"""Helpers for assigning stable, collision-free output filenames."""

import os
from typing import Dict, Optional


def resolve_name(name: str, content: bytes, seen: Dict[str, bytes]) -> Optional[str]:
    """Return a unique name, or None when the same name and content were seen.

    Name collisions with different content receive numeric suffixes before
    the extension, while exact duplicates are omitted.
    """
    if name not in seen:
        seen[name] = content
        return name
    if seen[name] == content:
        return None

    base, ext = os.path.splitext(name)
    index = 2
    while f"{base}_{index}{ext}" in seen:
        index += 1
    resolved = f"{base}_{index}{ext}"
    seen[resolved] = content
    return resolved