add adk samples

docs/en/samples/pre_post_processing/python/adk/agent.py

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+# 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.
+
+import asyncio
+from datetime import datetime
+from typing import Any, Dict, Optional, Awaitable
+
+from google.adk import Agent
+from google.adk.apps import App
+from google.adk.agents import InvocationContext
+from toolbox_adk import ToolboxToolset, CredentialStrategy
+
+system_prompt = """
+  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.
+"""
+
+async def before_tool_callback(context: Any, args: Dict[str, Any]):
+    """
+    Callback fired before a tool is executed.
+    Enforces business logic: Max stay duration is 14 days.
+    """
+    tool_name = getattr(context, "name", "unknown_tool")
+    
+    print(f"POLICY CHECK: Intercepting '{tool_name}'")
+    if tool_name == "update-hotel" or ("checkin_date" in args and "checkout_date" in args):
+        try:
+            start = datetime.fromisoformat(args["checkin_date"])
+            end = datetime.fromisoformat(args["checkout_date"])
+            duration = (end - start).days
+
+            if duration > 14:
+                print("BLOCKED: Stay too long")
+                raise ValueError("Error: Maximum stay duration is 14 days.")
+        except ValueError as e:
+            if "Maximum stay duration" in str(e):
+                raise
+            pass 
+            
+    return args
+
+async def after_tool_callback(context: Any, args: Dict[str, Any], result: Any, error: Optional[Exception]) -> Awaitable[Any]:
+    """
+    Callback fired after a tool execution.
+    Enriches response for successful bookings.
+    """
+    tool_name = getattr(context, "name", "unknown_tool")
+
+    if error:
+        print(f"[Tool-Level] after_tool_callback: Tool '{tool_name}' failed with error: {error}")
+        return None
+    if isinstance(result, str) and "Error" not in result:
+        is_booking = tool_name == "book-hotel" or "booking" in str(result).lower() or "confirmed" in str(result).lower()
+        
+        if is_booking:
+             loyalty_bonus = 500
+             return f"Booking Confirmed!\n You earned {loyalty_bonus} Loyalty Points with this stay.\n\nSystem Details: {result}"
+    return result
+
+async def main():
+    print("🚀 Initializing ADK Agent with Toolbox...")
+
+    toolset = ToolboxToolset(
+        server_url="http://127.0.0.1:5000",
+        toolset_name="my-toolset",
+        credentials=CredentialStrategy.toolbox_identity(),
+        pre_hook=before_tool_callback,
+        post_hook=after_tool_callback
+    )
+
+    root_agent = Agent(
+        name='root_agent',
+        model='gemini-2.5-flash',
+        instruction=system_prompt,
+        tools=[toolset],
+    )
+
+    app = App(root_agent=root_agent, name="my_agent")
+    user_input = "Book hotel with id 3."
+    print(f"\nUSER: '{user_input}'")
+    
+    # Note: run_async expects an InvocationContext and returns an async generator
+    context = InvocationContext(text=user_input)
+    response_text = ""
+    async for chunk in root_agent.run_async(context):
+        # Accumulate text from chunks
+        text_chunk = getattr(chunk, 'text', str(chunk))
+        if text_chunk:
+             response_text += text_chunk
+
+    print(f"AI: {response_text}")
+    
+    # Test Pre-processing
+    print("-" * 50)
+    user_input_2 = "Update my hotel with id 3 with checkin date 2025-01-18 and checkout date 2025-02-10" # > 14 days
+    print(f"USER: '{user_input_2}'")
+    
+    context_2 = InvocationContext(text=user_input_2)
+    response_text = ""
+    async for chunk in root_agent.run_async(context_2):
+        text_chunk = getattr(chunk, 'text', str(chunk))
+        if text_chunk:
+             response_text += text_chunk
+             
+    print(f"AI: {response_text}")
+
+if __name__ == "__main__":
+    asyncio.run(main())

docs/en/samples/pre_post_processing/python/adk/requirements.txt

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+google-adk[toolbox]==1.23.0
+pytest==9.0.2