# mask-pii (Elixir)

Version: 0.2.0

A lightweight, customizable Elixir library for masking Personally Identifiable Information (PII) such as **email addresses** and **phone numbers**.

It is designed to be safe, fast, and easy to integrate into logging or data processing pipelines.

Official website: https://finitefield.org/en/oss/mask-pii
Developed by: [Finite Field, K.K.](https://finitefield.org/en/)

## Features

- **Email Masking:** Masks the local part while preserving the domain (e.g., `a****@example.com`).
- **Global Phone Masking:** Detects international phone formats and masks all digits except the last 4.
- **Customizable:** Change the masking character (default is `*`).
- **Zero Unnecessary Dependencies:** Pure Elixir implementation.

## Installation

Add `:mask_pii` to your dependencies:

```elixir
# mix.exs
{:mask_pii, "~> 0.2.0"}
```

Then fetch dependencies:

```bash
mix deps.get
```

From a local checkout:

```bash
mix deps.get
mix deps.compile
```

## Usage

```elixir
alias MaskPII.Masker

masker =
  Masker.new()
  |> Masker.mask_emails()
  |> Masker.mask_phones()
  |> Masker.with_mask_char("#")

input_text = "Contact: alice@example.com or 090-1234-5678."
output = Masker.process(masker, input_text)

IO.puts(output)
# => "Contact: a####@example.com or ###-####-5678."
```

## Configuration

The `Masker` module uses a builder-style API. By default, `Masker.new()` performs **no masking** (pass-through).

### Builder Functions

| Function | Description | Default |
| --- | --- | --- |
| `mask_emails/1` | Enables detection and masking of email addresses. | Disabled |
| `mask_phones/1` | Enables detection and masking of global phone numbers. | Disabled |
| `with_mask_char/2` | Sets the character used for masking (e.g., `"*"`, `"#"`, `"x"`). | `"*"` |

### Masking Logic Details

**Emails**
- **Pattern:** Detects standard email formats.
- **Behavior:** Keeps the first character of the local part and the domain. Masks the rest of the local part.
- **Example:** `alice@example.com` -> `a****@example.com`
- **Short Emails:** If the local part is 1 character, it is fully masked (e.g., `a@b.com` -> `*@b.com`).

**Phones (Global Support)**
- **Pattern:** Detects sequences of digits that look like phone numbers (supports international `+81...`, US `(555)...`, and hyphenated `090-...`).
- **Behavior:** Preserves formatting (hyphens, spaces, parentheses) and the **last 4 digits**. All other digits are replaced.
- **Examples:**
  - `090-1234-5678` -> `***-****-5678`
  - `+1 (800) 123-4567` -> `+* (***) ***-4567`
  - `12345` -> `*2345`