#!/usr/bin/env python3
# -*- coding: utf-8 -*-
"""从设备树复算 gpio-in-N 对应的全局 GPIO 号。"""

from pathlib import Path

from .config import DEVICETREE_BASE


def _read_be32(path: Path, offset: int = 0):
    try:
        data = path.read_bytes()
    except OSError:
        return None
    if len(data) < offset + 4:
        return None
    return int.from_bytes(data[offset:offset + 4], "big")


def derive_gpio(n: int, base_dir: str = DEVICETREE_BASE):
    """从设备树复算 IN<n> 的全局 GPIO 号。

    返回 (gpio_num, label, pin) 或 None。
    """
    base = Path(base_dir)
    f = base / f"gpio-in-{n}" / "control-gpios"
    if not f.exists():
        return None

    try:
        data = f.read_bytes()
    except OSError:
        return None
    if len(data) < 8:
        return None

    ph = int.from_bytes(data[0:4], "big")
    pin = int.from_bytes(data[4:8], "big")

    # phandle -> gpio-controller 节点
    ctrl = None
    for c in base.glob("gpio@*/gpio-controller@*"):
        cph = _read_be32(c / "phandle")
        if cph == ph:
            ctrl = c
            break
    if ctrl is None:
        return None

    bank = ctrl.parent.name
    if bank.startswith("gpio@"):
        bank = bank[len("gpio@"):]
    label = f"{bank}.gpio"

    # label -> gpiochip base
    gpio_class = Path("/sys/class/gpio")
    if not gpio_class.exists():
        return None
    for g in gpio_class.glob("gpiochip*"):
        try:
            if (g / "label").read_text().strip() == label:
                chip_base = int((g / "base").read_text().strip())
                return chip_base + pin, label, pin
        except (OSError, ValueError):
            continue
    return None