Files
MoviePilot/app/agent/middleware/tool_selection.py
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654 lines
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Python

"""MoviePilot 自定义工具筛选中间件。"""
from dataclasses import dataclass, replace
import json
from collections.abc import Awaitable, Callable
from typing import Annotated, Any, NotRequired
from langchain.agents.middleware.types import (
AgentState,
ContextT,
ModelRequest,
ModelResponse,
ResponseT,
)
from langchain.agents.middleware.types import (
PrivateStateAttr, # noqa
)
from langchain.agents.middleware.tool_selection import (
DEFAULT_SYSTEM_PROMPT,
LLMToolSelectorMiddleware,
)
from langchain_core.language_models.chat_models import BaseChatModel
from langchain_core.messages import AIMessage, HumanMessage, SystemMessage
from langchain_core.runnables import RunnableConfig
from langchain_core.tools import BaseTool
from langgraph.runtime import Runtime
from typing_extensions import TypedDict # noqa
from app.agent.llm import LLMHelper
from app.agent.tools.tags import ToolTag
from app.log import logger
MIN_SELECTED_TOOL_COUNT = 4
RECENT_SELECTION_CONTEXT_MESSAGE_LIMIT = 6
RECENT_SELECTION_CONTEXT_MAX_CHARS = 6000
RECENT_SELECTION_CONTEXT_TRUNCATION_PREFIX = "..."
TOOL_GROUP_EXCLUDED_TAGS = frozenset(
{
ToolTag.AgentTool.value,
ToolTag.Read.value,
ToolTag.Write.value,
ToolTag.Admin.value,
ToolTag.Message.value,
ToolTag.UserInteraction.value,
ToolTag.TerminalResponse.value,
}
)
MOVIEPILOT_TOOL_SELECTION_HINT = """
MoviePilot tool-chain hints:
- Tools with the same capability tag belong to the same functional group.
- For multi-step MoviePilot tasks, keep same-tag tools together when relevant.
- Prefer selecting likely next-step tools in the same capability group instead of selecting only the first tool.
"""
class ToolSelectionState(AgentState):
"""工具筛选中间件私有状态。"""
selected_tool_names: NotRequired[Annotated[list[str] | None, PrivateStateAttr]]
"""当前这条用户请求首轮筛选得到的工具名列表。"""
class ToolSelectionStateUpdate(TypedDict):
"""工具筛选中间件状态更新项。"""
selected_tool_names: list[str] | None
@dataclass(frozen=True)
class _ToolSelectionAttempt:
"""工具筛选尝试结果,用于统一记录最终日志。"""
request: ModelRequest
selected_tool_names: list[str]
status: str
detail: str = ""
class ToolSelectorMiddleware(LLMToolSelectorMiddleware):
"""
使用 provider-neutral JSON 提示执行工具筛选。
LangChain 默认会通过 `with_structured_output()` 走 provider-specific 的
结构化输出能力,不同 OpenAI/Anthropic 兼容端点对 `response_format`、
JSON schema 和工具绑定的支持并不一致。工具筛选只是 Agent 执行前的
辅助优化,失败时也会恢复使用全部工具,因此这里统一使用文本提示约束
模型返回 `{"tools": [...]}` 并手动解析,避免在筛选阶段引入额外兼容分支。
另外,LangChain 原生工具筛选挂在 `wrap_model_call` 上,会在同一条用户请求
的每次“模型回合”前都重新筛选一次工具。对于会多轮调用工具的复杂任务,
这会重复消耗一次额外的 LLM 调用。这里改成:
- `abefore_agent()`:在本轮 Agent 执行开始时筛选一次;
- `awrap_model_call()`:从 `request.state` 读取首轮筛选结果并复用。
"""
state_schema = ToolSelectionState
def __init__(
self,
model: BaseChatModel | str | None = None,
system_prompt: str = DEFAULT_SYSTEM_PROMPT,
selection_tools: list[Any] | None = None,
max_tools: int | None = None,
always_include: list[str] | None = None,
) -> None:
super().__init__(
model=model,
system_prompt=self._append_tool_selection_hint(system_prompt),
max_tools=max_tools,
always_include=always_include,
)
self.selection_tools = selection_tools or []
@classmethod
def _render_recent_conversation_context(
cls,
messages: list[Any],
) -> tuple[str, int]:
"""渲染最近对话上下文,供工具筛选模型理解多轮追问。"""
rendered_messages = []
for message in messages:
if isinstance(message, HumanMessage):
role = "User"
elif isinstance(message, AIMessage):
role = "Assistant"
else:
continue
content = LLMHelper.extract_text_content(message.content).strip()
if not content:
continue
rendered_messages.append(f"{role}: {content}")
recent_messages = rendered_messages[-RECENT_SELECTION_CONTEXT_MESSAGE_LIMIT:]
context = "\n\n".join(recent_messages)
if len(context) > RECENT_SELECTION_CONTEXT_MAX_CHARS:
context = (
f"{RECENT_SELECTION_CONTEXT_TRUNCATION_PREFIX}"
f"{context[-RECENT_SELECTION_CONTEXT_MAX_CHARS:]}"
)
return context, len(recent_messages)
@classmethod
def _build_contextual_user_message(
cls,
messages: list[Any],
last_user_message: HumanMessage,
) -> HumanMessage:
"""根据最近对话构造工具筛选专用用户消息。"""
context, message_count = cls._render_recent_conversation_context(messages)
if message_count <= 1:
return last_user_message
return HumanMessage(
content=(
"Recent conversation context for tool selection:\n"
f"{context}\n\n"
"Select tools for the latest user instruction. Use prior assistant "
"messages and earlier user requests when the latest user message "
"depends on previous context."
)
)
def _prepare_selection_request(
self,
request: ModelRequest[ContextT],
) -> Any | None:
"""准备带最近对话上下文的工具筛选请求。"""
selection_request = super()._prepare_selection_request(request)
if selection_request is None:
return None
contextual_user_message = self._build_contextual_user_message(
messages=request.messages,
last_user_message=selection_request.last_user_message,
)
if contextual_user_message is selection_request.last_user_message:
return selection_request
return replace(selection_request, last_user_message=contextual_user_message)
@staticmethod
def _append_tool_selection_hint(system_prompt: str) -> str:
"""追加 MoviePilot 工具组选择提示,避免复杂链路只选中首个工具。"""
if "MoviePilot tool-chain hints:" in system_prompt:
return system_prompt
return f"{system_prompt.rstrip()}{MOVIEPILOT_TOOL_SELECTION_HINT}"
def _get_tool_selection_limit(self, valid_tool_names: list[str]) -> int:
"""计算补齐筛选结果时允许使用的工具数量上限。"""
if self.max_tools:
return min(self.max_tools, len(valid_tool_names))
return len(valid_tool_names)
@staticmethod
def _normalize_tool_tags(tool: BaseTool) -> list[str]:
"""读取工具的业务标签,过滤掉无法表达工具组的通用标签。"""
tags = getattr(tool, "tags", None) or []
if isinstance(tags, str):
tags = [tags]
normalized_tags = []
for tag in tags:
tag_value = getattr(tag, "value", tag)
if not tag_value:
continue
tag_name = str(tag_value)
if tag_name in TOOL_GROUP_EXCLUDED_TAGS or tag_name in normalized_tags:
continue
normalized_tags.append(tag_name)
return normalized_tags
@classmethod
def _build_tool_groups(
cls,
available_tools: list[BaseTool],
valid_tool_names: list[str],
) -> list[tuple[str, list[str]]]:
"""根据工具标签构造能力组,保留当前工具列表中的稳定顺序。"""
valid_tool_set = set(valid_tool_names)
tool_groups: dict[str, list[str]] = {}
for tool in available_tools:
tool_name = getattr(tool, "name", None)
if not tool_name or tool_name not in valid_tool_set:
continue
for tag in cls._normalize_tool_tags(tool):
group_tool_names = tool_groups.setdefault(tag, [])
if tool_name not in group_tool_names:
group_tool_names.append(tool_name)
return [
(tag, tool_names)
for tag, tool_names in tool_groups.items()
if len(tool_names) > 1
]
@classmethod
def _get_matched_tool_groups(
cls,
selected_names: list[str],
available_tools: list[BaseTool],
valid_tool_names: list[str],
) -> list[tuple[str, list[str]]]:
"""返回已选工具命中的标签能力组。"""
groups_by_tag = {
tag: tool_names
for tag, tool_names in cls._build_tool_groups(
available_tools=available_tools,
valid_tool_names=valid_tool_names,
)
}
tools_by_name = {
tool.name: tool
for tool in available_tools
if getattr(tool, "name", None)
}
matched_groups: list[tuple[str, list[str]]] = []
seen_tags = set()
for tool_name in selected_names:
tool = tools_by_name.get(tool_name)
if not tool:
continue
for tag in cls._normalize_tool_tags(tool):
if tag in seen_tags or tag not in groups_by_tag:
continue
matched_groups.append((tag, groups_by_tag[tag]))
seen_tags.add(tag)
return matched_groups
def _complete_low_count_selection(
self,
selected_tool_names: list[str],
valid_tool_names: list[str],
available_tools: list[BaseTool],
) -> list[str]:
"""
当模型只选出极少工具时,按工具标签补齐同组工具。
工具标签是工具自身声明的能力归属。这里只补齐已经命中的标签组,
不会把所有工具组都展开。
"""
limit = self._get_tool_selection_limit(valid_tool_names)
selected_names = [
tool_name
for tool_name in selected_tool_names
if tool_name in valid_tool_names
]
selected_set = set(selected_names)
valid_tool_set = set(valid_tool_names)
completed_names = list(selected_names)
matched_groups = self._get_matched_tool_groups(
selected_names=selected_names,
available_tools=available_tools,
valid_tool_names=valid_tool_names,
)
if not matched_groups:
return completed_names[:limit]
matched_group_tool_names = {
tool_name
for _, group_tool_names in matched_groups
for tool_name in group_tool_names
}
target_count = min(
max(MIN_SELECTED_TOOL_COUNT, len(matched_group_tool_names)),
limit,
)
if len(selected_names) >= target_count:
return selected_names[:limit]
for _, group_tool_names in matched_groups:
for tool_name in group_tool_names:
if tool_name in selected_set or tool_name not in valid_tool_set:
continue
completed_names.append(tool_name)
selected_set.add(tool_name)
if len(completed_names) >= target_count:
return completed_names[:limit]
return completed_names[:limit]
def _process_selection_response(
self,
response: dict[str, Any],
available_tools: list[BaseTool],
valid_tool_names: list[str],
request: ModelRequest[ContextT],
) -> ModelRequest[ContextT]:
"""
处理工具筛选响应,并在正常空结果时禁用可筛选工具。
"""
if response.get("tools") == []:
always_included_tools: list[BaseTool] = [
tool
for tool in request.tools
if not isinstance(tool, dict) and tool.name in self.always_include
]
provider_tools = [tool for tool in request.tools if isinstance(tool, dict)]
return request.override(tools=[*always_included_tools, *provider_tools])
response["tools"] = self._complete_low_count_selection(
selected_tool_names=[
tool_name
for tool_name in response.get("tools", [])
if isinstance(tool_name, str)
],
valid_tool_names=valid_tool_names,
available_tools=available_tools,
)
modified_request = super()._process_selection_response(
response,
available_tools,
valid_tool_names,
request,
)
return modified_request
@staticmethod
def _parse_json_object(text: str) -> dict[str, Any]:
"""
解析模型返回的 JSON。
不同模型可能偶发输出 Markdown 围栏或前后说明文本,因此这里从
响应中提取第一个 JSON 对象作为兜底。
"""
stripped_text = text.strip()
if not stripped_text:
raise ValueError("工具筛选返回了空响应")
try:
payload = json.loads(stripped_text)
if isinstance(payload, dict):
return payload
except json.JSONDecodeError:
pass
start = stripped_text.find("{")
end = stripped_text.rfind("}")
if start == -1 or end == -1 or end <= start:
raise ValueError(f"工具筛选返回的内容不是合法 JSON: {stripped_text}")
payload = json.loads(stripped_text[start: end + 1])
if not isinstance(payload, dict):
raise ValueError("工具筛选 JSON 顶层必须是对象")
return payload
@classmethod
def _render_tool_list(cls, available_tools: list[Any]) -> str:
"""把工具名和描述渲染成稳定的文本列表。"""
lines = []
for tool in available_tools:
tags = cls._normalize_tool_tags(tool)
tag_text = f" [group tags: {', '.join(tags)}]" if tags else ""
lines.append(f"- {tool.name}{tag_text}: {tool.description}")
return "\n".join(lines)
@classmethod
def _render_tool_groups(cls, available_tools: list[BaseTool]) -> str:
"""把当前可用工具按标签渲染成能力组提示。"""
valid_tool_names = [
tool.name
for tool in available_tools
if getattr(tool, "name", None)
]
groups = cls._build_tool_groups(
available_tools=available_tools,
valid_tool_names=valid_tool_names,
)
if not groups:
return ""
rendered_groups = "\n".join(
f"- {tag}: {', '.join(tool_names)}"
for tag, tool_names in groups
)
return f"Capability groups from tool tags:\n{rendered_groups}\n\n"
def _build_json_selection_prompt(self, selection_request: Any) -> str:
"""
生成显式 JSON 输出提示。
使用纯提示约束可覆盖更多兼容端点,避免在工具筛选阶段依赖某个
provider 专属的 `response_format` 或 schema 能力。
"""
limit_instruction = ""
if self.max_tools:
limit_instruction = f"- Select up to {self.max_tools} tools. Return an empty array if no tools are relevant."
return (
f"{selection_request.system_message}\n\n"
"Return the answer in JSON only.\n"
'Use exactly this shape: {"tools": ["tool_name_1", "tool_name_2"]}\n'
"Rules:\n"
"- The `tools` field must be a JSON array of strings.\n"
"- Only use tool names from the allowed list below.\n"
"- Order tools by relevance, with the most relevant first.\n"
"- Tools sharing the same capability tag are in the same group; include same-group tools together when relevant.\n"
f"{limit_instruction}\n"
"- Do not add explanations, markdown, or extra keys.\n\n"
f"{self._render_tool_groups(selection_request.available_tools)}"
"Allowed tools:\n"
f"{self._render_tool_list(selection_request.available_tools)}"
)
def _normalize_selection_response(self, response: Any) -> dict[str, list[str]]:
"""
解析并标准化显式 JSON 模式的工具筛选结果。
"""
content = getattr(response, "content", response)
text = LLMHelper.extract_text_content(content)
logger.debug(f"工具筛选原始响应: {text}")
payload = self._parse_json_object(text)
tools = payload.get("tools")
if not isinstance(tools, list):
raise ValueError(f"工具筛选 JSON 缺少 `tools` 数组: {payload}")
normalized_tools = [
tool_name for tool_name in tools if isinstance(tool_name, str)
]
logger.debug(f"工具筛选标准化结果: {normalized_tools}")
return {"tools": normalized_tools}
async def _aselect_tools_with_json_prompt(
self, selection_request: Any
) -> dict[str, list[str]]:
"""
使用 JSON 提示执行异步工具筛选。
:param selection_request: LangChain 工具筛选请求
:return: 标准化后的工具名列表
"""
logger.debug("工具筛选走 JSON 提示分支")
response = await selection_request.model.ainvoke(
[
SystemMessage(
content=self._build_json_selection_prompt(selection_request)
),
selection_request.last_user_message,
]
)
return self._normalize_selection_response(response)
@staticmethod
def _extract_selected_tool_names(request: ModelRequest) -> list[str]:
"""从已筛选后的请求中提取最终工具名,保留原有顺序。"""
return [tool.name for tool in request.tools if not isinstance(tool, dict)]
@staticmethod
def _count_request_tools(request: ModelRequest) -> int:
"""统计当前请求中的 LangChain 工具数量,不包含 provider 原生工具字典。"""
return len([tool for tool in request.tools if not isinstance(tool, dict)])
@classmethod
def _log_selection_attempt(cls, attempt: _ToolSelectionAttempt) -> None:
"""按工具筛选最终状态记录稳定日志。"""
tool_count = cls._count_request_tools(attempt.request)
if attempt.status == "selected":
selected_text = ", ".join(attempt.selected_tool_names) or "无有效工具"
logger.info(f"工具筛选结果: {selected_text}")
return
if attempt.status == "failed_fallback":
logger.warning(
f"工具筛选失败,将恢复使用所有工具(共 {tool_count} 个): {attempt.detail}"
)
return
if attempt.status == "skipped":
logger.info(f"工具筛选跳过: {attempt.detail}。")
return
if attempt.status == "reused":
selected_text = ", ".join(attempt.selected_tool_names) or "无有效工具"
logger.info(f"工具筛选复用已有结果: {selected_text}")
@staticmethod
def _apply_selected_tools(
request: ModelRequest[ContextT],
selected_tool_names: list[str],
) -> ModelRequest[ContextT]:
"""
将已筛选出的工具集应用到当前模型请求。
这里只复用首次筛选出的客户端工具名;provider-specific 的 dict 工具仍然
原样保留,避免破坏 LangChain/provider 自身的工具绑定约定。
"""
current_tools_by_name = {
tool.name: tool for tool in request.tools if not isinstance(tool, dict)
}
selected_tools = [
current_tools_by_name[tool_name]
for tool_name in selected_tool_names
if tool_name in current_tools_by_name
]
provider_tools = [tool for tool in request.tools if isinstance(tool, dict)]
return request.override(tools=[*selected_tools, *provider_tools])
async def _aselect_request_once(
self, request: ModelRequest[ContextT]
) -> ModelRequest[ContextT]:
"""
执行一次真实工具筛选,并返回筛选后的请求对象。
这里单独抽成 helper,便于首次筛选后缓存结果,也便于测试覆盖
“首轮筛选,后续复用”的行为。
"""
return (await self._aselect_request_once_with_status(request)).request
async def _aselect_request_once_with_status(
self, request: ModelRequest[ContextT]
) -> _ToolSelectionAttempt:
"""
执行一次真实工具筛选,并携带最终状态供调用方统一记录日志。
"""
selection_request = self._prepare_selection_request(request)
if selection_request is None:
return _ToolSelectionAttempt(
request=request,
selected_tool_names=self._extract_selected_tool_names(request),
status="skipped",
detail="没有需要筛选的工具",
)
try:
response = await self._aselect_tools_with_json_prompt(selection_request)
modified_request = self._process_selection_response(
response,
selection_request.available_tools,
selection_request.valid_tool_names,
request,
)
return _ToolSelectionAttempt(
request=modified_request,
selected_tool_names=self._extract_selected_tool_names(modified_request),
status="selected",
)
except Exception as err:
return _ToolSelectionAttempt(
request=request,
selected_tool_names=self._extract_selected_tool_names(request),
status="failed_fallback",
detail=str(err),
)
async def abefore_agent( # noqa
self,
state: ToolSelectionState,
runtime: Runtime, # noqa
config: RunnableConfig,
) -> ToolSelectionStateUpdate | None: # ty: ignore[invalid-method-override]
"""
在本轮 Agent 执行开始前完成一次真实工具筛选。
这样后续多轮 `model -> tools -> model` 循环都只复用这一次结果,
不会为每次模型回合重复追加一笔 selector LLM 开销。
"""
if not self.selection_tools or self.model is None:
detail = "没有可筛选工具" if not self.selection_tools else "未配置筛选模型"
self._log_selection_attempt(
_ToolSelectionAttempt(
request=ModelRequest(
model=self.model,
tools=list(self.selection_tools),
messages=state["messages"],
state=state,
runtime=runtime,
),
selected_tool_names=[],
status="skipped",
detail=detail,
)
)
return ToolSelectionStateUpdate(selected_tool_names=None)
selection_request = ModelRequest(
model=self.model,
tools=list(self.selection_tools),
messages=state["messages"],
state=state,
runtime=runtime,
)
attempt = await self._aselect_request_once_with_status(selection_request)
self._log_selection_attempt(attempt)
selected_tool_names = attempt.selected_tool_names
return ToolSelectionStateUpdate(selected_tool_names=selected_tool_names)
async def awrap_model_call(
self,
request: ModelRequest[ContextT],
handler: Callable[
[ModelRequest[ContextT]], Awaitable[ModelResponse[ResponseT]]
],
) -> ModelResponse[ResponseT]:
"""
从 state 中读取首次筛选结果,并应用到每次模型回合。
"""
selected_tool_names = request.state.get("selected_tool_names") # noqa
# 正常路径下,`abefore_agent()` 已经提前写入状态;这里只保留一层兜底,
# 兼容直接单测或未来某些绕过 before_agent 的调用场景。
if (
selected_tool_names is None
and self.selection_tools
and self.model is not None
):
attempt = await self._aselect_request_once_with_status(request)
self._log_selection_attempt(attempt)
request = attempt.request
selected_tool_names = attempt.selected_tool_names
request.state["selected_tool_names"] = selected_tool_names # noqa
if selected_tool_names is not None:
request = self._apply_selected_tools(request, selected_tool_names)
return await handler(request)