defmodule Dds do
  @moduledoc """
  The dds toolchain, bundled. This module is a LOCATOR AND RUNNER,
  nothing more — the instruments are the bundled Python (the same
  bytes as the tagged toolchain repo), and all semantics live there.

  Runtime resolution, best first:

  1. **Pythonx** (embedded CPython, hermetic) — when the optional
     `:pythonx` dep is present, `mix deps.get` is the ONLY
     prerequisite: pythonx provisions a standalone interpreter and the
     tree-sitter wheels itself (pinned below), in-process, no system
     Python, no PATH. The mechanical witness and evidence replay work
     out of the box.
  2. `uv` on PATH — same hermetic properties via subprocess.
  3. `python3` (>= 3.9) — stdlib legs directly; tree-sitter legs
     degrade with the toolchain's own honest hints.
  4. None — a clear error naming the options.
  """

  @pythonx_project """
  [project]
  name = "dds-runner"
  version = "0.0.0"
  requires-python = ">=3.10"
  dependencies = ["tree-sitter", "tree-sitter-elixir"]
  """

  @tree_deps ["tree-sitter", "tree-sitter-elixir"]

  @doc "Run the bundled CLI with `args`; exits the VM with its exit code on failure."
  def run(args) when is_list(args) do
    cli = Path.join(:code.priv_dir(:dds), "toolchain/cli.py")

    status =
      cond do
        Code.ensure_loaded?(Pythonx) -> run_pythonx(cli, args)
        uv = System.find_executable("uv") -> run_cmd(uv, uv_args(cli, args))
        py = System.find_executable("python3") -> run_cmd(py, [cli | args])
        true -> raise_no_runtime()
      end

    if status != 0, do: exit({:shutdown, status})
    :ok
  end

  defp run_pythonx(cli, args) do
    # embedded CPython: pythonx downloads/caches a standalone build and
    # the pinned deps; the toolchain runs in-process. SystemExit is the
    # CLI's normal exit path — catch it and surface the code.
    {:ok, _} = Application.ensure_all_started(:pythonx)
    Pythonx.uv_init(@pythonx_project)

    {result, _globals} =
      Pythonx.eval(
        """
        import runpy, sys
        sys.argv = ["dds", *[a.decode() for a in args]]
        _code = 0
        try:
            runpy.run_path(cli.decode(), run_name="__main__")
        except SystemExit as e:
            _code = int(e.code or 0)
        _code
        """,
        %{"args" => args, "cli" => cli}
      )

    result |> Pythonx.decode() |> trunc()
  end

  defp uv_args(cli, args) do
    ["run", "--quiet"] ++ Enum.flat_map(@tree_deps, &["--with", &1]) ++ ["--", cli | args]
  end

  defp run_cmd(cmd, argv) do
    {_, status} =
      System.cmd(cmd, argv, into: IO.stream(:stdio, :line), stderr_to_stdout: true)

    status
  end

  defp raise_no_runtime do
    raise """
    dds needs a runtime. Any of:
      - add {:pythonx, "~> 0.4"} to your deps (recommended — hermetic:
        mix deps.get is the only prerequisite)
      - uv on PATH (https://docs.astral.sh/uv/)
      - python3 >= 3.9 on PATH (stdlib legs only, unless tree-sitter +
        tree-sitter-elixir are importable)
    """
  end
end