#!/usr/bin/env python3
"""Removes MethodParameters attributes from .class files (in place).

JDK 21+ javac always emits them for inner-class constructors, and older d8 releases
crash on the nameless ones. They are only reflection metadata, so dropping them is safe.
usage: strip_method_params.py file.class...
"""
import struct
import sys


def strip(path):
    d = open(path, "rb").read()
    n = struct.unpack(">H", d[8:10])[0]
    p, i, utf8 = 10, 1, {}
    while i < n:
        t = d[p]
        if t == 1:
            ln = struct.unpack(">H", d[p + 1:p + 3])[0]
            utf8[i] = d[p + 3:p + 3 + ln]
            p += 3 + ln
        elif t in (3, 4, 9, 10, 11, 12, 17, 18):
            p += 5
        elif t in (5, 6):
            p += 9
            i += 1
        elif t in (7, 8, 16, 19, 20):
            p += 3
        elif t == 15:
            p += 4
        else:
            raise ValueError("bad constant tag %d in %s" % (t, path))
        i += 1
    out = bytearray(d[:p])
    p_access = p
    ifaces = struct.unpack(">H", d[p + 6:p + 8])[0]
    p += 8 + 2 * ifaces
    out += d[p_access:p]

    def members(p, drop):
        count = struct.unpack(">H", d[p:p + 2])[0]
        buf = bytearray(d[p:p + 2])
        p += 2
        for _ in range(count):
            buf += d[p:p + 6]
            acount = struct.unpack(">H", d[p + 6:p + 8])[0]
            p += 8
            kept = []
            for _ in range(acount):
                name, ln = struct.unpack(">HI", d[p:p + 6])
                if utf8.get(name) != drop:
                    kept.append(d[p:p + 6 + ln])
                p += 6 + ln
            buf += struct.pack(">H", len(kept)) + b"".join(kept)
        return p, buf

    p, fields = members(p, None)
    out += fields
    p, methods = members(p, b"MethodParameters")
    out += methods
    out += d[p:]
    if bytes(out) != d:
        open(path, "wb").write(bytes(out))
        return 1
    return 0


changed = sum(strip(f) for f in sys.argv[1:])
print("stripped MethodParameters from %d class files" % changed)