"""Nova client-mode resolver (P1, REQ-327, D-226).

Priority: --mode flag → NOVA_CLIENT_MODE env → credential type → TTY.
No silent fallbacks: every return carries a non-empty selection_reason.

INV-13: invalid env values are ignored + warned, then fall through.
INV-14: credential_type developer_pat/nova_oidc_token + TTY →
interactive; + no-TTY → agent. TTY check is sys.stdin.isatty() (D-226).
"""

from __future__ import annotations

import json
import logging
import os
import sys
from pathlib import Path
from typing import Optional, Tuple

log = logging.getLogger("nova.mode_resolver")

_VALID_MODES = ("agent", "interactive")
_CRED_MODE_TYPES = ("developer_pat", "nova_oidc_token")


def resolve_mode(
    flag: Optional[str] = None,
    env_var: Optional[str] = None,
    credential_type: Optional[str] = None,
    stdin_isatty: bool = False,
) -> Tuple[str, str]:
    """Return (mode, selection_reason) honoring D-226 priority."""
    if flag is not None and flag in _VALID_MODES:
        return flag, "flag"
    if env_var is not None and env_var != "":
        if env_var in _VALID_MODES:
            return env_var, "env"
        log.warning(
            "NOVA_CLIENT_MODE=%r invalid (expected one of %s); ignoring",
            env_var,
            _VALID_MODES,
        )
    if credential_type in _CRED_MODE_TYPES:
        mode = "interactive" if stdin_isatty else "agent"
        return mode, f"credential:{credential_type}"
    mode = "interactive" if stdin_isatty else "agent"
    return mode, "tty"


def _read_credential_type(path: Path) -> Optional[str]:
    """Read the active credential's type from ~/.nova/credentials.json."""
    try:
        data = json.loads(path.read_text())
    except (OSError, json.JSONDecodeError):
        return None
    active_jti = data.get("active_credential_jti")
    for cred in data.get("credentials", []) or []:
        if cred.get("jti") == active_jti:
            return cred.get("type")
    return None


def resolve_mode_from_env(credential_type: Optional[str] = None) -> Tuple[str, str]:
    """Resolve mode using sys.argv, NOVA_CLIENT_MODE, credentials, and TTY.

    Best-effort --mode scan of sys.argv (no full argparse); env var;
    ~/.nova/credentials.json active credential type; sys.stdin.isatty().
    """
    flag: Optional[str] = None
    argv = sys.argv[1:]
    for i, tok in enumerate(argv):
        if tok == "--mode" and i + 1 < len(argv):
            flag = argv[i + 1]
            break
        if tok.startswith("--mode="):
            flag = tok.split("=", 1)[1]
            break
    env_var = os.environ.get("NOVA_CLIENT_MODE")
    if env_var is not None and env_var == "":
        env_var = ""
    if credential_type is None:
        cred_path = Path.home() / ".nova" / "credentials.json"
        credential_type = _read_credential_type(cred_path)
    return resolve_mode(
        flag=flag,
        env_var=env_var,
        credential_type=credential_type,
        stdin_isatty=sys.stdin.isatty(),
    )


if __name__ == "__main__":
    mode, reason = resolve_mode_from_env()
    print(f"mode={mode} reason={reason}")