#!/usr/bin/env python3

"""Convert an image to an uncompressed LVGL RGB565 launcher background."""

import argparse
import shutil
import struct
import subprocess
from pathlib import Path


LV_IMAGE_HEADER_MAGIC = 0x19
LV_COLOR_FORMAT_RGB565 = 0x12


def parse_args() -> argparse.Namespace:
    parser = argparse.ArgumentParser(
        description=(
            "Create an uncompressed LVGL .bin image for "
            "/sdcard/tactility/launcher/background.bin"
        )
    )
    parser.add_argument("input", type=Path, help="Source image")
    parser.add_argument("output", type=Path, help="Destination .bin file")
    parser.add_argument("--width", type=int, required=True, help="Output width")
    parser.add_argument("--height", type=int, required=True, help="Output height")
    return parser.parse_args()


def main() -> None:
    args = parse_args()
    if args.width <= 0 or args.width > 65535 or args.height <= 0 or args.height > 65535:
        raise SystemExit("width and height must be between 1 and 65535")

    magick = shutil.which("magick")
    if magick is None:
        raise SystemExit("ImageMagick is required (the 'magick' command was not found)")

    command = [
        magick,
        str(args.input),
        "-resize",
        f"{args.width}x{args.height}^",
        "-gravity",
        "center",
        "-extent",
        f"{args.width}x{args.height}",
        "-depth",
        "8",
        "rgb:-",
    ]
    rgb888 = subprocess.run(command, check=True, stdout=subprocess.PIPE).stdout
    expected_size = args.width * args.height * 3
    if len(rgb888) != expected_size:
        raise SystemExit(f"unexpected ImageMagick output: {len(rgb888)} bytes, expected {expected_size}")

    rgb565 = bytearray(args.width * args.height * 2)
    for source_offset in range(0, len(rgb888), 3):
        r, g, b = rgb888[source_offset : source_offset + 3]
        pixel = ((r >> 3) << 11) | ((g >> 2) << 5) | (b >> 3)
        destination_offset = (source_offset // 3) * 2
        struct.pack_into("<H", rgb565, destination_offset, pixel)

    stride = args.width * 2
    header = struct.pack(
        "<BBHHHHH",
        LV_IMAGE_HEADER_MAGIC,
        LV_COLOR_FORMAT_RGB565,
        0,
        args.width,
        args.height,
        stride,
        0,
    )

    args.output.parent.mkdir(parents=True, exist_ok=True)
    args.output.write_bytes(header + rgb565)
    print(
        f"Wrote {args.output} ({args.width}x{args.height}, "
        f"{len(header) + len(rgb565)} bytes, uncompressed RGB565)"
    )


if __name__ == "__main__":
    main()