# @nithin-sivakumar/genotp

A lightweight and secure OTP (One-Time Password) generator for JavaScript with customizable features like length, character set, prefix, suffix, and base64 encoding.

## Features

- **Secure OTP Generation**: Uses `crypto` module for secure, random OTP generation.
- **Customizable Length**: Generate OTPs of any length.
- **Multiple Character Sets**:
  - Numeric: `0123456789`
  - Alphanumeric: `ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789`
  - Custom: Use a custom character set of your choice.
- **Prefix and Suffix**: Optionally add a prefix or suffix to your OTP.
- **Base64 Encoding**: Optionally return the OTP as a base64-encoded string.
- **No Expiry Handling**: This package only focuses on OTP generation; expiry is left to the user.

## Installation

To install the package, run:

```bash
npm install @nithin-sivakumar/genotp
```

## Usage

### Generate OTP

To generate an OTP, use the `generate` function with the following options:

```javascript
import { generate } from "@nithin-sivakumar/genotp";

// Generate Numeric OTP of length 6
const otp = generate(6, "numeric");
console.log("Generated Numeric OTP:", otp);

// Generate Alphanumeric OTP with a prefix
const otpWithPrefix = generate(8, "alphanumeric", "", "OTP-", "");
console.log("Generated OTP with Prefix:", otpWithPrefix);

// Generate OTP with a custom character set
const customCharSet =
  "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789!@#";
const otpWithCustomCharSet = generate(10, "custom", customCharSet);
console.log("Generated OTP with Custom Character Set:", otpWithCustomCharSet);

// Generate Base64-encoded OTP
const base64Otp = generate(10, "alphanumeric", "", "", "", true);
console.log("Base64 Encoded OTP:", base64Otp);
```

### Options for `generate` function:

- **`length`** (number): The length of the OTP. Default is `6`.
- **`mode`** (string): The mode of OTP generation:
  - `'numeric'`: OTP contains only numbers.
  - `'alphanumeric'`: OTP contains numbers and letters (both uppercase).
  - `'custom'`: OTP uses a custom character set. Default is `'numeric'`.
- **`charSet`** (string): Custom characters to use for OTP generation (only for `custom` mode). Default is empty.
- **`prefix`** (string): Optional prefix to be added to the OTP. Default is `""`.
- **`suffix`** (string): Optional suffix to be added to the OTP. Default is `""`.
- **`base64Encode`** (boolean): Whether to return the OTP as a base64-encoded string. Default is `false`.

## Example

```javascript
import { generate } from "@nithin-sivakumar/genotp";

// Generate OTP of length 6 using numeric characters
const otp = generate(6, "numeric");
console.log(otp); // Example: 123456

// Generate OTP of length 8 using alphanumeric characters
const otpAlphanumeric = generate(8, "alphanumeric");
console.log(otpAlphanumeric); // Example: A1B2C3D4

// Generate OTP with custom character set
const customOtp = generate(
  10,
  "custom",
  "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789!@#"
);
console.log(customOtp); // Example: aB1!jK8@
```

## Error Handling

The package throws the following errors:

- **Invalid Mode or Character Set**: If the mode or character set is invalid, an error will be thrown.
- **Invalid Length**: If the length is less than or equal to 0, an error will be thrown.

## License

MIT License. See [LICENSE](LICENSE) for more information.