kotindia-core/io.github.kotindia/Passport/mask

mask

fun mask(value: String, visibleStart: Int = 0, visibleEnd: Int = 4, maskChar: Char = 'X'): String(source)

Masks a Passport number for PII-safe display.

Passport is Private government ID PII — always mask before displaying in UI or logging.

Masking operates on the raw input string (not normalised). This is intentional — the masker is a display utility that works character-by-character on whatever string it receives. Callers who want to mask a normalised Passport number should call format first: Passport.mask(Passport.format(value)).

Default (visibleStart=0, visibleEnd=4, maskChar='X'): Shows last 4 characters, masks the rest. "M1234567" → "XXXX4567" (last 4: "4567")

Edge cases (all safe — never throws):

Empty input → returns "".
visibleStart + visibleEnd >= value.length → entire string returned unmasked (overlap rule).
Non-normalised input (lowercase, spaces) → masking applied character-by-character on the raw string. No normalisation is performed.

Return

Masked string. Never throws — display-safe by contract.

Parameters

value

Raw Passport number string to mask. No normalisation is applied.

visibleStart

Number of leading characters to show unmasked. Default: 0.

visibleEnd

Number of trailing characters to show unmasked. Default: 4.

maskChar

Character to replace masked positions. Default: 'X'.

Samples

check(Passport.mask("A1234567") == "XXXX4567")