neiam /gitgud

defmodule GitGud.Git.Nif do
  @moduledoc """
  gitoxide-backed git backend via Rustler.

  The Rust crate at `native/gitgud_gix` provides the actual NIFs. The
  stubs below are replaced at load time by Rustler with the real
  implementations from `native/gitgud_gix/src/lib.rs`.

  Not every operation has a gix implementation yet — see the module
  source. The facade `GitGud.Git` does NOT auto-fall back per-call; if
  the NIF backend is selected but a specific NIF returns
  `{:error, :unsupported}`, the caller is expected to handle it (and
  in practice the facade routes through one backend at a time).
  """
  @behaviour GitGud.Git.Backend

  use Rustler, otp_app: :git_gud, crate: "gitgud_gix"

  # The functions below act as stubs the NIF overrides at load time.
  # If the NIF fails to load, calling them raises :nif_not_loaded —
  # which `Git.pick_backend/0` avoids by gating on `available?/0`.

  def nif_loaded, do: false

  @impl true
  def available?, do: function_exported?(__MODULE__, :nif_loaded, 0) and nif_loaded()

  @impl true
  def init_bare(_path), do: nif_error()

  @impl true
  def list_refs(_path), do: nif_error()

  @impl true
  def log(_path, _start_sha, _opts), do: nif_error()

  @impl true
  def commit(_path, _sha), do: nif_error()

  @impl true
  def tree(_path, _sha), do: nif_error()

  @impl true
  def blob_bytes(_path, _sha), do: nif_error()

  @impl true
  def blob_meta(_path, _sha), do: nif_error()

  @impl true
  def diff_stats(_path, _base, _head), do: nif_error()

  @impl true
  def diff(_path, _base, _head, _opts), do: {:error, :unsupported}

  @impl true
  def resolve(_path, _ref_or_sha), do: nif_error()

  @impl true
  def merge_base(_path, _a, _b), do: nif_error()

  @impl true
  def merge_tree(_path, _base, _a, _b), do: nif_error()

  @impl true
  def commit_tree(_path, _tree_sha, _parents, _message, _opts), do: nif_error()

  @impl true
  def update_ref(_path, _ref, _new_sha, _expected_old), do: nif_error()

  defp nif_error, do: :erlang.nif_error(:nif_not_loaded)
end