feat: add jest and initial tests for masking values

utils/maskValue.ts

@@ -1,15 +1,44 @@
-const emailRegex =
-  /(?<=.)[^@\n](?=[^@\n]*?@)|(?:(?<=@.+)|(?!^)\G(?=[^@\n]*$)).(?=.*\.)/gm
+function maskAllButFirstChar(str: string) {
+  const first = str[0]
+  const rest = str.substring(1)
+  const restMasked = "*".repeat(rest.length)
+
+  return `${first}${restMasked}`
+}
+
+function maskAllButLastTwoChar(str: string) {
+  const lastTwo = str.slice(-2)
+  const rest = str.substring(0, str.length - 2)
+  const restMasked = "*".repeat(rest.length)
+
+  return `${restMasked}${lastTwo}`
+}
+
 export function email(str: string) {
-  return str.replace(emailRegex, "*")
+  const parts = str.split("@")
+
+  const aliasMasked = maskAllButFirstChar(parts[0])
+
+  if (parts[1]) {
+    const domainParts = parts[1].split(".")
+    if (domainParts.length > 1) {
+      const domainTLD = domainParts.pop()
+      const domainPartsMasked = domainParts
+        .map((domainPart, i) => {
+          return maskAllButFirstChar(domainPart)
+        })
+        .join(".")
+      return `${aliasMasked}@${domainPartsMasked}.${domainTLD}`
+    }
+  }
+
+  return maskAllButFirstChar(str)
 }
 
-const phoneRegex = /.(?!.{0,1}$)/gm
 export function phone(str: string) {
-  return str.replace(phoneRegex, "*")
+  return maskAllButLastTwoChar(str)
 }
 
-const textRegex = /(?!^)./gm
 export function text(str: string) {
-  return str.replace(textRegex, "*")
+  return maskAllButFirstChar(str)
 }

utils/maskvalue.test.ts

@@ -0,0 +1,22 @@
+import { describe, expect, test } from "@jest/globals"
+
+import { email, phone, text } from "./maskValue"
+
+describe("Mask value", () => {
+  test("masks e-mails properly", () => {
+    expect(email("test@example.com")).toBe("t***@e******.com")
+    expect(email("test@sub.example.com")).toBe("t***@s**.e******.com")
+    expect(email("test_no_atexample.com")).toBe("t********************")
+    expect(email("test_no_dot@examplecom")).toBe("t*********************")
+    expect(email("test_no_at_no_dot_com")).toBe("t********************")
+  })
+
+  test("masks phone number properly", () => {
+    expect(phone("0000000000")).toBe("********00")
+  })
+
+  test("masks text strings properly", () => {
+    expect(text("test")).toBe("t***")
+    expect(text("test.with.dot")).toBe("t************")
+  })
+})