/**
 * Group digits.
 */
type GroupDigits = string;

/**
 * Group place.
 */
export type GroupPlace = bigint;

/**
 * Group of digits and its place.
 *
 * The place refers to the order which the digits are grouped, e.g. for a number like
 *
 *   1,234,567
 *
 * The groups would be:
 *
 *   ['001', 2]
 *   ['234', 1]
 *   ['567', 0]
 *
 * Note that groups do not necessarily have the same length of digits, such in the case of
 * South Asian numbering system:
 *
 *   1,00,00,000
 *
 * The groups would be:
 *
 *   ['01', 3]
 *   ['00', 2]
 *   ['00', 1]
 *   ['000', 0]
 */
export type Group = [GroupDigits, GroupPlace];

/**
 * Index of the group digits in a {@link Group|group}.
 */
export const GROUP_DIGITS_INDEX = 0 as const;

/**
 * Index of the group place in a {@link Group|group}.
 */
export const GROUP_PLACE_INDEX = 1 as const;

/**
 * System for stringifying and parsing numbers.
 */
export interface NumberNameSystem {
	/**
	 * Creates a negative string.
	 * @param s - The string to make negative.
	 * @returns string The negative string.
	 */
	makeNegative: (s: string) => string;
	/**
	 * Splits a string into groups.
	 * @param value - The string to group.
	 * @see {NumberNameSystem.combineGroups}
	 * @returns Group[] The groups.
	 */
	splitIntoGroups: (value: string) => Group[];
	/**
	 * Creates a group string.
	 * @param groups - The groups.
	 * @param options - Options to use when creating the group.
	 * @see {NumberNameSystem.parseGroups}
	 * @returns string[] The groups represented into strings.
	 */
	stringifyGroups: <T extends object>(groups: Group[], options?: T) => string[];
	/**
	 * Merges tokens from stringified groups to a string.
	 * @param tokens - The tokens to finalize.
	 * @see {NumberNameSystem.tokenize}
	 * @returns string The merged tokens.
	 */
	mergeTokens: <T extends object>(tokens: string[], options?: T) => string;
	/**
	 * Tokenizes a string.
	 * @param value - The string to tokenize.
	 * @see {NumberNameSystem.mergeTokens}
	 * @returns string[] The tokens.
	 */
	tokenize: (value: string) => string[];
	/**
	 * Parses groups from a string.
	 * @param tokens - The string to parse groups from.
	 * @see {NumberNameSystem.stringifyGroups}
	 * @returns Group[] The parsed groups.
	 */
	parseGroups: (tokens: string[]) => Group[];
	/**
	 * Combines groups into a string.
	 * @param groups - The groups to combine.
	 * @see {NumberNameSystem.splitIntoGroups}
	 * @returns string The combined groups in exponential form.
	 */
	combineGroups: (groups: Group[]) => string;
}

/**
 * Error thrown when an invalid token is encountered.
 */
export class InvalidTokenError extends Error {
	constructor(token: string) {
		super(`Invalid token: ${token}`);
	}
}