"""WS2812 via Pi 5 kernel ws2812-pio driver (/dev/ledsN)."""

from __future__ import annotations

from pathlib import Path


class PioBackend:
    def __init__(self, led_count: int, *, device: str = "/dev/leds0") -> None:
        self._led_count = led_count
        self._device = device
        self._path = Path(device)
        if not self._path.exists():
            raise FileNotFoundError(
                f"{device} not found — enable ws2812-pio in /boot/firmware/config.txt "
                "and reboot. Run: pipenv run python examples/setup_pi5_leds.py"
            )

    @property
    def led_count(self) -> int:
        return self._led_count

    @property
    def device(self) -> str:
        return self._device

    def write_grb(self, grb_bytes: bytes) -> None:
        if len(grb_bytes) != self._led_count * 3:
            raise ValueError(
                f"expected {self._led_count * 3} bytes, got {len(grb_bytes)}"
            )

        # Kernel driver expects RGBW uint32 little-endian per pixel (W=0 for RGB).
        frame = bytearray(self._led_count * 4)
        for i in range(self._led_count):
            base = i * 3
            g, r, b = grb_bytes[base], grb_bytes[base + 1], grb_bytes[base + 2]
            offset = i * 4
            frame[offset] = r
            frame[offset + 1] = g
            frame[offset + 2] = b
            frame[offset + 3] = 0

        with open(self._path, "wb") as dev:
            dev.write(frame)

    def clear(self) -> None:
        with open(self._path, "wb") as dev:
            dev.write(b"\x00" * (self._led_count * 4))

    def close(self) -> None:
        self.clear()

    def __enter__(self) -> PioBackend:
        return self

    def __exit__(self, *_exc) -> None:
        self.close()