#!/usr/bin/env python3
"""Pack the bundled binaries into the boot capsule (boot/system.img) — the
single file the EFI loader reads in one sequential pass, which is the only
shape firmware file I/O is fast at (a per-file tree walk measured minutes on
real firmware). The format is the v2 initial_ramdisk (system/initial-ramdisk.zig):
entries named by full FHS path, so the running system is identical whether the
loader read the capsule or walked the tree.

Usage: pack-system-image.py <out.img> [<path> <file>]...
Layout (little-endian): Header{magic "DNR2", count}, Entry{name[64], offset, len}*N, blobs.
"""
import struct
import sys

MAGIC = 0x32524E44  # "DNR2"
HEADER = struct.Struct("<II")
ENTRY = struct.Struct("<64sQQ")


def main() -> int:
    out_path = sys.argv[1]
    rest = sys.argv[2:]
    if len(rest) % 2 != 0:
        sys.stderr.write("usage: pack-system-image.py <out.img> [<path> <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 = []
    offset = table_end
    for path, source in items:
        name = path if path.startswith("/") else "/" + path
        encoded = name.encode("ascii")
        if len(encoded) > 63:
            sys.stderr.write(f"pack-system-image: path too long (>63): {name}\n")
            return 2
        with open(source, "rb") as f:
            data = f.read()
        entries += ENTRY.pack(encoded, offset, len(data))
        blobs.append(data)
        offset += len(data)

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


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