Spanish NIE

What it covers

Returns a valid Spanish NIE (foreigner identity number): an `X`/`Y`/`Z` prefix, 7 digits, and a correct control letter. Set `invalid=true` for a NIE with a deliberately wrong control letter.

How it’s calculated

The NIE control letter is the Spanish DNI mod-23 check character: replace the X/Y/Z prefix with 0/1/2, prepend it to the 7-digit body to form an 8-digit number, take number mod 23, and index the 23-letter alphabet TRWAGMYFPDXBNJZSQVHLCKE.

Prefix Y -> prefixValue = indexOf('Y') in "XYZ" = 1.
Prepend to body 1234567: numeric string = "1" + "1234567" = "11234567", so N = 11234567.
N mod 23: 23 * 488459 = 11234557; 11234567 - 11234557 = 10, so R = 10.
ALPHABET = "TRWAGMYFPDXBNJZSQVHLCKE"; position 10 (0-indexed) = T(0) R(1) W(2) A(3) G(4) M(5) Y(6) F(7) P(8) D(9) X(10) -> 'X'.
Control letter = X.

Edge cases

• The prefix is limited to X, Y, Z. Historically X was assigned first, then Y, and now Z; each maps to substitute digit 0, 1, 2 respectively before the mod-23 computation.
• The generator draws the first body digit in the range 1-9 (no leading zero) for the common shape, though a leading zero is still mathematically valid since the numeric value is what feeds the mod-23 step.

Gotchas

• The check character is a LETTER, not a digit — it is the mod-23 residue mapped through the fixed non-alphabetical alphabet TRWAGMYFPDXBNJZSQVHLCKE, so you cannot just append the remainder as a number.
• The modulus is applied to the full 8-digit number formed AFTER substituting the prefix letter with its digit — you must prepend the 0/1/2 substitute, not run mod-23 on the 7 body digits alone.
• The control alphabet is shared with the DNI; the only NIE-specific step is the X/Y/Z -> 0/1/2 prefix substitution.