from __future__ import annotations

from pathlib import Path


def discover_videos(
    input_dir: str | Path,
    extensions: list[str],
    *,
    recursive: bool,
) -> list[Path]:
    root = Path(input_dir).expanduser()
    if not root.exists():
        raise FileNotFoundError(f"input dir not found: {root}")
    if not root.is_dir():
        raise NotADirectoryError(f"input path is not a directory: {root}")

    allowed = {
        extension.lower() if extension.startswith(".") else f".{extension.lower()}"
        for extension in extensions
    }
    iterator = root.rglob("*") if recursive else root.iterdir()
    return sorted(
        path
        for path in iterator
        if path.is_file() and path.suffix.lower() in allowed
    )