cmdc

defmodule CMDC.Tool.CompactConversation do
  @moduledoc """
  手动触发上下文压缩，对标 DeepAgents `compact_conversation` 工具。

  在消息历史过长但尚未达到自动压缩阈值时，Agent 可主动调用此工具
  立即执行压缩，释放上下文窗口空间。

  ## 执行流程

  1. 读取当前 `Agent.State`（通过 `agent_pid` 上下文字段）
  2. 调用 `CMDC.Agent.Compactor.force_compact/1`
  3. 更新 Agent 状态
  4. 返回压缩统计信息

  ## 与 Agent 的交互

  此工具需要在 context 中包含 `agent_pid`，由 Agent 在构建工具上下文时注入。
  若无 `agent_pid`，工具仍可运行但不会实际修改 Agent 状态。

  ## 返回格式

      Conversation compacted successfully.
      - Messages before: 42
      - Messages after: 8
      - Messages removed: 34
      - History saved to: /conversation_history/session-abc.md
  """

  @behaviour CMDC.Tool

  alias CMDC.Agent.Compactor

  @impl true
  def name, do: "compact_conversation"

  @impl true
  def description do
    "Manually compact the conversation history to free up context window space. " <>
      "Use this when the conversation is getting long and you need more room " <>
      "for complex tasks. The full history is saved to a file for reference."
  end

  @impl true
  def meta(_), do: "CompactConversation"

  @impl true
  def parameters do
    %{
      "type" => "object",
      "properties" => %{
        "reason" => %{
          "type" => "string",
          "description" =>
            "Optional reason for compacting (e.g. \"context getting long before complex task\")."
        }
      },
      "required" => []
    }
  end

  @impl true
  def execute(args, context) do
    reason = Map.get(args, "reason", "manual compact")
    agent_pid = Map.get(context, :agent_pid)

    if is_pid(agent_pid) and Process.alive?(agent_pid) do
      compact_via_agent(agent_pid, reason)
    else
      {:error,
       "compact_conversation requires a running Agent process. " <>
         "This tool must be called within an active Agent session."}
    end
  end

  # ==========================================================================
  # 私有辅助
  # ==========================================================================

  defp compact_via_agent(agent_pid, reason) do
    state = CMDC.Agent.get_state(agent_pid)
    before_count = length(state.messages)

    case Compactor.force_compact(state) do
      {:compacted, new_state} ->
        after_count = length(new_state.messages)
        removed = before_count - after_count

        apply_state_update(agent_pid, new_state)

        offload_path = extract_offload_path(new_state, state)
        {:ok, build_result(before_count, after_count, removed, offload_path, reason)}

      {:skip, _state} ->
        {:ok,
         "No compaction needed — conversation is too short to compact " <>
           "(#{before_count} messages)."}
    end
  end

  defp apply_state_update(agent_pid, new_state) do
    :sys.replace_state(agent_pid, fn {state_name, _old_state} ->
      {state_name, new_state}
    end)
  rescue
    _ -> :ok
  end

  defp extract_offload_path(new_state, old_state) do
    opts = Compactor.compact_config(old_state)
    path = Path.join(opts.offload_dir, "#{new_state.session_id}.md")

    full = Path.join(new_state.working_dir, path)

    if File.exists?(full), do: path, else: nil
  end

  defp build_result(before, after_count, removed, offload_path, reason) do
    lines = [
      "Conversation compacted successfully. (reason: #{reason})",
      "- Messages before: #{before}",
      "- Messages after: #{after_count}",
      "- Messages removed: #{removed}"
    ]

    lines =
      if offload_path do
        lines ++ ["- History saved to: #{offload_path}"]
      else
        lines
      end

    Enum.join(lines, "\n")
  end
end