defmodule Snakepit do
  @moduledoc """
  Snakepit - A generalized high-performance pooler and session manager.

  Extracted from DSPex V3 pool implementation, Snakepit provides:
  - Concurrent worker initialization and management
  - Stateless pool system with session affinity
  - Generalized adapter pattern for any external process
  - High-performance OTP-based process management

  ## Basic Usage

      # Configure in config/config.exs
      config :snakepit,
        pooling_enabled: true,
        adapter_module: YourAdapter

      # Execute commands on any available worker
      {:ok, result} = Snakepit.execute("ping", %{test: true})

      # Session-based execution with worker affinity
      {:ok, result} = Snakepit.execute_in_session("my_session", "command", %{})

  ## Domain-Specific Helpers

  For ML/DSP workflows with program management, see `Snakepit.SessionHelpers`:

      # ML program creation and execution
      {:ok, result} = Snakepit.SessionHelpers.execute_program_command(
        "session_id", "create_program", %{signature: "input -> output"}
      )
  """

  # Type definitions
  @type command :: String.t()
  @type args :: map()
  @type result :: term()
  @type session_id :: String.t()
  @type callback_fn :: (term() -> any())
  @type pool_name :: atom() | pid()

  @doc """
  Convenience function to execute commands on the pool.

  ## Examples

      {:ok, result} = Snakepit.execute("ping", %{test: true})

  ## Options

    * `:pool` - The pool to use (default: `Snakepit.Pool`)
    * `:timeout` - Request timeout in ms (default: 60000)
    * `:session_id` - Execute with session affinity
  """
  @spec execute(command(), args(), keyword()) :: {:ok, result()} | {:error, Snakepit.Error.t()}
  def execute(command, args, opts \\ []) do
    Snakepit.Pool.execute(command, args, opts)
  end

  @doc """
  Executes a command in session context with worker affinity.

  This function executes commands with session-based worker affinity,
  ensuring that subsequent calls with the same session_id prefer
  the same worker when possible for state continuity.

  Args are passed through unchanged - no domain-specific enhancement.
  For ML/DSP program workflows, use `Snakepit.SessionHelpers.execute_program_command/4`.
  """
  @spec execute_in_session(session_id(), command(), args(), keyword()) ::
          {:ok, result()} | {:error, Snakepit.Error.t()}
  def execute_in_session(session_id, command, args, opts \\ []) do
    # Add session_id to opts for session affinity
    opts_with_session = Keyword.put(opts, :session_id, session_id)

    # Execute command with session affinity (no args enhancement)
    execute(command, args, opts_with_session)
  end

  @doc """
  Get pool statistics.

  Returns aggregate stats across all pools or stats for a specific pool.
  """
  @spec get_stats(pool_name()) :: map()
  def get_stats(pool \\ Snakepit.Pool) do
    Snakepit.Pool.get_stats(pool)
  end

  @doc """
  List workers from the pool.

  Returns a list of worker IDs.
  """
  @spec list_workers(pool_name()) :: [String.t()]
  def list_workers(pool \\ Snakepit.Pool) do
    Snakepit.Pool.list_workers(pool)
  end

  @doc """
  Executes a streaming command with a callback function.

  ## Examples

      Snakepit.execute_stream("batch_inference", %{items: [...]}, fn chunk ->
        IO.puts("Received: \#{inspect(chunk)}")
      end)

  ## Options

    * `:pool` - The pool to use (default: `Snakepit.Pool`)
    * `:timeout` - Request timeout in ms (default: 300000)
    * `:session_id` - Run in a specific session

  ## Returns

  Returns `:ok` on success or `{:error, %Snakepit.Error{}}` on failure.

  Note: Streaming is only supported with gRPC adapters.
  """
  @spec execute_stream(command(), args(), callback_fn(), keyword()) ::
          :ok | {:error, Snakepit.Error.t()}
  def execute_stream(command, args \\ %{}, callback_fn, opts \\ []) do
    ensure_started!()

    adapter = Application.get_env(:snakepit, :adapter_module)

    unless function_exported?(adapter, :uses_grpc?, 0) and adapter.uses_grpc?() do
      {:error,
       Snakepit.Error.validation_error("Streaming not supported by adapter", %{
         adapter: adapter
       })}
    else
      Snakepit.Pool.execute_stream(command, args, callback_fn, opts)
    end
  end

  @doc """
  Executes a command in a session with a callback function.
  """
  @spec execute_in_session_stream(session_id(), command(), args(), callback_fn(), keyword()) ::
          :ok | {:error, Snakepit.Error.t()}
  def execute_in_session_stream(session_id, command, args \\ %{}, callback_fn, opts \\ []) do
    ensure_started!()

    adapter = Application.get_env(:snakepit, :adapter_module)

    unless function_exported?(adapter, :uses_grpc?, 0) and adapter.uses_grpc?() do
      {:error,
       Snakepit.Error.validation_error("Streaming not supported by adapter", %{
         adapter: adapter
       })}
    else
      opts_with_session = Keyword.put(opts, :session_id, session_id)
      Snakepit.Pool.execute_stream(command, args, callback_fn, opts_with_session)
    end
  end

  defp ensure_started! do
    case Application.ensure_all_started(:snakepit) do
      {:ok, _} -> :ok
      {:error, _} -> raise "Snakepit application not started"
    end
  end

  @doc """
  Starts the Snakepit application, executes a given function,
  and ensures graceful shutdown.

  This is the recommended way to use Snakepit for short-lived scripts or
  Mix tasks to prevent orphaned processes.

  It handles the full OTP application lifecycle (start, run, stop)
  automatically.

  ## Examples

      # In a Mix task
      Snakepit.run_as_script(fn ->
        {:ok, result} = Snakepit.execute("my_command", %{data: "value"})
        IO.inspect(result)
      end)

      # For demos or scripts
      Snakepit.run_as_script(fn ->
        MyApp.run_load_test()
      end)

  ## Options

    * `:timeout` - Maximum time to wait for pool initialization (default: 15000ms)

  ## Returns

  Returns the result of the provided function, or `{:error, reason}` if
  the pool fails to initialize.
  """
  @spec run_as_script((-> any()), keyword()) :: any() | {:error, term()}
  def run_as_script(fun, opts \\ []) when is_function(fun, 0) do
    timeout = Keyword.get(opts, :timeout, 15_000)

    # Ensure all dependencies are started, including Snakepit itself
    {:ok, _apps} = Application.ensure_all_started(:snakepit)

    # Deterministically wait for the pool to be fully initialized
    case Snakepit.Pool.await_ready(Snakepit.Pool, timeout) do
      :ok ->
        try do
          fun.()
        after
          IO.puts("\n[Snakepit] Script execution finished. Shutting down gracefully...")

          # Monitor the supervisor to wait for actual shutdown signal
          case Process.whereis(Snakepit.Supervisor) do
            nil ->
              # Already shut down
              IO.puts("[Snakepit] Shutdown complete (supervisor already terminated).")

            supervisor_pid ->
              ref = Process.monitor(supervisor_pid)
              Application.stop(:snakepit)

              # Wait for :DOWN signal from BEAM - no guessing with sleep
              receive do
                {:DOWN, ^ref, :process, ^supervisor_pid, _reason} ->
                  IO.puts("[Snakepit] Shutdown complete (confirmed via :DOWN signal).")
              after
                5_000 ->
                  IO.puts(
                    "[Snakepit] Warning: Shutdown confirmation timeout after 5s. " <>
                      "Proceeding anyway."
                  )
              end
          end
        end

      {:error, %Snakepit.Error{category: :timeout}} ->
        IO.puts("[Snakepit] Error: Pool failed to initialize within #{timeout}ms")
        Application.stop(:snakepit)
        {:error, :pool_initialization_timeout}
    end
  end

  # Note: For ML/DSP program management functionality, see Snakepit.SessionHelpers
end