"""Prepare the known-working lwIP component layout for ESP-IDF v6.0.2."""
import filecmp
from pathlib import Path
import shutil
import sys


def replace_once(text, old, new, label):
    if text.count(old) != 1:
        raise RuntimeError(f"Unexpected {label}; expected ESP-IDF v6.0.2 sources")
    return text.replace(old, new, 1)


def write_changed(path, data):
    path.parent.mkdir(parents=True, exist_ok=True)
    if not path.exists() or path.read_bytes() != data:
        path.write_bytes(data)


def prepare(source, destination, arp):
    source, destination, arp = source.resolve(), destination.resolve(), arp.resolve()
    if not arp.is_file():
        raise RuntimeError(f"Missing modified ARP source: {arp}")
    if source == destination or source in destination.parents or destination in source.parents:
        raise RuntimeError("Source and generated directories must be separate")
    if any(c in arp.as_posix() for c in ('"', ';', '$')):
        raise RuntimeError("ARP path contains characters that require CMake escaping")

    cmake = (source / "CMakeLists.txt").read_text()
    cmake = replace_once(cmake, '"lwip/src/core/ipv4/etharp.c"',
                         f'"{arp.as_posix()}"', "lwIP CMakeLists.txt")
    cmake = replace_once(cmake,
                         'if(NOT ${target} STREQUAL "linux")\n    set(priv_requires vfs)\nendif()',
                         'set(priv_requires)\n\nif(NOT ${target} STREQUAL "linux")\n    list(APPEND priv_requires vfs)\nendif()',
                         "lwIP dependencies")
    sockets_path = "lwip/src/include/lwip/sockets.h"
    sockets = (source / sockets_path).read_text()
    if "#ifndef SIOCATMARK" not in sockets:
        line = "#define SIOCATMARK  _IOR('s',  7, unsigned long)  /* at oob mark? */"
        sockets = replace_once(sockets, line, "#endif\n#ifndef SIOCATMARK\n" + line,
                               "SIOCATMARK definition")
    fcntl_path = "port/linux/include/sys/fcntl.h"
    fcntl = (source / fcntl_path).read_text()
    if "#define F_GETFD" not in fcntl:
        fcntl = fcntl.rstrip("\n") + "\n\n#ifndef F_GETFD\n#define F_GETFD 1\n#endif\n"
    changed = {"CMakeLists.txt": cmake.encode(), sockets_path: sockets.encode(),
               fcntl_path: fcntl.encode()}

    # Validate all substitutions before writing. Do not copy or compile stock ARP.
    destination.mkdir(parents=True, exist_ok=True)
    for path in source.rglob("*"):
        relative = path.relative_to(source)
        if ".git" in relative.parts or not path.is_file():
            continue
        name = relative.as_posix()
        if name in changed or name == "lwip/src/core/ipv4/etharp.c":
            continue
        target = destination / relative
        target.parent.mkdir(parents=True, exist_ok=True)
        if not target.is_file() or not filecmp.cmp(path, target, shallow=False):
            shutil.copy2(path, target)
    for name, data in changed.items():
        write_changed(destination / name, data)
    stock_arp = destination / "lwip/src/core/ipv4/etharp.c"
    if stock_arp.exists():
        stock_arp.unlink()


if __name__ == "__main__":
    try:
        if len(sys.argv) != 4:
            raise RuntimeError("Usage: prepare.py SDK_LWIP BUILD_LWIP PATCHED_ETHARP")
        prepare(*(Path(value) for value in sys.argv[1:]))
    except (OSError, RuntimeError) as error:
        sys.exit(str(error))