def _build_base_graph():
    """Build and return the base state graph with all nodes and edges."""
    builder = StateGraph(State)
    builder.add_edge(START, "coordinator")
    builder.add_node("coordinator", coordinator_node)
    builder.add_node("background_investigator", background_investigation_node)
    builder.add_node("planner", planner_node)
    builder.add_node("reporter", reporter_node)
    builder.add_node("research_team", research_team_node)
    builder.add_node("researcher", researcher_node)
    builder.add_node("coder", coder_node)
    builder.add_node("human_feedback", human_feedback_node)
    builder.add_edge("background_investigator", "planner")
    builder.add_conditional_edges(
        "research_team",
        continue_to_running_research_team,
        ["planner", "researcher", "coder"],
    )
    builder.add_edge("reporter", END)
    return builder

def coordinator_node(
    state: State, config: RunnableConfig
) -> Command[Literal["planner", "background_investigator", "__end__"]]:
    """Coordinator node that communicate with customers."""
    logger.info("Coordinator talking.")
    configurable = Configuration.from_runnable_config(config)
    messages = apply_prompt_template("coordinator", state) # prompt就是coordinator.md。里面指示了 llm需要做什么，对每种情况如何回复，什么时候需要分发请求。
    response = (
        get_llm_by_type(AGENT_LLM_MAP["coordinator"])
        .bind_tools([handoff_to_planner])
        .invoke(messages)
    ) # 初始化 llm 客户端 并调用llm
    # 这里prompt指定多数情况都调用handoff_to_planner，
    logger.debug(f"Current state messages: {state['messages']}")

    goto = "__end__"
    locale = state.get("locale", "en-US")  # Default locale if not specified
    research_topic = state.get("research_topic", "")

    if len(response.tool_calls) > 0: # 检查大模型想不想要调用工具
        goto = "planner"
        if state.get("enable_background_investigation"):
            # if the search_before_planning is True, add the web search tool to the planner agent
            goto = "background_investigator"
        try:
            for tool_call in response.tool_calls:
                if tool_call.get("name", "") != "handoff_to_planner":
                    continue
                if tool_call.get("args", {}).get("locale") and tool_call.get(
                    "args", {}
                ).get("research_topic"): 
                # 如果大模型调用工具，它会返回要调用的工具名，也就是 handoff_to_planner，还有这个函数的参数 research_topic 就是我们输入的提问
                    locale = tool_call.get("args", {}).get("locale")
                    research_topic = tool_call.get("args", {}).get("research_topic")
                    break
        except Exception as e:
            logger.error(f"Error processing tool calls: {e}")
    else:
        logger.warning(
            "Coordinator response contains no tool calls. Terminating workflow execution."
        )
        logger.debug(f"Coordinator response: {response}")
    messages = state.get("messages", [])

    # 调用函数的情况下没有 content，返回一个command，第一次进来 goto=background_investigator
    if response.content:
        messages.append(HumanMessage(content=response.content, name="coordinator"))
    return Command(
        update={
            "messages": messages,
            "locale": locale,
            "research_topic": research_topic,
            "resources": configurable.resources,
        },
        goto=goto,
    )

def background_investigation_node(state: State, config: RunnableConfig):
    logger.info("background investigation node is running.")
    configurable = Configuration.from_runnable_config(config)
    query = state.get("research_topic")
    background_investigation_results = None
    if SELECTED_SEARCH_ENGINE == SearchEngine.TAVILY.value:
        searched_content = LoggedTavilySearch(
            max_results=configurable.max_search_results
        ).invoke(query)
        if isinstance(searched_content, list):
            # 把TAVILY的搜索结果拼起来，然后就返回
            background_investigation_results = [
                f"## {elem['title']}\n\n{elem['content']}" for elem in searched_content
            ]
            return {
                "background_investigation_results": "\n\n".join(
                    background_investigation_results
                )
            }
        else:
            logger.error(
                f"Tavily search returned malformed response: {searched_content}"
            )
    else:
        background_investigation_results = get_web_search_tool(
            configurable.max_search_results
        ).invoke(query)
    return {
        "background_investigation_results": json.dumps(
            background_investigation_results, ensure_ascii=False
        )
    }

builder.add_edge("background_investigator", "planner")

def planner_node(
    state: State, config: RunnableConfig
) -> Command[Literal["human_feedback", "reporter"]]:
    """Planner node that generate the full plan."""
    logger.info("Planner generating full plan")
    configurable = Configuration.from_runnable_config(config)
    plan_iterations = state["plan_iterations"] if state.get("plan_iterations", 0) else 0
    messages = apply_prompt_template("planner", state, configurable)

    if state.get("enable_background_investigation") and state.get(
        "background_investigation_results"
    ):
        # background_investigation_results 是上一步查询的初始结果
        messages += [
            {
                "role": "user",
                "content": (
                    "background investigation results of user query:\n"
                    + state["background_investigation_results"]
                    + "\n"
                ),
            }
        ]

    if configurable.enable_deep_thinking:
        llm = get_llm_by_type("reasoning")
    elif AGENT_LLM_MAP["planner"] == "basic": # 进入这里
        llm = get_llm_by_type("basic").with_structured_output(
            Plan,
            # method="json_mode",
        )
    else:
        llm = get_llm_by_type(AGENT_LLM_MAP["planner"])

    # if the plan iterations is greater than the max plan iterations, return the reporter node
    if plan_iterations >= configurable.max_plan_iterations:
        return Command(goto="reporter")

    full_response = ""
    if AGENT_LLM_MAP["planner"] == "basic" and not configurable.enable_deep_thinking:
        response = llm.invoke(messages)
        full_response = response.model_dump_json(indent=4, exclude_none=True)
    else:
        response = llm.stream(messages)
        for chunk in response:
            full_response += chunk.content
    logger.debug(f"Current state messages: {state['messages']}")
    logger.info(f"Planner response: {full_response}")
    # response的结果取决于plan的prompt，llm会thought然后列出他要做的每一个step

    try:
        curr_plan = json.loads(repair_json_output(full_response))
    except json.JSONDecodeError:
        logger.warning("Planner response is not a valid JSON")
        if plan_iterations > 0:
            return Command(goto="reporter")
        else:
            return Command(goto="__end__")
    if isinstance(curr_plan, dict) and curr_plan.get("has_enough_context"): # llm觉得够了的情况
        logger.info("Planner response has enough context.")
        new_plan = Plan.model_validate(curr_plan)
        return Command(
            update={
                "messages": [AIMessage(content=full_response, name="planner")],
                "current_plan": new_plan,
            },
            goto="reporter",
        )
    # 否则需要继续查
    return Command(
        update={
            "messages": [AIMessage(content=full_response, name="planner")],
            "current_plan": full_response,
        },
        goto="human_feedback",
    )

def human_feedback_node(
    state,
) -> Command[Literal["planner", "research_team", "reporter", "__end__"]]:
    current_plan = state.get("current_plan", "")
    # check if the plan is auto accepted
    auto_accepted_plan = state.get("auto_accepted_plan", False)
    if not auto_accepted_plan: # auto_accepted_plan 表示是否自动，如果不是自动，就需要人类反馈，我这里是 true，
        feedback = interrupt("Please Review the Plan.")

        # if the feedback is not accepted, return the planner node
        if feedback and str(feedback).upper().startswith("[EDIT_PLAN]"):
            return Command(
                update={
                    "messages": [
                        HumanMessage(content=feedback, name="feedback"),
                    ],
                },
                goto="planner",
            )
        elif feedback and str(feedback).upper().startswith("[ACCEPTED]"):
            logger.info("Plan is accepted by user.")
        else:
            raise TypeError(f"Interrupt value of {feedback} is not supported.")

    # if the plan is accepted, run the following node
    plan_iterations = state["plan_iterations"] if state.get("plan_iterations", 0) else 0
    goto = "research_team"
    try:
        current_plan = repair_json_output(current_plan)
        # increment the plan iterations
        plan_iterations += 1
        # parse the plan
        new_plan = json.loads(current_plan)
    except json.JSONDecodeError:
        logger.warning("Planner response is not a valid JSON")
        if plan_iterations > 1:  # the plan_iterations is increased before this check
            return Command(goto="reporter")
        else:
            return Command(goto="__end__")

    return Command(
        update={
            "current_plan": Plan.model_validate(new_plan), # 把json转成类对象
            "plan_iterations": plan_iterations,
            "locale": new_plan["locale"],
        },
        goto=goto,
    )

def research_team_node(state: State):
    """Research team node that collaborates on tasks."""
    logger.info("Research team is collaborating on tasks.")
    pass

builder.add_conditional_edges(
        "research_team",
        continue_to_running_research_team,
        ["planner", "researcher", "coder"],
    )
def continue_to_running_research_team(state: State):
    current_plan = state.get("current_plan") # current_plan 就是上一步生成的plan
    if not current_plan or not current_plan.steps:
        return "planner"

    if all(step.execution_res for step in current_plan.steps): # 所有plan都有结果了
        return "planner"

    # Find first incomplete step
    incomplete_step = None
    for step in current_plan.steps:
        if not step.execution_res:
            incomplete_step = step
            break

    if not incomplete_step:
        return "planner"

    # step_type也是上一步planner生成的
    if incomplete_step.step_type == StepType.RESEARCH:
        return "researcher"
    if incomplete_step.step_type == StepType.PROCESSING:
        return "coder"
    return "planner"

async def researcher_node(
    state: State, config: RunnableConfig
) -> Command[Literal["research_team"]]:
    """Researcher node that do research"""
    logger.info("Researcher node is researching.")
    configurable = Configuration.from_runnable_config(config)
    tools = [get_web_search_tool(configurable.max_search_results), crawl_tool]
    retriever_tool = get_retriever_tool(state.get("resources", []))
    if retriever_tool:
        tools.insert(0, retriever_tool)
    logger.info(f"Researcher tools: {tools}")
    return await _setup_and_execute_agent_step(
        state,
        config,
        "researcher",
        tools,
    )

if mcp_servers:
   ...
else:
    # Use default tools if no MCP servers are configured
    agent = create_agent(agent_type, agent_type, default_tools, agent_type)
    return await _execute_agent_step(state, agent, agent_type)

async def _execute_agent_step(
    state: State, agent, agent_name: str
) -> Command[Literal["research_team"]]:
    """Helper function to execute a step using the specified agent."""
    current_plan = state.get("current_plan")
    plan_title = current_plan.title
    observations = state.get("observations", [])

    # Find the first unexecuted step
    current_step = None
    completed_steps = []
    for step in current_plan.steps:
        if not step.execution_res:
            current_step = step
            break
        else:
            completed_steps.append(step)

    if not current_step:
        logger.warning("No unexecuted step found")
        return Command(goto="research_team")

    logger.info(f"Executing step: {current_step.title}, agent: {agent_name}")

    # Format completed steps information
    completed_steps_info = ""
    if completed_steps:
        completed_steps_info = "# Completed Research Steps\n\n"
        for i, step in enumerate(completed_steps):
            completed_steps_info += f"## Completed Step {i + 1}: {step.title}\n\n"
            completed_steps_info += f"<finding>\n{step.execution_res}\n</finding>\n\n"

    # Prepare the input for the agent with completed steps info
    agent_input = {
        "messages": [
            HumanMessage(
                content=f"# Research Topic\n\n{plan_title}\n\n{completed_steps_info}# Current Step\n\n## Title\n\n{current_step.title}\n\n## Description\n\n{current_step.description}\n\n## Locale\n\n{state.get('locale', 'en-US')}"
            )
        ]
    }

    # Add citation reminder for researcher agent
    if agent_name == "researcher":
        if state.get("resources"):
            resources_info = "**The user mentioned the following resource files:**\n\n"
            for resource in state.get("resources"):
                resources_info += f"- {resource.title} ({resource.description})\n"

            agent_input["messages"].append(
                HumanMessage(
                    content=resources_info
                    + "\n\n"
                    + "You MUST use the **local_search_tool** to retrieve the information from the resource files.",
                )
            )

        agent_input["messages"].append(
            HumanMessage(
                content="IMPORTANT: DO NOT include inline citations in the text. Instead, track all sources and include a References section at the end using link reference format. Include an empty line between each citation for better readability. Use this format for each reference:\n- [Source Title](URL)\n\n- [Another Source](URL)",
                name="system",
            )
        )

    # Invoke the agent
    default_recursion_limit = 25
    try:
        env_value_str = os.getenv("AGENT_RECURSION_LIMIT", str(default_recursion_limit))
        parsed_limit = int(env_value_str)

        if parsed_limit > 0:
            recursion_limit = parsed_limit
            logger.info(f"Recursion limit set to: {recursion_limit}")
        else:
            logger.warning(
                f"AGENT_RECURSION_LIMIT value '{env_value_str}' (parsed as {parsed_limit}) is not positive. "
                f"Using default value {default_recursion_limit}."
            )
            recursion_limit = default_recursion_limit
    except ValueError:
        raw_env_value = os.getenv("AGENT_RECURSION_LIMIT")
        logger.warning(
            f"Invalid AGENT_RECURSION_LIMIT value: '{raw_env_value}'. "
            f"Using default value {default_recursion_limit}."
        )
        recursion_limit = default_recursion_limit

    logger.info(f"Agent input: {agent_input}")
    # ainvoke函数：Agent 框架会自动处理 LLM 的输出，解析是否需要调用工具，并自动执行工具调用循环
    result = await agent.ainvoke(
        input=agent_input, config={"recursion_limit": recursion_limit}
    )

    logger.info(f"research_result:{result}")
    # Process the result
    response_content = result["messages"][-1].content
    logger.debug(f"{agent_name.capitalize()} full response: {response_content}")

    # Update the step with the execution result
    current_step.execution_res = response_content
    logger.info(f"Step '{current_step.title}' execution completed by {agent_name}")

    return Command(
        update={
            "messages": [
                HumanMessage(
                    content=response_content,
                    name=agent_name,
                )
            ],
            "observations": observations + [response_content],
        },
        goto="research_team",
    )

def continue_to_running_research_team(state: State):
    current_plan = state.get("current_plan") # current_plan 是planner生成的
    if not current_plan or not current_plan.steps:
        return "planner"

    if all(step.execution_res for step in current_plan.steps): # 所有plan都有结果了
        return "planner"

    # Find first incomplete step
    incomplete_step = None
    for step in current_plan.steps:
        if not step.execution_res:
            incomplete_step = step
            break

    if not incomplete_step:
        return "planner"

    # 执行下一个step的逻辑
    if incomplete_step.step_type == StepType.RESEARCH:
        return "researcher"
    if incomplete_step.step_type == StepType.PROCESSING:
        return "coder"
    return "planner"

def planner_node(
    state: State, config: RunnableConfig
) -> Command[Literal["human_feedback", "reporter"]]:
    """Planner node that generate the full plan."""
    logger.info("Planner generating full plan")
    configurable = Configuration.from_runnable_config(config)
    plan_iterations = state["plan_iterations"] if state.get("plan_iterations", 0) else 0
    messages = apply_prompt_template("planner", state, configurable)
    logger.info(f"planner_node:{state}")

    if state.get("enable_background_investigation") and state.get(
        "background_investigation_results"
    ): 
        messages += [
            {
                "role": "user",
                "content": (
                    "background investigation results of user query:\n"
                    + state["background_investigation_results"]
                    + "\n"
                ),
            }
        ]

    if configurable.enable_deep_thinking:
        llm = get_llm_by_type("reasoning")
    elif AGENT_LLM_MAP["planner"] == "basic":
        llm = get_llm_by_type("basic").with_structured_output(
            Plan,
            # method="json_mode",
        )
    else:
        llm = get_llm_by_type(AGENT_LLM_MAP["planner"])

    # if the plan iterations is greater than the max plan iterations, return the reporter node
    # max_plan_iterations 默认是1，所以直接到reporter
    if plan_iterations >= configurable.max_plan_iterations:
        return Command(goto="reporter")
    ...

def reporter_node(state: State, config: RunnableConfig):
    """Reporter node that write a final report."""
    logger.info("Reporter write final report")
    configurable = Configuration.from_runnable_config(config)
    current_plan = state.get("current_plan")
    input_ = {
        "messages": [
            HumanMessage(
                f"# Research Requirements\n\n## Task\n\n{current_plan.title}\n\n## Description\n\n{current_plan.thought}"
            )
        ],
        "locale": state.get("locale", "en-US"),
    }
    invoke_messages = apply_prompt_template("reporter", input_, configurable)
    observations = state.get("observations", [])

    # Add a reminder about the new report format, citation style, and table usage
    invoke_messages.append(
        HumanMessage(
            content="IMPORTANT: Structure your report according to the format in the prompt. Remember to include:\n\n1. Key Points - A bulleted list of the most important findings\n2. Overview - A brief introduction to the topic\n3. Detailed Analysis - Organized into logical sections\n4. Survey Note (optional) - For more comprehensive reports\n5. Key Citations - List all references at the end\n\nFor citations, DO NOT include inline citations in the text. Instead, place all citations in the 'Key Citations' section at the end using the format: `- [Source Title](URL)`. Include an empty line between each citation for better readability.\n\nPRIORITIZE USING MARKDOWN TABLES for data presentation and comparison. Use tables whenever presenting comparative data, statistics, features, or options. Structure tables with clear headers and aligned columns. Example table format:\n\n| Feature | Description | Pros | Cons |\n|---------|-------------|------|------|\n| Feature 1 | Description 1 | Pros 1 | Cons 1 |\n| Feature 2 | Description 2 | Pros 2 | Cons 2 |",
            name="system",
        )
    )

    # 拼接消息，发给llm
    for observation in observations:
        invoke_messages.append(
            HumanMessage(
                content=f"Below are some observations for the research task:\n\n{observation}",
                name="observation",
            )
        )
    logger.debug(f"Current invoke messages: {invoke_messages}")
    response = get_llm_by_type(AGENT_LLM_MAP["reporter"]).invoke(invoke_messages)
    response_content = response.content
    logger.info(f"reporter response: {response_content}")

    return {"final_report": response_content}