED: Stay too long")
+					return map[string]any{"Error": "Maximum stay duration is 14 days."}, nil
+				}
+			}
+		}
+	}
+	return nil, nil
+}
+
+// Post-processing
+func afterToolCallback(ctx tool.Context, tool tool.Tool, args, result map[string]any, err error) (map[string]any, error) {
+	resultStr := fmt.Sprintf("%v", result)
+
+	if tool.Name() == "book-hotel" {
+		if !strings.Contains(resultStr, "Error") {
+			loyaltyBonus := 500
+			enrichedResult := fmt.Sprintf("Booking Confirmed!\n You earned %d Loyalty Points with this stay.\n\nSystem Details: %s", loyaltyBonus, resultStr)
+			return map[string]any{"confirmation": enrichedResult}, nil
+		}
+	}
+	return result, nil
+}
+
+func main() {
+	genaiKey := os.Getenv("GOOGLE_API_KEY")
+	toolboxURL := "http://localhost:5000"
+	ctx := context.Background()
+
+	toolboxClient, err := tbadk.NewToolboxClient(toolboxURL)
+	if err != nil {
+		log.Fatalf("Failed to create MCP Toolbox client: %v", err)
+	}
+
+	toolsetName := "my-toolset"
+	mcpTools, err := toolboxClient.LoadToolset(toolsetName, ctx)
+	if err != nil {
+		log.Fatalf("Failed to load MCP toolset '%s': %v\nMake sure your Toolbox server is running.", toolsetName, err)
+	}
+
+	model, err := gemini.NewModel(ctx, "gemini-2.5-flash", &genai.ClientConfig{
+		APIKey: genaiKey,
+	})
+	if err != nil {
+		log.Fatalf("Failed to create model: %v", err)
+	}
+
+	tools := make([]tool.Tool, len(mcpTools))
+	for i := range mcpTools {
+		tools[i] = &mcpTools[i]
+	}
+	llmagent, err := llmagent.New(llmagent.Config{
+		Name:                "hotel_assistant",
+		Model:               model,
+		Description:         "Agent to answer questions about hotels.",
+		Instruction:         systemPrompt,
+		Tools:               tools,
+		BeforeToolCallbacks: []llmagent.BeforeToolCallback{beforeToolCallback},
+		AfterToolCallbacks:  []llmagent.AfterToolCallback{afterToolCallback},
+	})
+	if err != nil {
+		log.Fatalf("Failed to create agent: %v", err)
+	}
+
+	appName := "hotel_assistant"
+	userID := "user-123"
+	sessionService := session.InMemoryService()
+	respSess, err := sessionService.Create(ctx, &session.CreateRequest{
+		AppName: appName,
+		UserID:  userID,
+	})
+	if err != nil {
+		log.Fatalf("Failed to create the session service: %v", err)
+	}
+	sess := respSess.Session
+
+	r, err := runner.New(runner.Config{
+		AppName:        appName,
+		Agent:          llmagent,
+		SessionService: sessionService,
+	})
+	if err != nil {
+		log.Fatalf("Failed to create runner: %v", err)
+	}
+
+	for i, query := range queries {
+		fmt.Printf("\n=== Query %d: %s ===\n", i+1, query)
+		userMsg := genai.NewContentFromText(query, genai.RoleUser)
+		streamingMode := agent.StreamingModeSSE
+
+		runIter := r.Run(ctx, userID, sess.ID(), userMsg, agent.RunConfig{
+			StreamingMode: streamingMode,
+		})
+
+		for event := range runIter {
+			if event != nil && event.LLMResponse.Content != nil {
+				for _, p := range event.LLMResponse.Content.Parts {
+					if streamingMode != agent.StreamingModeSSE || event.LLMResponse.Partial {
+						fmt.Print(p.Text)
+					}
+				}
+			}
+		}
+
+		fmt.Println("\n" + strings.Repeat("-", 80) + "\n")
+	}
+}