"""Find every class whose constant pool references a named method.

Used to answer "who actually calls this" across a whole jar, where grepping
source would only show the decompiled view and javap would need one command per
class.

    python find_callers.py <classes-dir> <method-name>
"""

import os
import struct
import sys

sys.path.insert(0, os.path.dirname(os.path.abspath(__file__)))
from struct_diff import Reader, read_constant_pool, CONSTANT_UTF8, SKIP_TWO_SLOT


def method_names(path):
    with open(path, 'rb') as handle:
        data = handle.read()
    reader = Reader(data)
    if reader.u4() != 0xCAFEBABE:
        return None
    reader.u2()
    reader.u2()
    pool = read_constant_pool(reader)
    names = []
    for index, entry in enumerate(pool):
        if isinstance(entry, str):
            names.append(entry)
    return names


def main():
    root, needle = sys.argv[1], sys.argv[2]
    hits = []
    for base, _dirs, files in os.walk(root):
        for name in files:
            if not name.endswith('.class'):
                continue
            full = os.path.join(base, name)
            key = os.path.relpath(full, root).replace(os.sep, '/')
            try:
                names = method_names(full)
            except Exception:
                continue
            if names is None:
                continue
            if any(n == needle or n.startswith(needle) for n in names):
                hits.append(key)
    print('%d class(es) reference %s' % (len(hits), needle))
    for key in hits:
        print('  %s' % key)


if __name__ == '__main__':
    main()