defmodule PtcRunner do
  @moduledoc """
  A BEAM-native Programmatic Tool Calling (PTC) runner.

  PtcRunner enables LLMs to write safe programs that orchestrate tools
  and transform data inside a sandboxed environment.

  ## Examples

      iex> program = ~s({"program": {"op": "literal", "value": 42}})
      iex> {:ok, result, _metrics} = PtcRunner.run(program)
      iex> result
      42
  """

  alias PtcRunner.Context
  alias PtcRunner.Parser
  alias PtcRunner.Sandbox
  alias PtcRunner.Validator

  @typedoc """
  Execution metrics for a program run.
  """
  @type metrics :: %{
          duration_ms: integer(),
          memory_bytes: integer()
        }

  @typedoc """
  Error types returned by PtcRunner operations.
  """
  @type error ::
          {:parse_error, String.t()}
          | {:validation_error, String.t()}
          | {:execution_error, String.t()}
          | {:timeout, non_neg_integer()}
          | {:memory_exceeded, non_neg_integer()}

  @doc """
  Runs a PTC program and returns the result with metrics.

  ## Arguments
    - program: JSON string or parsed map representing the program
    - opts: Execution options

  ## Options
    - `:context` - Map of pre-bound variables (default: `%{}`)
    - `:tools` - Tool registry (default: `%{}`)
    - `:timeout` - Timeout in milliseconds (default: 1000)
    - `:max_heap` - Max heap size in words (default: 1_250_000)

  ## Returns
    - `{:ok, result, metrics}` on success
    - `{:error, reason}` on failure

  ## Examples

      iex> {:ok, result, _metrics} = PtcRunner.run(~s({"program": {"op": "literal", "value": 42}}))
      iex> result
      42
  """
  @spec run(String.t() | map(), keyword()) ::
          {:ok, any(), metrics()} | {:error, error()}

  def run(program, opts \\ []) do
    with {:ok, ast} <- Parser.parse(program),
         :ok <- Validator.validate(ast) do
      context_map = Keyword.get(opts, :context, %{})
      tools = Keyword.get(opts, :tools, %{})

      with :ok <- validate_tools(tools) do
        context = Context.new(context_map, tools)

        sandbox_opts = [
          timeout: Keyword.get(opts, :timeout, 1000),
          max_heap: Keyword.get(opts, :max_heap, 1_250_000)
        ]

        Sandbox.execute(ast, context, sandbox_opts)
      end
    else
      {:error, reason} -> {:error, reason}
    end
  end

  @doc """
  Runs a PTC program, raising on error.

  ## Arguments
    - program: JSON string or parsed map representing the program
    - opts: Execution options (same as `run/2`)

  ## Returns
    - The result value (metrics are discarded)

  ## Raises
    - Raises an error if parsing, validation, or execution fails

  ## Examples

      iex> result = PtcRunner.run!(~s({"program": {"op": "literal", "value": 42}}))
      iex> result
      42
  """
  @spec run!(String.t() | map(), keyword()) :: any()

  def run!(program, opts \\ []) do
    case run(program, opts) do
      {:ok, result, _metrics} -> result
      {:error, reason} -> raise "PtcRunner error: #{inspect(reason)}"
    end
  end

  defp validate_tools(tools) do
    invalid_tools =
      tools
      |> Enum.reject(fn {_name, fun} -> is_function(fun, 1) end)
      |> Enum.map(fn {name, _fun} -> name end)

    case invalid_tools do
      [] ->
        :ok

      names ->
        {:error,
         {:validation_error,
          "Tools must be functions with arity 1. Invalid: #{Enum.join(names, ", ")}"}}
    end
  end
end