feat: Add individual checker files and add helper functions

src/fieldCheckers/dayOfMonthChecker.ts

@@ -0,0 +1,15 @@
+import { CronData, Options } from '../index'
+import { err, valid } from '../result'
+import checkField from '../helper'
+
+const checkDaysOfMonth = (cronData: CronData, options: Options) => {
+  if (!cronData.daysOfMonth) {
+    return err(['daysOfMonth field is undefined.'])
+  }
+
+  const { daysOfMonth } = cronData
+
+  return checkField(daysOfMonth, 'daysOfMonth', options)
+}
+
+export default checkDaysOfMonth

src/fieldCheckers/dayOfWeekChecker.ts

@@ -0,0 +1,15 @@
+import { CronData, Options } from '../index'
+import { err, valid } from '../result'
+import checkField from '../helper'
+
+const checkDaysOfWeek = (cronData: CronData, options: Options) => {
+  if (!cronData.daysOfWeek) {
+    return err(['daysOfWeek field is undefined.'])
+  }
+
+  const { daysOfWeek } = cronData
+
+  return checkField(daysOfWeek, 'daysOfWeek', options)
+}
+
+export default checkDaysOfWeek

src/fieldCheckers/hourChecker.ts

@@ -0,0 +1,15 @@
+import { CronData, Options } from '../index'
+import { err, valid } from '../result'
+import checkField from '../helper'
+
+const checkHours = (cronData: CronData, options: Options) => {
+  if (!cronData.hours) {
+    return err(['hours field is undefined.'])
+  }
+
+  const { hours } = cronData
+
+  return checkField(hours, 'hours', options)
+}
+
+export default checkHours

src/fieldCheckers/minuteChecker.ts

@@ -0,0 +1,15 @@
+import { CronData, Options } from '../index'
+import { err, valid } from '../result'
+import checkField from '../helper'
+
+const checkMinutes = (cronData: CronData, options: Options) => {
+  if (!cronData.minutes) {
+    return err(['minutes field is undefined.'])
+  }
+
+  const { minutes } = cronData
+
+  return checkField(minutes, 'minutes', options)
+}
+
+export default checkMinutes

src/fieldCheckers/monthChecker.ts

@@ -0,0 +1,15 @@
+import { CronData, Options } from '../index'
+import { err, valid } from '../result'
+import checkField from '../helper'
+
+const checkMonths = (cronData: CronData, options: Options) => {
+  if (!cronData.months) {
+    return err(['months field is undefined.'])
+  }
+
+  const { months } = cronData
+
+  return checkField(months, 'months', options)
+}
+
+export default checkMonths

src/fieldCheckers/secondChecker.ts

@@ -0,0 +1,16 @@
+import { CronData } from '../index'
+import { err, valid } from '../result'
+import checkField from '../helper'
+import { Options } from '../option'
+
+const checkSeconds = (cronData: CronData, options: Options) => {
+  if (!cronData.seconds) {
+    return err(['seconds field is undefined, but useSeconds options is enabled.'])
+  }
+
+  const { seconds } = cronData
+
+  return checkField(seconds, 'seconds', options)
+}
+
+export default checkSeconds

src/fieldCheckers/yearChecker.ts

@@ -0,0 +1,15 @@
+import { CronData, Options } from '../index'
+import { err, valid } from '../result'
+import checkField from '../helper'
+
+const checkYears = (cronData: CronData, options: Options) => {
+  if (!cronData.years) {
+    return err(['years field is undefined, but useYears option is enabled.'])
+  }
+
+  const { years } = cronData
+
+  return checkField(years, 'years', options)
+}
+
+export default checkYears

src/helper.ts

@@ -0,0 +1,169 @@
+import { CronData, CronFieldType } from './index'
+import { Err, err, Valid, valid } from './result'
+import checkSeconds from './fieldCheckers/secondChecker'
+import { Options } from './option'
+
+const checkSingleElement = (
+  element: string,
+  cronFieldType: CronFieldType,
+  options: Options
+) => {
+  if (element === '*') {
+    return valid(true)
+  }
+
+  if (element === '') {
+    return err(`One of the elements is empty in ${cronFieldType} field.`)
+  }
+
+  const number = Number(element)
+  if (isNaN(number)) {
+    return err(`Element '${element} of ${cronFieldType} field is invalid.`)
+  }
+
+  const lowerLimit = options[cronFieldType]?.lowerLimit
+  const upperLimit = options[cronFieldType]?.upperLimit
+  if (number < lowerLimit) {
+  }
+
+  return valid(true)
+}
+
+const checkRangeElement = (
+  element: string,
+  cronFieldType: CronFieldType,
+  options: Options
+) => {
+  if (element === '*') {
+    return err(`'*' can't be part of a range in ${cronFieldType} field.`)
+  }
+
+  if (element === '') {
+    return err(`One of the range elements is empty in ${cronFieldType} field.`)
+  }
+
+  const number = Number(element)
+  if (isNaN(number)) {
+    return err(`Element '${element} of ${cronFieldType} field is invalid.`)
+  }
+
+  return valid(true)
+}
+
+const checkFirstStepElement = (
+  firstStepElement: string,
+  cronFieldType: CronFieldType,
+  options: Options
+) => {
+  const rangeArray = firstStepElement.split('-')
+  if (rangeArray.length > 3) {
+    return err(
+      `List element '${firstStepElement}' is not valid. (More than one '-')`
+    )
+  }
+
+  if (rangeArray.length === 1) {
+    return checkSingleElement(rangeArray[0], cronFieldType, options)
+  } else if (rangeArray.length === 2) {
+    const firstRangeElementResult = checkRangeElement(
+      rangeArray[0],
+      cronFieldType,
+      options
+    )
+    const secondRangeElementResult = checkRangeElement(
+      rangeArray[1],
+      cronFieldType,
+      options
+    )
+
+    if (firstRangeElementResult.isError()) {
+      return firstRangeElementResult
+    }
+
+    if (secondRangeElementResult.isError()) {
+      return secondRangeElementResult
+    }
+
+    if (rangeArray[0] > rangeArray[1]) {
+      return err(
+        `Lower range end '${rangeArray[0]}' is bigger than upper range end '${rangeArray[1]}' of ${cronFieldType} field.`
+      )
+    }
+
+    return valid(true)
+  }
+
+  return err(
+    'Some other error in checkFirstStepElement (rangeArray less than 1)'
+  )
+}
+
+const checkListElement = (
+  listElement: string,
+  cronFieldType: CronFieldType,
+  options: Options
+) => {
+  const stepArray = listElement.split('/')
+  if (stepArray.length > 3) {
+    return err(
+      `List element '${listElement}' is not valid. (More than one '/')`
+    )
+  }
+
+  const firstElementResult = checkFirstStepElement(
+    stepArray[0],
+    cronFieldType,
+    options
+  )
+
+  if (firstElementResult.isError()) {
+    return firstElementResult
+  }
+
+  if (stepArray.length === 2) {
+    // check second element (x) of */x
+  }
+
+  return valid(true)
+}
+
+const checkField = (
+  cronField: string,
+  cronFieldType: CronFieldType,
+  options: Options
+) => {
+  if (
+    ![
+      'seconds',
+      'minutes',
+      'hours',
+      'daysOfMonth',
+      'months',
+      'daysOfWeek',
+      'years',
+    ].includes(cronFieldType)
+  ) {
+    return err([`Cron field type '${cronFieldType}' does not exist.`])
+  }
+
+  // Check for lists e.g. 4,5,6,8-18,20-40/2
+  const listArray = cronField.split(',')
+  const checkResults: (Valid<boolean, unknown> | Err<unknown, string>)[] = []
+  listArray.forEach((listElement: string) => {
+    checkResults.push(checkListElement(listElement, cronFieldType, options))
+  })
+
+  if (checkResults.every(value => value.isValid())) {
+    return valid(true)
+  }
+
+  const errorArray: string[] = []
+  checkResults.forEach(result => {
+    if (result.isError()) {
+      errorArray.push(result.getError())
+    }
+  })
+  return err(errorArray)
+}
+
+export default checkField