# `PiiCatalog.Validators`
[🔗](https://github.com/signalvaultio/pii_catalog/blob/v0.1.0/lib/pii_catalog/validators.ex#L1)

Checks a candidate match must pass before it counts.

A regex finds values of the right shape; many of those are order numbers,
timestamps or version strings. Where an identifier carries a check digit
or a structure the regex cannot express, it is confirmed here.

Each check takes only the matched bytes. It does not depend on the text
around them, so a value gives the same answer wherever it is found.

`valid?/2` takes the name of a check, which is a pattern's `validator`
field, not the pattern's name; several patterns could share one check.
`PiiCatalog.valid?/2` takes a pattern name.

Three checks compare a date of birth with today's date
(`Date.utc_today/0`): `:pesel_pl`, `:isikukood_ee` (a date after today is
refused) and `:rrn_be` (the reading for people born from 2000 is tried
only for a year that has begun). Their answer for a given value can change
as time passes.

# `date?`

```elixir
@spec date?(integer(), integer(), integer()) :: boolean()
```

Whether a day, month and two-digit year can be a date of birth. Without the
century, 29 February is accepted in every year divisible by four.

# `describe`

```elixir
@spec describe(atom() | nil) :: String.t()
```

What a check confirms, in a few words: `"Luhn check digit"`. `nil`, no
check, is `"Format only"`.

# `digits`

```elixir
@spec digits(binary()) :: [0..9]
```

The decimal digits in a value, in order, with separators dropped.

# `iban_length`

```elixir
@spec iban_length(String.t()) :: pos_integer() | nil
```

The IBAN length for a country code, or `nil` outside SEPA.

# `iban_lengths`

```elixir
@spec iban_lengths() :: %{required(String.t()) => pos_integer()}
```

The IBAN length of every country in the EPC's list of SEPA countries, as
a map from the country code to the length: `%{"AD" => 24, ...}`.

# `iso7064_mod11_10`

```elixir
@spec iso7064_mod11_10([0..9]) :: 0..9
```

The ISO 7064 MOD 11,10 check digit for a list of digits. Used by the
German Steuer-ID and the German and Croatian VAT numbers.

# `luhn?`

```elixir
@spec luhn?([0..9]) :: boolean()
```

The Luhn check (ISO/IEC 7812-1), on a list of digits. Used by payment cards,
and by Swedish personnummer on the ten-digit form.

# `mod11_check_digit`

```elixir
@spec mod11_check_digit([0..9], [pos_integer()]) :: 0..9 | nil
```

A weighted mod-11 check digit: 11 minus the weighted sum mod 11, where 11
gives 0 and 10 gives `nil`, a number that is never issued. Used by the
Norwegian fødselsnummer.

# `names`

```elixir
@spec names() :: [atom(), ...]
```

The name of every check `valid?/2` runs.

# `valid?`

```elixir
@spec valid?(atom() | nil, binary()) :: boolean()
```

Runs the named check on a matched value. `nil` accepts every value.

The names are those in `names/0`; any other raises `ArgumentError`.
Separators the pattern allows are dropped by the check itself, so
`"4111 1111 1111 1111"` and `"4111111111111111"` give the same answer.
For a binary value it returns a boolean and does not raise.

---

*Consult [api-reference.md](api-reference.md) for complete listing*