import type { MaskRule } from "../types/mask-types.js";

/**
 * Phone-number masking strategy.
 *
 * Keeps the last 4 digits of a phone number and replaces all preceding digit
 * positions with `*`, while preserving non-digit separator characters
 * (hyphens, spaces, parentheses, dots, `+`) so the output remains formatted
 * consistently with the input.
 *
 * Example: `+1-555-123-4567` → `*-***-***-4567`
 *
 * @param value - The original phone number string.
 * @param rule  - The `MaskRule` (not consumed by this strategy).
 * @returns The masked phone number.
 */
export function maskPhone(value: string, rule: MaskRule): string {
    void rule;
    // Extract only the digit characters to determine the last-4 boundary.
    const digits = value.replace(/\D/g, "");
    if (digits.length === 0) return value;

    const keepFrom = Math.max(0, digits.length - 4);
    // Walk the original string, replacing digits that are NOT in the last 4.
    let digitsSeen = 0;
    let result = "";
    for (const ch of value) {
        if (/\d/.test(ch)) {
            if (digitsSeen < keepFrom) {
                result += "*";
            } else {
                result += ch;
            }
            digitsSeen++;
        } else {
            result += ch;
        }
    }
    return result;
}