#!/usr/bin/env python3
"""Build-time initial_ramdisk packer. Concatenates user binaries into one image the
bootloader ferries to the kernel.

Usage: make-initial-ramdisk.py <out.img> [<name> <file>]...

Image layout (little-endian), mirroring src/user/proto/initial-ramdisk.zig:
    Header   : magic u32 ("DNRD"=0x444E5244), count u32
    Entry*N  : name [32]u8 (NUL-padded), offset u64, len u64
    blobs    : each entry's file bytes at its offset
"""
import struct
import sys

MAGIC = 0x444E5244
HEADER = struct.Struct("<II")     # magic, count
ENTRY = struct.Struct("<32sQQ")   # name[32], offset, len


def main() -> int:
    out_path = sys.argv[1]
    rest = sys.argv[2:]
    if len(rest) % 2 != 0:
        sys.stderr.write("usage: make-initial-ramdisk.py <out.img> [<name> <file>]...\n")
        return 2
    items = [(rest[i], rest[i + 1]) for i in range(0, len(rest), 2)]

    table_end = HEADER.size + len(items) * ENTRY.size
    entries = b""
    blobs = []
    off = table_end
    for name, path in items:
        with open(path, "rb") as f:
            data = f.read()
        entries += ENTRY.pack(name.encode()[:31], off, len(data))
        blobs.append(data)
        off += len(data)

    with open(out_path, "wb") as f:
        f.write(HEADER.pack(MAGIC, len(items)))
        f.write(entries)
        for b in blobs:
            f.write(b)
    return 0


if __name__ == "__main__":
    sys.exit(main())