chore: import upstream snapshot with attribution

python/semantic_kernel/agents/strategies/selection/selection_strategy.py

@@ -0,0 +1,57 @@
+# Copyright (c) Microsoft. All rights reserved.
+
+from abc import ABC
+from typing import TYPE_CHECKING
+
+from semantic_kernel.agents import Agent
+from semantic_kernel.exceptions.agent_exceptions import AgentExecutionException
+from semantic_kernel.kernel_pydantic import KernelBaseModel
+from semantic_kernel.utils.feature_stage_decorator import experimental
+
+if TYPE_CHECKING:
+    from semantic_kernel.contents.chat_message_content import ChatMessageContent
+
+
+@experimental
+class SelectionStrategy(KernelBaseModel, ABC):
+    """Base strategy class for selecting the next agent in a chat."""
+
+    has_selected: bool = False
+    initial_agent: Agent | None = None
+
+    async def next(
+        self,
+        agents: list[Agent],
+        history: list["ChatMessageContent"],
+    ) -> Agent:
+        """Select the next agent to interact with.
+
+        Args:
+            agents: The list of agents to select from.
+            history: The history of messages in the conversation.
+
+        Returns:
+            The agent who takes the next turn.
+        """
+        if not agents and self.initial_agent is None:
+            raise AgentExecutionException("Agent Failure - No agents present to select.")
+
+        # If it's the first selection and we have an initial agent, use it
+        if not self.has_selected and self.initial_agent is not None:
+            agent = self.initial_agent
+        else:
+            agent = await self.select_agent(agents, history)
+
+        self.has_selected = True
+        return agent
+
+    async def select_agent(
+        self,
+        agents: list[Agent],
+        history: list["ChatMessageContent"],
+    ) -> Agent:
+        """Determines which agent goes next. Override for custom logic.
+
+        By default, this fallback returns the first agent in the list.
+        """
+        return agents[0]