"""Transports: how agentd reaches a terminal's machine (files, detached launch, kill).

Interface (duck-typed, see docs/executor-contract.md):
  os, join(*parts), quote(s), default_run_root()
  mkdir(path, clean=False), write_text(path, text), read_text(path) -> str|None,
  grep_first(path, needle) -> str|None, tail(path, n) -> str
  runner(run_dir, cwd, command, stdout_name) -> (script_name, script_text)
  launch(task, script_path, run_dir), kill(task, run_dir), forget(task)
  process_count(name) -> int|None (None = unreachable)"""


class TransportError(Exception):
    pass


def make_transport(cfg, terminal):
    kind = cfg.terminals[terminal]["transport"]
    if kind == "local":
        from .local import LocalTransport
        return LocalTransport(cfg, terminal)
    if kind == "warpgate-ssh":
        from .warpgate_ssh import WarpgateSshTransport
        return WarpgateSshTransport(cfg, terminal)
    raise TransportError("unknown transport %s" % kind)