feat: add static method getDaysOfMonth on NepaliDate (#96)

Author: aj3sh

README.md

@@ -215,6 +215,10 @@ const date2 = NepaliDate.fromEnglishDate(2023, 6, 8, 10, 15)
 console.log(date2.toString()) // 2080-03-23 10:15:00
 ```
 
+#### Others
+
+-   `NepaliDate.getDaysOfMonth(year, month)`: Returns the number of days in a specific month of a given year.
+
 ### dateConverter
 
 The `dateConverter` module provides core functions for converting dates between the Nepali and English calendars.

src/NepaliDate.ts

@@ -1,4 +1,5 @@
 import dateConverter from './dateConverter'
+import { NP_MONTHS_DATA } from './dateConverter/constants'
 import {
     format,
     formatEnglishDate,
@@ -642,6 +643,26 @@ class NepaliDate {
         )
         return NepaliDate.fromEnglishDate(year, month0, day, hour, minute, second, ms)
     }
+
+    /**
+     * Returns the number of days in a specific month of a given year.
+     *
+     * @param year - The year to fetch the month from.
+     * @param month - The month to get the number of days for.
+     * @returns The number of days in the specified month.
+     * @throws {Error} If the year or month is out of range.
+     */
+    static getDaysOfMonth(year: number, month: number): number {
+        if (year < dateConverter.npMinYear() || year > dateConverter.npMaxYear()) {
+            throw new Error('Year out of range')
+        }
+
+        if (month < 0 || month > 11) {
+            throw new Error('Month out of range')
+        }
+
+        return NP_MONTHS_DATA[year - dateConverter.npMinYear()][0][month]
+    }
 }
 
 NepaliDate.minimum = () =>

tests/NepaliDate.test.ts

@@ -1,3 +1,4 @@
+import dateConverter from '../src/dateConverter'
 import NepaliDate from '../src/NepaliDate'
 import { ValidationError } from '../src/validators'
 
@@ -741,3 +742,48 @@ describe('NepaliDate with Time feature: set methods', () => {
         })
     })
 })
+
+describe('NepaliDate.getDaysOfMonth', () => {
+    it('should return the correct number of days for a valid year and month', () => {
+        const days = NepaliDate.getDaysOfMonth(2081, 8)
+        expect(days).toBe(29)
+    })
+
+    it('should return the correct number of days for a year 2000 and month 0', () => {
+        const days = NepaliDate.getDaysOfMonth(2000, 0)
+        expect(days).toBe(30)
+    })
+
+    it('should return the correct number of days for a year 2099 and month 11', () => {
+        const days = NepaliDate.getDaysOfMonth(2099, 11)
+        expect(days).toBe(30)
+    })
+
+    it('should throw an error if the year is below the valid range', () => {
+        const invalidYear = dateConverter.npMinYear() - 1
+        expect(() => NepaliDate.getDaysOfMonth(invalidYear, 0)).toThrow(
+            'Year out of range'
+        )
+    })
+
+    it('should throw an error if the year is above the valid range', () => {
+        const invalidYear = dateConverter.npMaxYear() + 1
+        expect(() => NepaliDate.getDaysOfMonth(invalidYear, 0)).toThrow(
+            'Year out of range'
+        )
+    })
+
+    it('should throw an error if the month is below 0', () => {
+        const validYear = dateConverter.npMinYear()
+        expect(() => NepaliDate.getDaysOfMonth(validYear, -1)).toThrow(
+            'Month out of range'
+        )
+    })
+
+    it('should throw an error if the month is greater than 11', () => {
+        const validYear = dateConverter.npMinYear()
+        expect(() => NepaliDate.getDaysOfMonth(validYear, 12)).toThrow(
+            'Month out of range'
+        )
+    })
+})