"""Utilities"""

import re


def letters_only(s: str) -> str:
    return re.compile('[^a-zA-Z]').sub('', s)


def words_only(s: str) -> str:
    words = [letters_only(x) for x in s.split()]
    r = []
    for w in words:
        if w:
            r.append(w)
    return ' '.join(r)


def file_name(s: str, ext='txt') -> str:
    return '%s.%s' % (s.lower().replace(' ', '_'), ext)


def dedupe(strings: list[str]) -> list[str]:
    seen = set()
    r = []
    for s in strings:
        if s not in seen:
            r.append(s)
            seen.add(s)
    return r


def header(s: str) -> str:
    return words_only(s).lower().title()