"""Session-level interaction state. No domain, so it lives in core (D-263).

One question, asked in one place: **may this invocation prompt?**

The answer is not just a flag, because the flag alone is not safe. A prompt with
no TTY does not wait for an answer — it *crashes*, which is the recorded `tea`
failure in this repo (interactive prompts die in Claude Code, no terminal). So
`can_prompt()` requires both an interactive stream and the absence of
`--no-input`. Hooks and agents pass `--no-input` explicitly, and would be
protected by the TTY check even if they forgot.

Nothing prompts today. This exists so that the first thing that wants to has an
obvious correct answer available, rather than inventing its own `isatty` check
that gets it half right.
"""

from __future__ import annotations

import sys

_no_input = False


def set_no_input(value: bool) -> None:
    """Record the `--no-input` flag for this invocation."""
    global _no_input
    _no_input = value


def no_input() -> bool:
    """True when the caller has forbidden prompting."""
    return _no_input


def can_prompt() -> bool:
    """True only when prompting is both permitted AND possible.

    Check this, never `isatty` alone and never the flag alone — the two guard
    different failures. The flag is a caller's instruction; the TTY check is
    what stops a prompt from crashing a hook that forgot to pass it.
    """
    if _no_input:
        return False
    try:
        return sys.stdin.isatty() and sys.stderr.isatty()
    except (AttributeError, ValueError):
        return False