#!/usr/bin/env python3
"""Turn a Quartus .ttf bitstream into the app image embedded in a MKR Vidor 4000 sketch.

The Vidor bootloader expects the bitstream bytes bit-reversed relative to Quartus' .ttf
output, written as a C initializer list (bitstream.h), plus a signature block (signature.h)
describing where the image goes in the FPGA's flash. The app image slot starts at 512 KB.
"""

import argparse
import hashlib
from pathlib import Path

APP_OFFSET_KB = 512
IMAGE_TYPE_APP = 1


def reverse_bits(byte: int) -> int:
    return int(f"{byte:08b}"[::-1], 2)


def read_ttf(path: Path) -> bytes:
    values = (field.strip() for field in path.read_text().split(","))
    return bytes(reverse_bits(int(v)) for v in values if v)


def format_initializer(data: bytes) -> str:
    lines = []
    for start in range(0, len(data), 16):
        chunk = data[start:start + 16]
        if len(chunk) == 16:
            lines.append(", ".join(f"{b:3d}" for b in chunk) + ",")
        else:
            lines.append("".join(f"{b:3d}, " for b in chunk))
    return "\n".join(lines) + "\n"


def hex_bytes(data: bytes) -> str:
    return ", ".join(f"0x{b:02x}" for b in data) + ","


def format_signature(image_text: str, length: int) -> str:
    digest = hashlib.sha256(image_text.encode()).digest()
    return "\n".join([
        "NO_BOOTLOADER,",
        hex_bytes((APP_OFFSET_KB * 1024).to_bytes(4, "little")),
        hex_bytes(length.to_bytes(4, "little")),
        hex_bytes(digest),
        hex_bytes(IMAGE_TYPE_APP.to_bytes(4, "little")),
        "0x00, 0x00, 0x00, 0x00, // force flag",
        "NO_USER_DATA,",
    ]) + "\n"


def main() -> None:
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument("ttf", type=Path, help="Quartus .ttf bitstream")
    parser.add_argument("out_dir", type=Path, help="directory for bitstream.h and signature.h")
    args = parser.parse_args()

    data = read_ttf(args.ttf)
    image_text = format_initializer(data)
    args.out_dir.mkdir(parents=True, exist_ok=True)
    (args.out_dir / "bitstream.h").write_text(image_text)
    (args.out_dir / "signature.h").write_text(format_signature(image_text, len(data)))
    print(f"{len(data)} bytes -> {args.out_dir}/bitstream.h, signature.h")


if __name__ == "__main__":
    main()