"""跨平台非阻塞键盘读取。

Windows 用 ``msvcrt``，POSIX 用 ``termios`` + ``select``，
两端统一返回规范化的按键名，TUI 层无需关心平台差异。

在非交互式环境（管道、重定向）下 ``available`` 为 False，
TUI 会退化为无输入的只读模式。
"""

from __future__ import annotations

import os
import sys

IS_WINDOWS = os.name == "nt"

# Windows 下的扩展键（以 \x00 / \xe0 开头）
_WIN_EXTENDED = {
    "H": "UP",
    "P": "DOWN",
    "K": "LEFT",
    "M": "RIGHT",
    "G": "HOME",
    "O": "END",
    "S": "DELETE",
}

_WIN_CTRL = {
    "\x03": "CTRL_C",
    "\r": "ENTER",
    "\n": "ENTER",
    "\t": "TAB",
    "\x08": "BACKSPACE",
    "\x1b": "ESC",
    " ": "SPACE",
}


class KeyReader:
    """把终端的原始字节流转换成按键名。"""

    def __init__(self) -> None:
        self.available = sys.stdin is not None and sys.stdin.isatty()
        self._fd: int | None = None
        self._saved_term = None

        if self.available and not IS_WINDOWS:
            try:
                import termios
                import tty

                self._fd = sys.stdin.fileno()
                self._saved_term = termios.tcgetattr(self._fd)
                # cbreak: 立即返回按键，但保留 Ctrl-C 等信号
                tty.setcbreak(self._fd)
            except Exception:
                self.available = False
                self._saved_term = None

        if self.available and IS_WINDOWS:
            try:
                import msvcrt  # noqa: F401
            except Exception:
                self.available = False

    # ------------------------------------------------------------------ 读取
    def poll(self) -> str | None:
        """非阻塞读取一个按键；没有按键时返回 None。"""
        if not self.available:
            return None
        return self._poll_windows() if IS_WINDOWS else self._poll_posix()

    def _poll_windows(self) -> str | None:
        import msvcrt

        if not msvcrt.kbhit():
            return None
        char = msvcrt.getwch()

        if char in ("\x00", "\xe0"):
            if not msvcrt.kbhit():
                return None
            return _WIN_EXTENDED.get(msvcrt.getwch().upper())
        if char in _WIN_CTRL:
            return _WIN_CTRL[char]
        return char.lower()

    def _poll_posix(self) -> str | None:
        import select

        if self._fd is None:
            return None
        try:
            ready, _, _ = select.select([self._fd], [], [], 0)
        except (OSError, ValueError):
            return None
        if not ready:
            return None
        try:
            data = os.read(self._fd, 8)
        except OSError:
            return None
        if not data:
            return None

        text = data.decode("utf-8", errors="ignore")
        if not text:
            return None

        # 方向键：ESC [ A/B/C/D，或 ESC O A/B/C/D
        if text.startswith("\x1b["):
            return {"A": "UP", "B": "DOWN", "C": "RIGHT", "D": "LEFT"}.get(text[2:3])
        if text.startswith("\x1bO"):
            return {"A": "UP", "B": "DOWN", "C": "RIGHT", "D": "LEFT"}.get(text[2:3])

        char = text[0]
        mapping = {
            "\x03": "CTRL_C",
            "\r": "ENTER",
            "\n": "ENTER",
            "\t": "TAB",
            "\x7f": "BACKSPACE",
            "\x08": "BACKSPACE",
            "\x1b": "ESC",
            " ": "SPACE",
        }
        if char in mapping:
            return mapping[char]
        return char.lower()

    # ------------------------------------------------------------------ 清理
    def close(self) -> None:
        if self._fd is not None and self._saved_term is not None:
            try:
                import termios

                termios.tcsetattr(self._fd, termios.TCSADRAIN, self._saved_term)
            except Exception:
                pass
        self._fd = None
        self._saved_term = None