npm package: @lobaro/lobaro-cron-validate
Description: lobaro modifyed cron-validate is a cron-expression validator written in TypeScript.
Author: Lobaro additions on the original Airfox lib from: Konstantin L. 'Airfox' Zisiadis
Latest version: 1.0.0

# cron-validate

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Cron-validate is a cron-expression validator written in TypeScript. This is a fork with adaptions to validate Lobaro Device Crons
The validation options are customizable and cron fields like seconds and years are supported. The fork aims to support all options from the original repo and 
to amend whats needed for the Lobaro Crons 

## Lobaro Modifications
- Support Lobaro CRON validations for `H,L,W`
- Adding `/lib` to repo and skip release, requires `npm run build` to update compiled files in `/lib`


## Usage

### Basic usage

```typescript
import cron from 'cron-validate'

const cronResult = cron('* * * * *')
if (cronResult.isValid()) {
  // !cronResult.isError()
  // valid code
} else {
  // error code
}
```

### Result system

The `cron` function returns a Result-type, which is either `Valid<T, E>` or `Err<T, E>`.

For checking the returned result, just use `result.isValid()` or `result.isError()`

Both result types contain values:

```typescript
import cron from 'cron-validate'

const cronResult = cron('* * * * *')
if (cronResult.isValid()) {
  const validValue = cronResult.getValue()

  // The valid value is a object containing all cron fields
  console.log(validValue)
  // In this case, it would be:
  // { seconds: undefined, minutes: '*', hours: '*', daysOfMonth: '*', months: '*', daysOfWeek: '*', years: undefiend }
} else {
  const errorValue = cronResult.getError()

  // The error value contains an array of strings, which represent the cron validation errors.
  console.log(errorValue) // string[] of error messages
}
```

Make sure to test the result type beforehand, because `getValue()` only works on `Valid` and `getError()` only works on `Err`. If you don't check, it will throw an error.

For further information, you can check out https://github.com/gDelgado14/neverthrow, because I used and modified his code for this package.
(Therefor not every documented function on his package is available on this package.)

## Options / Configuration

To configure the validator, cron-validate uses a preset system. There are already defined presets (default, npm-node-cron or aws), but you can also define your own preset to use for your system. You can also use the override property to set certain option on single cron validates.

### Presets

The following presets are already defined by cron-validate:

- default (see: http://crontab.org/)
- npm-node-cron (see: https://github.com/kelektiv/node-cron)
- aws-cloud-watch (see: https://docs.aws.amazon.com/de_de/AmazonCloudWatch/latest/events/ScheduledEvents.html)
- npm-cron-schedule (see: https://github.com/P4sca1/cron-schedule)

To select a preset for your validation, you can simply do this:

```typescript
cron('* * * * *', {
  preset: 'npm-cron-schedule',
})
```

#### Defining and using your own preset

To define your own preset, use this:

```typescript
registerOptionPreset('YOUR-PRESET-ID', {
  presetId: 'YOUR-PRESET-ID',
  useSeconds: false,
  useYears: false,
  useAliases: false, // optional, default to false
  useBlankDay: false,
  allowOnlyOneBlankDayField: false,
  mustHaveBlankDayField: false, // optional, default to false
  useLastDayOfMonth: false, // optional, default to false
  useLastDayOfWeek: false, // optional, default to false
  useNearestWeekday: false, // optional, default to false
  useNthWeekdayOfMonth: false, // optional, default to false
  seconds: {
    minValue: 0,
    maxValue: 59,
    lowerLimit: 0, // optional, default to minValue
    upperLimit: 59, // optional, default to maxValue
  },
  minutes: {
    minValue: 0,
    maxValue: 59,
    lowerLimit: 0, // optional, default to minValue
    upperLimit: 59, // optional, default to maxValue
  },
  hours: {
    minValue: 0,
    maxValue: 23,
    lowerLimit: 0, // optional, default to minValue
    upperLimit: 23, // optional, default to maxValue
  },
  daysOfMonth: {
    minValue: 1,
    maxValue: 31,
    lowerLimit: 1, // optional, default to minValue
    upperLimit: 31, // optional, default to maxValue
  },
  months: {
    minValue: 0,
    maxValue: 12,
    lowerLimit: 0, // optional, default to minValue
    upperLimit: 12, // optional, default to maxValue
  },
  daysOfWeek: {
    minValue: 1,
    maxValue: 7,
    lowerLimit: 1, // optional, default to minValue
    upperLimit: 7, // optional, default to maxValue
  },
  years: {
    minValue: 1970,
    maxValue: 2099,
    lowerLimit: 1970, // optional, default to minValue
    upperLimit: 2099, // optional, default to maxValue
  },
})
```

The preset properties explained:

- `presetId: string`
  - same id as in first function parameter
- `useSeconds: boolean`
  - enables seconds field in cron expression
- `useYears: boolean`
  - enables years field in cron expression
- `useAliases: boolean`
  - enables aliases for month and daysOfWeek fields (ignores limits for month and daysOfWeek, so be aware of that)
- `useBlankDay: boolean`
  - enables blank day notation '?' in daysOfMonth and daysOfWeek field
- `allowOnlyOneBlankDayField: boolean`
  - requires a day field to not be blank (so not both day fields can be blank)
- `mustHaveBlankDayField: boolean`
  - requires a day field to be blank (so not both day fields are specified)
  - when mixed with `allowOnlyOneBlankDayField`, it means that there will always be either day or day of week as `?`
- `useLastDayOfMonth: boolean`
  - enables the 'L' character to specify the last day of the month.
  - accept negative offset after the 'L' for nth last day of the month.
  - e.g.: `L-2` would me the 2nd to last day of the month.
- `useLastDayOfWeek: boolean`
  - enables the 'L' character to specify the last occurrence of a weekday in a month.
  - e.g.: `5L` would mean the last friday of the month.
- `useNearestWeekday: boolean`
  - enables the 'W' character to specify the use of the closest weekday.
  - e.g.: `15W` would mean the weekday (mon-fri) closest to the 15th when the 15th is on sat-sun.
- `useNthWeekdayOfMonth: boolean`
  - enables the '#' character to specify the Nth weekday of the month.
  - e.g.: `6#3` would mean the 3rd friday of the month (assuming 6 = friday).

* in cron fields (like seconds, minutes etc.):
  - `minValue: number`
    - minimum value of your cron interpreter (like npm-node-cron only supports 0-6 for weekdays)
    - can't be set as override
  - `maxValue: number`
    - minimum value of your cron interpreter (like npm-node-cron only supports 0-6 for weekdays)
    - can't be set as override
  - `lowerLimit?: number`
    - lower limit for validation
    - equal or greater than minValue
    - if not set, default to minValue
  - `upperLimit?: number`
    - upper limit for validation
    - equal or lower than maxValue
    - if not set, defaults to maxValue

### Override preset options

If you want to override a option for single cron validations, you can use the `override` property:

```typescript
console.log(cron('* * * * * *', {
  preset: 'default' // second field not supported in default preset
  override: {
    useSeconds: true // override preset option
  }
}))

console.log(cron('* 10-20 * * * *', {
  preset: 'default'
  override: {
    minutes: {
      lowerLimit: 10, // override preset option
      upperLimit: 20 // override preset option
    }
  }
}))
```

## Examples

```typescript
import cron from 'cron-validate'

console.log(cron('* * * * *').isValid()) // true

console.log(cron('* * * * *').isError()) // false

console.log(cron('* 2,3,4 * * *').isValid()) // true

console.log(cron('0 */2 */5 * *').isValid()) // true

console.log(cron('* * * * * *', { override: { useSeconds: true } }).isValid()) // true

console.log(cron('* * * * * *', { override: { useYears: true } }).isValid()) // true

console.log(
  cron('30 * * * * *', {
    override: {
      useSeconds: true,
      seconds: {
        lowerLimit: 20,
        upperLimit: 40,
      },
    },
  }).isValid()
) // true

console.log(
  cron('* 3 * * *', {
    override: {
      hours: {
        lowerLimit: 0,
        upperLimit: 2,
      },
    },
  }).isValid()
) // false

console.log(
  cron('* * ? * *', {
    override: {
      useBlankDay: true,
    },
  }).isValid()
) // true

console.log(
  cron('* * ? * ?', {
    override: {
      useBlankDay: true,
      allowOnlyOneBlankDayField: true,
    },
  }).isValid()
) // false
```

## (Planned) Features

- [x] Basic cron validation.
- [x] Error messenges with information about invalid cron expression.
- [x] Seconds field support.
- [x] Years field support.
- [x] Option presets (classic cron, node-cron, etc.)
- [x] Blank '?' daysOfMonth/daysOfWeek support
- [x] Last day of month.
- [x] Last specific weekday of month. (e.g. last Tuesday)
- [x] Closest weekday to a specific day of the month.
- [x] Nth specific weekday of month. (e.g. 2nd Tuesday)
- [x] Cron alias support.

<hr />

### Contributors

 <ul>
    <li>
        <a href="https://github.com/Airfooox">Airfooox</a>
    </li>
    <li>
        <a href="https://github.com/GuillaumeRochat">GuillaumeRochat</a>
    </li>
 </ul>

<hr />

### Used by:
 <ul>
    <li>
        <a href="https://github.com/breejs/bree">Bree - Job Scheduler For NodeJS</a>
    </li>
 </ul>

<hr />