# Covers ADR-006, ADR-007 (MCP hosted tool + session resume)
Mix.Task.run("app.start")

alias Codex.{AgentRunner, RunConfig, Tools}
alias Codex.Agent, as: CodexAgent
alias Codex.Items.AgentMessage

defmodule CodexExamples.StubMcpTransport do
  @moduledoc false

  def start_link do
    Agent.start_link(fn -> %{last: nil, call_attempts: 0} end)
  end

  def send(pid, payload) do
    Agent.update(pid, &Map.put(&1, :last, payload))
    :ok
  end

  def recv(pid) do
    Agent.get_and_update(pid, fn %{last: request} = state ->
      case request["type"] do
        "handshake" ->
          {{:ok, %{"type" => "handshake.ack", "capabilities" => %{"tools" => true}}}, state}

        "list_tools" ->
          tools = [%{"name" => "stub.echo", "description" => "echoes arguments"}]
          {{:ok, %{"tools" => tools}}, state}

        "call_tool" ->
          attempt = state.call_attempts + 1
          updated = %{state | call_attempts: attempt}

          if attempt == 1 do
            {{:ok, %{"error" => "transient"}}, updated}
          else
            args = Map.get(request, "arguments") || %{}
            {{:ok, %{"result" => %{"echo" => args}}}, updated}
          end

        _ ->
          {{:error, :unknown_request}, state}
      end
    end)
  end
end

defmodule CodexExamples.MemorySession do
  @moduledoc false
  @behaviour Codex.Session

  def start_link, do: Agent.start_link(fn -> [] end)

  @impl true
  def load(pid), do: {:ok, Agent.get(pid, & &1)}

  @impl true
  def save(pid, entry) do
    Agent.update(pid, &[entry | &1])
    :ok
  end

  @impl true
  def clear(pid) do
    Agent.update(pid, fn _ -> [] end)
    :ok
  end
end

defmodule CodexExamples.LiveMcpAndSessions do
  @moduledoc false

  def main(argv) do
    {prompt1, prompt2} = parse_prompts(argv)

    Tools.reset!()

    {:ok, transport} = CodexExamples.StubMcpTransport.start_link()

    {:ok, client} =
      Codex.MCP.Client.handshake({CodexExamples.StubMcpTransport, transport},
        client: "codex-elixir-demo",
        version: "0.1.0"
      )

    {:ok, tools, client} = Codex.MCP.Client.list_tools(client, allow: ["stub.echo"])
    IO.puts("MCP tools (filtered): #{inspect(Enum.map(tools, & &1["name"]))}")

    {:ok, _} =
      Tools.register(Codex.Tools.HostedMcpTool,
        name: "hosted_mcp",
        metadata: %{
          client: client,
          tool: "stub.echo",
          retries: 1,
          backoff: &mcp_backoff/1
        }
      )

    {:ok, agent} =
      CodexAgent.new(%{
        name: "McpSessionAgent",
        instructions:
          "Use hosted_mcp (stub.echo) once to mirror the request, then answer concisely. Keep the session id in mind.",
        tools: ["hosted_mcp"],
        reset_tool_choice: true
      })

    {:ok, session_pid} = CodexExamples.MemorySession.start_link()

    {:ok, codex_opts} =
      Codex.Options.new(%{
        codex_path_override: fetch_codex_path!()
      })

    {:ok, thread} = Codex.start_thread(codex_opts)

    run_config =
      RunConfig.new(%{
        session: {CodexExamples.MemorySession, session_pid},
        conversation_id: "demo-conversation"
      })
      |> unwrap!("run config")

    {:ok, first} = AgentRunner.run(thread, prompt1, %{agent: agent, run_config: run_config})
    IO.puts("First response: #{render_response(first.final_response)}")

    resume_config =
      RunConfig.new(%{
        session: {CodexExamples.MemorySession, session_pid},
        conversation_id: "demo-conversation",
        previous_response_id: "demo-prev-response"
      })
      |> unwrap!("resume config")

    {:ok, second} =
      AgentRunner.run(first.thread, prompt2, %{agent: agent, run_config: resume_config})

    IO.puts("Resumed response: #{render_response(second.final_response)}")
    IO.puts("Session stored entries: #{inspect(Agent.get(session_pid, &Enum.reverse/1))}")
  end

  defp mcp_backoff(attempt) do
    delay = attempt * 100
    Process.sleep(delay)
    IO.puts("Retrying MCP call (attempt #{attempt}) after #{delay}ms")
  end

  defp parse_prompts([]) do
    {
      "Ask hosted_mcp to echo a short note about sessions.",
      "Resume the same session and ask for a one-line reminder."
    }
  end

  defp parse_prompts([first | rest]) do
    {first, Enum.join(rest, " ")}
  end

  defp render_response(%AgentMessage{text: text}), do: text
  defp render_response(%{"text" => text}), do: text
  defp render_response(nil), do: "<no response>"
  defp render_response(other), do: inspect(other)

  defp unwrap!({:ok, value}, _label), do: value

  defp unwrap!({:error, reason}, label),
    do: Mix.raise("Failed to build #{label}: #{inspect(reason)}")

  defp fetch_codex_path! do
    System.get_env("CODEX_PATH") ||
      System.find_executable("codex") ||
      Mix.raise("""
      Unable to locate the `codex` CLI.
      Install the Codex CLI and ensure it is on your PATH or set CODEX_PATH.
      """)
  end
end

CodexExamples.LiveMcpAndSessions.main(System.argv())