# SAP BTP Feature Toggle Library

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SAP BTP feature toggle library enables Node.js applications using the SAP Cloud Application Programming Model to maintain live-updatable feature toggles via Redis.

## Getting Started (CAP Feature Toggles)

- Set up project with `@sap/cds`.
- Install library:

  ```bash
  npm install --save @cap-js-community/feature-toggle-library
  ```

- For CAP Feature Toggles everything is configured automatically.
- The library acts as a CDS-Plugin and registers a `FeatureService`, which can be used to check and update toggles.
- For details see [Example CAP Server](https://github.com/cap-js-community/feature-toggle-library/blob/main/example-cap-server).

## Getting Started (Custom Configuration)

- Same as previous section.
- Write `toggles.yaml` configuration file:

  ```yaml
  # info: check api priority; 0 means access is disabled
  /check/priority:
    type: number
    fallbackValue: 0
    validations:
      - scopes: [user, tenant]
      - regex: '^\d+$'
  ```

- Add configuration path to `package.json`:

  ```json
  {
    "cds": {
      "featureToggles": {
        "configFile": "./toggles.yaml"
      }
    }
  }
  ```

- Write usage code in handlers:

  ```javascript
  const toggles = require("@cap-js-community/feature-toggle-library");

  const priorityHandler = async (context) => {
    const user = context.user.id;
    const tenant = context.tenant;
    const value = toggles.getFeatureValue("/check/priority", { user, tenant });
    if (value <= 0) {
      return context.reject("blocked");
    } else if (value < 10) {
      return context.reply("welcome");
    } else {
      return context.reply("very welcome");
    }
  };
  ```

## Features

- Maintain feature toggle states consistently across multiple app instances.
- Feature toggle changes are published from Redis to subscribed app instances with publish/subscribe pattern [PUB/SUB](https://redis.io/topics/pubsub).
- Horizontal app scaling is supported and new app instances will start with the correct state, or fallback values, if they cannot connect to Redis.
- Feature toggle values can be changed specifically for accessors with certain scopes, e.g., for specific tenants, users,...
- Users can register change handler callbacks for specific toggles.
- Users can register custom input validation callbacks for specific toggles.
- Works as a [CDS-Plugin](https://cap.cloud.sap/docs/node.js/cds-plugins) and provides a REST service to read and manipulate toggles.

## Peers

- [CAP Extensibility Feature Toggles](https://cap-js-community.github.io/feature-toggle-library/peers/#cap-extensibility-feature-toggles)
- [SAP Feature Flags Service](https://cap-js-community.github.io/feature-toggle-library/peers/#sap-feature-flags-service)

## Documentation

Head over to our [Documentation](https://cap-js-community.github.io/feature-toggle-library/) to learn more.

## Support, Feedback, Contributing

This project is open to feature requests/suggestions, bug reports etc. via [GitHub issues](https://github.com/cap-js-community/feature-toggle-library/issues). Contribution and feedback are encouraged and always welcome. For more information about how to contribute, the project structure, as well as additional contribution information, see our [Contribution Guidelines](CONTRIBUTING.md).

## Code of Conduct

We as members, contributors, and leaders pledge to make participation in our community a harassment-free experience for everyone. By participating in this project, you agree to abide by its [Code of Conduct](CODE_OF_CONDUCT.md) at all times.

## Licensing

Copyright 2023 SAP SE or an SAP affiliate company and feature-toggle-library contributors. Please see our [LICENSE](LICENSE) for copyright and license information. Detailed information including third-party components and their licensing/copyright information is available [via the REUSE tool](https://api.reuse.software/info/github.com/cap-js-community/feature-toggle-library).