Architecture

pt-fiscal is a set of pure functions grouped by domain, with no shared state and no runtime dependencies. Each validator normalizes input, then applies a structural check and a checksum/check-digit.

flowchart LR
  IN["raw input<br/>(NIF / IBAN / CP7)"] --> N["normalize<br/>(strip spaces, PT prefix)"]
  N --> S{"structure ok?"}
  S -- no --> F["false"]
  S -- yes --> C["checksum / check digit<br/>(mod-11 · ISO 7064 mod-97)"]
  C --> R["valid : boolean"]

Module map

Module	Responsibility
nif.ts	NIF normalize, entity-type classification, mod-11 check digit
iban.ts	IBAN normalize, ISO 7064 mod-97 checksum, PT length rule
postal.ts	CP7 format validation & normalization
atcud.ts	Build/validate the document unique code
qrcode.ts	Compose the AT invoice QR field string
index.ts	Public API surface

Design principles

• Pure & deterministic — every function is input → output, safe on client or server.
• Zero runtime dependencies — nothing to audit or update; ships as ESM with types.
• Structure, not existence — validation proves shape and check digits, never that an identifier is assigned/active.
• Composition over bundling — the QR builder returns a string; rendering is your choice (keeps the package dependency-free).