Initial Commit

packages/foundation/data/data-masking/src/strategies/phone.ts

@@ -0,0 +1,40 @@
+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;
+}