npm package: @schul-cloud/commons
Description: Helpers and common tools for the hpi school-cloud.
Latest version: 1.3.0

# Commons

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## Install

    npm install @schul-cloud/commons --save

## Test

    npm install
    npm test

## Usage

### Configuration

The `Configuration` is a singleton that can be reused to hold a configuration that is validated by JSON Schema. A JSON-Schema has to be defined as `default.schema.json` inside a `config` folder.

The configuration is build by parsing multiple sources in the following order (Last definition overrides definition from before):

1. defaults from `default.schema.json`
2. defaults from `default.json` (values have to be defined here, for properties required in the schema too beside the schema default)
3. parse configuration files from environment
   1. `NODE_ENV.json` from config folder (defaults to `development.json`, if `NODE_ENV` is not defined - the file existence is optionally)
   2. Other environment files can be added into options.loadFilesFromEnv after `NODE_ENV` by default, `SC_INSTANCE`.
4. `.env` file from execution/project root directory
5. existing environment variables finally override everything from before.

The default schema parser options

1. remove all options from upper sources if the schema contains the property `"additionalProperties": false`
2. applying default values
3. do a [type conversion](https://ajv.js.org/coercion.html) especially for string to type conversion values not defined in the json files (string to X).

Invalid input values will raise an error by default.

To enable multiple inherited objects when parsing environment variables there may be a dot notation be used. When enabled, this gets applied for export, has, and get too. Currently only `__` (double underscore) is supported as separator due to the dependency [dotenv](https://www.npmjs.com/package/dotenv#should-i-have-multiple-env-files) and bad support of `.` (single dot) in many terminals.

#### Secrets

There exist a method `printHierarchy()` to print the whole hierarchy of a configuration. For security reasons, by default all values of string typed properties having secret or key in their name will be replaced with a hash-id. Same hashes identify same original values.

> Use the naming convention to start secure properties with `SECRET_` in their name and use type string.

#### Specifying Dependencies

Often specific configuration options are required based on the state of other configuration values.
These dependencies can be defined using the [if/then/else keywords](https://github.com/epoberezkin/ajv/blob/master/KEYWORDS.md#ifthenelse).

In the example below the rule `SERVICE_REQUIRES_OTHER` rule is activated in the `allOf` block.
The rule itself is defined in the `definitions` block.
If the property `SERVICE_PROPERTY` is set to `VALUE_OF_SERVICE` we also require that `OTHER_PROPERTY` is set.
Make sure that a default value is set for `SERVICE_PROPERTY` [to avoid passing undefined to an if keyword](https://github.com/epoberezkin/ajv/issues/913).

### Sample

default.schema.json

    {
        "title": "Example Schema with dependency",
        "description": "This schema declares a dependency between two properties.",
        "additionalProperties": false,
        "type": "object",
        "properties": {
            "SERVICE_PROPERTY": {
                "type": "string",
                "enum": ["none", "VALUE_OF_SERVICE"],
                "default": "none"
            },
            "OTHER_PROPERTY": {
                "type": "string"
            }
        },
        "allOf": [
            {
                "$ref": "#/definitions/SERVICE_REQUIRES_OTHER"
            }
        ],
        "definitions": {
            "SERVICE_REQUIRES_OTHER": {
                "if": {
                    "properties": {
                        "SERVICE_PROPERTY": {
                            "const": "VALUE_OF_SERVICE"
                        }
                    }
                },
                "then": {
                    "required": ["OTHER_PROPERTY"]
                }
            }
        }
    }

default.json

    {
        "$schema": "default.schema.json",
        "SERVICE_PROPERTY": "VALUE_OF_SERVICE",
        "OTHER_PROPERTY": "VALUE"
    }

index.js

    // Access Configuration as Singleton, using default export
    // Initialization is done on first access
    // uses IConfigOptions optionally defined in a sc-config.json file
    import { Configuration as config } from "@schul-cloud/commons";

    // Access configuration as class
    // IConfigOptions can be set in constructor options
    import { TestConfiguration } from "@schul-cloud/commons";
    const config = new TestConfiguration(options);

    // Then you may run...
    config.has("key");
    const before = config.toObject();
    // and when the property key has been defined in the schema...
    config.get("key");
    config.set("key", "value");
    // or updating multiple entries
    config.update({...});

    // suggested for testing only
    config.remove("key"); // removes a single key
    config.remove("key", "key2", ...); // remove multiple keys
    // override the complete config (removes prior values)
    config.reset(before);

### Options

| Option&nbsp;key  | Value(s)&nbsp;or&nbsp;Type | default                                                           | Description                                                                                                                                                                                   |
| ---------------- | -------------------------- | ----------------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| logger           | `any`                      | `console`                                                         | a logger instance                                                                                                                                                                             |
| throwOnError     | `boolean`                  | `true`                                                            | enable throwing an error when an undefined configuration value is requested                                                                                                                   |
| notFoundValue    | `any`                      | `null`                                                            | if throwOnError is not set true, an alternate default value may returned                                                                                                                      |
| configDir        | `string`                   | `config`                                                          | directory where schema and configuration files are located                                                                                                                                    |
| schemaFileName   | `string`                   | `default.schema.json`                                             | default schema file name                                                                                                                                                                      |
| baseDir          | `string`                   | `process.cwd`()                                                   | path to folder where configDir is located                                                                                                                                                     |
| ajvOptions       | `object`                   | `removeAdditional: 'true' useDefaults: true coerceTypes: 'array'` | Schema Parser Options, see <https://github.com/epoberezkin/ajv#options>                                                                                                                       |
| useDotNotation   | `boolean`                  | `true`                                                            | enables dot notation for parsing environment variables (not json files!) and exporting the current config using has, get, and toObject.                                                       |
| fileEncoding     | `string`                   | `'utf8'`                                                          | set file encoding for imported schema and configuration files                                                                                                                                 |
| loadFilesFromEnv | `string[]`                 | `['NODE_ENV']`                                                    | defines the order of configuration files loaded by specified environment values filename must have json extension like NODE_ENV.json                                                          |
| printHierarchy   | `boolean`                  | `false`                                                           | executes printHierarchy() right after initialization                                                                                                                                          |
| printSecrets     | `boolean`                  | `false`                                                           | by default, secrets are replaced by hashes which are equal for same values using printHierarchy function. Set this `true` to print configuration values of keys containing `secret` or `key`. |
| secretMatches    | `string[]`                 | `['SECRET', 'KEY', 'SALT', 'PASSWORD']`                           | properties matching these expressions (flags added are `/gi`) are handled as secrets and will be hashed before printing                                                                       |

## JSON Schema

### Enhanced validation

Custom validation keywords may be added to get detailed error messages for specific checks:
<https://medium.com/@moshfeu/test-json-schema-with-ajv-and-jest-c1d2984234c9>

### Dependencies

Multiple supported [keywords](https://github.com/epoberezkin/ajv/blob/master/KEYWORDS.md#keywords) exist in ajv to define dependencies.

## Use cases

- To apply NODE_ENV-specific defaults, use NODE_ENV.json-file in config folder
- To apply global defaults, set default in schema file itself
- To apply secrets, set values using .env file (never commit this file!)
- To apply feature-flag conditions, see dependency [keywords](https://github.com/epoberezkin/ajv/blob/master/KEYWORDS.md#keywords) above.