#!/usr/bin/env python
"""
replace stuff in a file or files
"""
import argparse
import difflib
import fileinput
import sys

cli = argparse.ArgumentParser(description=__doc__)
cli.add_argument(
    "-d", "--diff", action="store_true", help="print diffs for every replacement"
)
cli.add_argument("old", type=str, help="target string")
cli.add_argument("new", type=str, help="replacement string")
cli.add_argument(
    "files", nargs="*", metavar="FILE", help="file(s) to operate on, or omit for stdin",
)
args = cli.parse_args()

differ = difflib.Differ()

for line in fileinput.input(files=args.files, inplace=True):
    replacement = line.replace(args.old, args.new)
    if args.diff and args.old in line:
        diff = list(differ.compare([line], [replacement]))
        sys.stderr.write(f"{fileinput.filename()}:{fileinput.lineno()}:\n")
        sys.stderr.writelines(diff)
    print(replacement, end="")