defmodule Jido.Tools.LuaEval do
  @moduledoc """
  Execute a Lua code string in a sandboxed VM and return the values.

  ## Features

  - **Safe by default:** Uses Lua.ex sandbox defaults to disable unsafe functions
  - **Timeout protection:** Configurable timeout with task isolation
  - **Call-depth protection:** Optional recursion guard for nested Lua calls
  - **Global injection:** Pass Elixir values into the Lua environment
  - **Flexible returns:** Return all values or just the first one

  ## Security

  By default, the following unsafe Lua libraries are disabled:
  - `os` (getenv, execute, exit, etc.)
  - `io` and `file`
  - `package`, `require`, `dofile`
  - `load`, `loadfile`, `loadstring`

  Safe libraries remain enabled:
  - `string`, `math`, `table`
  - Basic Lua operations

  Set `enable_unsafe_libs: true` to disable Lua.ex capability sandboxing (use with
  caution). Lua.ex 1.0 still has no host shell or host filesystem access.
  Set `max_call_depth` to a positive integer to cap nested Lua function calls.

  ## Examples

      # Simple arithmetic
      iex> Jido.Tools.LuaEval.run(%{code: "return 2 + 2"}, %{})
      {:ok, %{results: [4]}}

      # With globals
      iex> Jido.Tools.LuaEval.run(%{
        code: "return x + 5",
        globals: %{"x" => 10}
      }, %{})
      {:ok, %{results: [15]}}

      # Return first value only
      iex> Jido.Tools.LuaEval.run(%{
        code: "return 1, 2, 3",
        return_mode: :first
      }, %{})
      {:ok, %{result: 1}}

      # Timeout protection
      iex> Jido.Tools.LuaEval.run(%{
        code: "while true do end",
        timeout_ms: 50
      }, %{})
      {:error, %Jido.Action.Error.TimeoutError{timeout: 50}}
  """

  alias Jido.Action.Error

  @deadline_key :__jido_deadline_ms__
  @default_max_heap_bytes 64 * 1024 * 1024

  use Jido.Action,
    name: "lua_eval",
    description: "Execute a Lua code string in a sandboxed VM and return the values.",
    category: "scripting",
    vsn: "0.1.0",
    schema: [
      code: [
        type: :string,
        required: true,
        doc: "Lua code to execute (typically ends with `return ...` to produce values)."
      ],
      globals: [
        type: :map,
        default: %{},
        doc: "Map of global variables to inject into Lua state. Keys can be atoms or strings."
      ],
      return_mode: [
        type: {:in, [:list, :first]},
        default: :list,
        doc:
          "Shape of output: :list returns all values under `results`, :first returns only the first under `result`."
      ],
      enable_unsafe_libs: [
        type: :boolean,
        default: false,
        doc: "Enable unsafe libs (os/package/require/etc.) by disabling sandboxing."
      ],
      timeout_ms: [
        type: :non_neg_integer,
        default: 1000,
        doc: "Execution timeout in milliseconds."
      ],
      max_call_depth: [
        type: :non_neg_integer,
        default: 0,
        doc: "Maximum nested Lua call depth (0 = disabled / infinity)."
      ],
      max_heap_bytes: [
        type: :non_neg_integer,
        default: @default_max_heap_bytes,
        doc: "Per-process heap limit in bytes (0 = disabled)."
      ]
    ],
    output_schema: []

  @impl true
  def run(params, context) do
    if Code.ensure_loaded?(Lua) do
      requested_timeout_ms = Map.get(params, :timeout_ms, 1000)

      case effective_timeout_ms(requested_timeout_ms, context) do
        {:ok, timeout_ms} ->
          parent = self()
          ref = make_ref()

          {:ok, pid} =
            Task.Supervisor.start_child(Jido.Action.TaskSupervisor, fn ->
              send(parent, {:lua_eval_result, ref, do_run(params)})
            end)

          watchdog_pid = start_lua_watchdog(parent, pid)
          monitor_ref = Process.monitor(pid)

          case await_lua_result(ref, pid, monitor_ref, timeout_ms) do
            {:ok, result} ->
              cleanup_lua_task(ref, monitor_ref, watchdog_pid)
              result

            {:exit, reason} ->
              cleanup_lua_task(ref, monitor_ref, watchdog_pid)
              return_error(:lua_error, "Lua task exited: #{inspect(reason)}")

            :timeout ->
              _ = Process.exit(pid, :kill)
              wait_for_lua_down(monitor_ref, pid, 100)
              cleanup_lua_task(ref, monitor_ref, watchdog_pid)
              timeout_error(timeout_ms)
          end

        {:error, error} ->
          {:error, error}
      end
    else
      msg =
        "Lua library (:lua) is not available. Add {:lua, \"~> 1.0.0-rc\"} to your deps and run mix deps.get"

      return_error(:dependency_error, msg)
    end
  end

  @doc false
  def await_lua_result(ref, pid, monitor_ref, timeout_ms) do
    receive do
      {:lua_eval_result, ^ref, result} ->
        {:ok, result}

      {:DOWN, ^monitor_ref, :process, ^pid, :normal} ->
        wait_for_lua_result(ref, 100)

      {:DOWN, ^monitor_ref, :process, ^pid, reason} ->
        {:exit, reason}
    after
      timeout_ms ->
        :timeout
    end
  end

  defp wait_for_lua_result(ref, wait_ms) do
    receive do
      {:lua_eval_result, ^ref, result} -> {:ok, result}
    after
      wait_ms -> {:exit, :normal}
    end
  end

  defp wait_for_lua_down(monitor_ref, pid, wait_ms) do
    receive do
      {:DOWN, ^monitor_ref, :process, ^pid, _reason} -> :ok
    after
      wait_ms -> :ok
    end
  end

  defp cleanup_lua_task(ref, monitor_ref, watchdog_pid) do
    send(watchdog_pid, :stop)
    Process.demonitor(monitor_ref, [:flush])
    flush_lua_results(ref)
  end

  defp flush_lua_results(ref) do
    receive do
      {:lua_eval_result, ^ref, _result} ->
        flush_lua_results(ref)
    after
      0 -> :ok
    end
  end

  defp start_lua_watchdog(parent, lua_pid) do
    spawn(fn ->
      parent_ref = Process.monitor(parent)
      lua_ref = Process.monitor(lua_pid)

      receive do
        {:DOWN, ^parent_ref, :process, ^parent, _reason} ->
          if Process.alive?(lua_pid), do: Process.exit(lua_pid, :kill)
          Process.demonitor(lua_ref, [:flush])

        {:DOWN, ^lua_ref, :process, ^lua_pid, _reason} ->
          Process.demonitor(parent_ref, [:flush])

        :stop ->
          Process.demonitor(parent_ref, [:flush])
          Process.demonitor(lua_ref, [:flush])
      end
    end)
  end

  defp effective_timeout_ms(timeout_ms, context) when is_map(context) do
    case context[@deadline_key] do
      deadline_ms when is_integer(deadline_ms) ->
        now = System.monotonic_time(:millisecond)
        remaining = deadline_ms - now

        if remaining <= 0 do
          {:error,
           Error.timeout_error("Execution deadline exceeded before Lua dispatch", %{
             deadline_ms: deadline_ms,
             now_ms: now
           })}
        else
          {:ok, min(timeout_ms, remaining)}
        end

      _ ->
        {:ok, timeout_ms}
    end
  end

  defp effective_timeout_ms(timeout_ms, _context), do: {:ok, timeout_ms}

  defp do_run(params) do
    code = Map.fetch!(params, :code)
    globals = Map.get(params, :globals, %{})
    return_mode = Map.get(params, :return_mode, :list)
    enable_unsafe_libs = Map.get(params, :enable_unsafe_libs, false)
    max_call_depth = Map.get(params, :max_call_depth, 0)
    max_heap_bytes = Map.get(params, :max_heap_bytes, @default_max_heap_bytes)

    if is_integer(max_heap_bytes) and max_heap_bytes > 0 do
      :erlang.process_flag(:max_heap_size, %{
        size: bytes_to_heap_words(max_heap_bytes),
        kill: true,
        error_logger: false
      })
    end

    try do
      lua =
        enable_unsafe_libs
        |> lua_options(max_call_depth)
        |> Lua.new()
        |> inject_globals(globals)

      {values, _state} = Lua.eval!(lua, code)

      result =
        case return_mode do
          :first -> %{result: List.first(values)}
          _ -> %{results: values}
        end

      {:ok, result}
    rescue
      e in Lua.CompilerException ->
        return_error(:compile_error, Exception.message(e))

      e in Lua.RuntimeException ->
        return_error(:lua_error, Exception.message(e))

      e ->
        return_error(:lua_error, Exception.message(e))
    end
  end

  defp lua_options(enable_unsafe_libs, max_call_depth) do
    []
    |> maybe_disable_sandbox(enable_unsafe_libs)
    |> maybe_put_max_call_depth(max_call_depth)
  end

  defp maybe_disable_sandbox(opts, true), do: Keyword.put(opts, :sandboxed, [])
  defp maybe_disable_sandbox(opts, _), do: opts

  defp maybe_put_max_call_depth(opts, max_call_depth)
       when is_integer(max_call_depth) and max_call_depth > 0 do
    Keyword.put(opts, :max_call_depth, max_call_depth)
  end

  defp maybe_put_max_call_depth(opts, _), do: opts

  defp bytes_to_heap_words(bytes) do
    bytes
    |> div(:erlang.system_info(:wordsize))
    |> max(1)
  end

  defp inject_globals(lua, globals) do
    Enum.reduce(globals || %{}, lua, fn {key, value}, acc ->
      {encoded, acc2} = Lua.encode!(acc, value)
      path = if is_list(key), do: key, else: [key]
      Lua.set!(acc2, path, encoded)
    end)
  end

  defp return_error(type, message) do
    {:error,
     Error.execution_error(message, %{
       type: type,
       reason: %{type: type, message: message}
     })}
  end

  defp timeout_error(timeout_ms) do
    {:error,
     Error.timeout_error("Lua execution timed out after #{timeout_ms}ms", %{
       timeout: timeout_ms,
       reason: %{type: :timeout, timeout_ms: timeout_ms}
     })}
  end
end