defmodule Boam do
  @moduledoc """
  High-level entrypoint for running JavaScript through Boa from Elixir.

  `Boam` wraps a dedicated Boa runtime behind a `GenServer`. Each runtime owns a
  single Rust worker thread because Boa `Context` values are not thread-safe.

  JavaScript code can call back into Elixir with `beam.call(name, ...args)`. The
  dispatch itself happens through a separate BEAM process, which keeps the
  runtime process focused on driving the JavaScript engine.

  You can either:

    * expose Elixir handlers directly as JavaScript functions with `:expose`
    * run startup JavaScript with `:prelude`
    * generate shim code manually with `Boam.JS.export_prelude/1`

  ## Quick Start

  ```elixir
  {:ok, runtime} =
    Boam.start_link(
      exports: %{
        sum: fn [left, right] -> left + right end
      }
    )

  Boam.eval(runtime, "1 + 2")
  #=> {:ok, 3}

  Boam.eval(runtime, "beam.call('sum', 2, 3)")
  #=> {:ok, 5}
  ```

  Or expose a nested JavaScript API directly:

  ```elixir
  {:ok, runtime} =
    Boam.start_link(
      expose: %{
        console: %{
          log: fn [message] -> "logged: \#{message}" end
        }
      }
    )

  Boam.eval(runtime, "console.log('hello')")
  #=> {:ok, "logged: hello"}
  ```

  ## Value Bridge

  Values crossing between JavaScript and Elixir are intentionally restricted to
  JSON-compatible data:

    * `null` maps to `nil`
    * booleans, numbers, strings, arrays, and objects round-trip normally
    * top-level JavaScript `undefined` is returned as `:undefined`
    * `undefined` cannot be passed through `beam.call/1`

  Returned JavaScript objects are serialized through Boa's JSON conversion, so
  object keys come back to Elixir as strings.

  ## Architecture

    * [`Boam.Runtime`](`Boam.Runtime`) owns the Rust runtime resource
    * [`Boam.Dispatcher`](`Boam.Dispatcher`) receives `beam.call(...)` requests
    * [`Boam.JS`](`Boam.JS`) generates JavaScript shim preludes
    * `Boam` provides the small public entrypoint for the common case
  """

  alias Boam.Runtime

  @type start_option ::
          {:name, GenServer.name()}
          | {:dispatcher, pid()}
          | {:exports, map() | keyword()}
          | {:expose, Boam.JS.export_tree()}
          | {:prelude, String.t() | [String.t()]}
          | {:fallback, (String.t(), list() -> term())}
          | {:dispatch_timeout, timeout()}

  @doc """
  Starts a Boa runtime process.

  This is a convenience wrapper around `#{inspect(Runtime)}.start_link/1`.

  See `#{inspect(Runtime)}` for the full option contract.
  """
  @spec start_link([start_option()]) :: GenServer.on_start()
  def start_link(opts \\ []) do
    Runtime.start_link(opts)
  end

  @doc """
  Evaluates JavaScript source code inside a running runtime.

  This is a convenience wrapper around `#{inspect(Runtime)}.eval/2`.
  """
  @spec eval(GenServer.server(), String.t()) :: {:ok, term()} | {:error, String.t()}
  def eval(runtime, source) do
    Runtime.eval(runtime, source)
  end
end