feat: 숫자를 날짜를 나타내는 순우리말로 바꿔주는 함수 중 days를 추가

.changeset/spicy-teachers-admire.md

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+---
+"es-hangul": minor
+---
+
+feat: 숫자를 날짜를 나타내는 순우리말로 바꿔주는 함수 중 days를 추가

docs/src/pages/docs/api/date.en.mdx

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+---
+title: date
+---
+
+import { Sandpack } from '@/components/Sandpack';
+
+# date
+
+Convert numbers to native Korean words representing dates. The given number is valid when it is greater than 0 and less than or equal to 30.
+
+## days
+
+Convert numbers to native Korean words for days.
+
+```typescript
+function days(
+  // Number to convert
+  num: number
+): string;
+```
+
+### Examples
+
+```typescript
+days(1); // '하루'
+days(2); // '이틀'
+days(3); // '사흘'
+days(10); // '열흘'
+days(11); // '열하루'
+days(20); // '스무날'
+days(29); // '스무아흐레'
+days(30); // '서른날'
+```
+
+### Demo
+
+<br />
+
+<Sandpack>
+
+```ts index.ts
+import { days } from 'es-hangul';
+
+console.log(days(3));
+console.log(days(4));
+```
+
+</Sandpack>

docs/src/pages/docs/api/date.ko.mdx

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+---
+title: date
+---
+
+import { Sandpack } from '@/components/Sandpack';
+
+# date
+
+숫자를 날짜를 나타내는 순우리말로 바꿔줍니다. 주어진 숫자가 0보다 크고 30 이하일 때 유효합니다.
+
+## days
+
+숫자를 순우리말 날로 바꿔줍니다.
+
+```typescript
+function days(
+  // 변환할 숫자
+  num: number
+): string;
+```
+
+### Examples
+
+```typescript
+days(1); // '하루'
+days(2); // '이틀'
+days(3); // '사흘'
+days(10); // '열흘'
+days(11); // '열하루'
+days(20); // '스무날'
+days(29); // '스무아흐레'
+days(30); // '서른날'
+```
+
+### 사용해보기
+
+<br />
+
+<Sandpack>
+
+```ts index.ts
+import { days } from 'es-hangul';
+
+console.log(days(3));
+console.log(days(4));
+```
+
+</Sandpack>

src/date/date.spec.ts

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+import { days } from '.';
+
+describe('date', () => {
+  describe('days', () => {
+    const validNumbers = [
+      { num: 1, word: '하루' },
+      { num: 2, word: '이틀' },
+      { num: 3, word: '사흘' },
+      { num: 4, word: '나흘' },
+      { num: 5, word: '닷새' },
+      { num: 6, word: '엿새' },
+      { num: 7, word: '이레' },
+      { num: 8, word: '여드레' },
+      { num: 9, word: '아흐레' },
+      { num: 10, word: '열흘' },
+      { num: 11, word: '열하루' },
+      { num: 20, word: '스무날' },
+      { num: 21, word: '스무하루' },
+      { num: 30, word: '서른날' },
+    ];
+
+    const invalidNumbers = [0, -1, 31, 1.1, -1.1, Infinity, -Infinity, NaN];
+
+    validNumbers.forEach(({ num, word }) => {
+      it(`${num} - 순 우리말 날짜 ${word}로 바꿔 반환해야 한다.`, () => {
+        expect(days(num)).toBe(word);
+      });
+    });
+
+    invalidNumbers.forEach(num => {
+      it(`유효하지 않은 숫자 ${num}에 대해 오류를 발생시켜야 한다.`, () => {
+        expect(() => days(num)).toThrow('지원하지 않는 숫자입니다.');
+      });
+    });
+  });
+});

src/date/days.constants.ts

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+export const DAYS_MAP = {
+  1: '하루',
+  2: '이틀',
+  3: '사흘',
+  4: '나흘',
+  5: '닷새',
+  6: '엿새',
+  7: '이레',
+  8: '여드레',
+  9: '아흐레',
+  10: '열',
+  20: '스무',
+} as const;
+
+export const DAYS_ONLY_TENS_MAP = {
+  10: '열흘',
+  20: '스무날',
+  30: '서른날',
+} as const;

src/date/index.ts

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+import { hasProperty } from '../_internal';
+import { DAYS_MAP, DAYS_ONLY_TENS_MAP } from './days.constants';
+
+export function days(num: number): string {
+  return getNumberWord(num);
+}
+
+function getNumberWord(num: number): string {
+  validateNumber(num);
+
+  const tens = Math.floor(num / 10) * 10;
+  const ones = num % 10;
+
+  if (ones === 0 && hasProperty(DAYS_ONLY_TENS_MAP, tens)) {
+    return DAYS_ONLY_TENS_MAP[tens];
+  }
+
+  const tensWord = hasProperty(DAYS_MAP, tens) ? DAYS_MAP[tens] : '';
+  const onesWord = hasProperty(DAYS_MAP, ones) ? DAYS_MAP[ones] : '';
+
+  return `${tensWord}${onesWord}`;
+}
+
+function validateNumber(num: number): void {
+  if (Number.isNaN(num) || num <= 0 || num > 30 || !Number.isInteger(num) || !Number.isFinite(num)) {
+    throw new Error('지원하지 않는 숫자입니다.');
+  }
+}

src/index.ts

@@ -1,6 +1,7 @@
 export { assemble } from './assemble';
 export { combineCharacter, combineVowels } from './combineCharacter';
 export { convertQwertyToHangul, convertQwertyToAlphabet } from './convertQwertyToAlphabet';
+export { days } from './date';
 export { disassemble, disassembleToGroups } from './disassemble';
 export { disassembleCompleteCharacter } from './disassembleCompleteCharacter';
 export { josa } from './josa';