"""Find comparisons of a value against itself.

FernFlower sometimes merges two distinct locals into one name, producing
expressions like d1 != d1 that are always false. The compiler accepts them, so
they survive a clean build and silently disable the code around them.

    python find_self_comparisons.py <src-root>
"""

import io
import os
import re
import sys

# a.b() != a.b() and simple locals: word != word, word == word
COMPARISON = re.compile(r'(?<![\w.])([A-Za-z_]\w*(?:\(\))?)\s*(!=|==)\s*\1(?![\w(])')


def main():
    root = sys.argv[1]
    hits = []
    for base, _dirs, files in os.walk(root):
        for name in files:
            if not name.endswith('.java'):
                continue
            path = os.path.join(base, name)
            with io.open(path, encoding='utf-8') as handle:
                for number, line in enumerate(handle, 1):
                    stripped = line.strip()
                    if stripped.startswith('*') or stripped.startswith('//'):
                        continue
                    for match in COMPARISON.finditer(line):
                        hits.append((os.path.relpath(path, root).replace(os.sep, '/'),
                                     number, match.group(0), stripped))

    if not hits:
        print('no self-comparisons found')
        return 0
    print('%d self-comparison(s):' % len(hits))
    for path, number, found, line in hits:
        print('  %s:%d  %s' % (path, number, found))
        print('      %s' % line)
    return 0


if __name__ == '__main__':
    raise SystemExit(main())