/**
 * Sanitizes a FormData value by key, returning a trimmed string.
 * If the key is not present, it throws an error or returns a fallback value.
 * @param data - The FormData object to sanitize.
 * @param key - The key to look for in the FormData.
 * @param fallback - Optional fallback value to return if the key is not found.
 * @returns The sanitized string value or the fallback value.
 * @throws Error if the key is required and not found.
 * @template Fallback - The type of the fallback value.
 */
export function sanitize(data: FormData, key: string): string;
export function sanitize<Fallback>(
	data: FormData,
	key: string,
	fallback: Fallback
): string | Fallback;
export function sanitize<Fallback>(
	data: FormData,
	key: string,
	fallback?: Fallback
): string | Fallback {
	const val = data.get(key);
	if (val !== null) return val.toString().trim();

	if (fallback !== undefined) return fallback;
	throw new Error(`Missing required field: ${key}`);
}