Feat: add reading time and word count display

- Added readingTime utility to calculate word count and reading duration
- Display word count and estimated reading time on article pages
- Added unit tests for reading time calculation
- Based on ~200 characters/words per minute reading speed

Author: JingkaiTang

src/pages/writing/[slug].astro

@@ -2,6 +2,7 @@
 import BaseLayout from '../../layouts/BaseLayout.astro';
 import { getCollection, render } from 'astro:content';
 import { formatShanghai } from '../../utils/dateFormat';
+import { calculateReadingTime } from '../../utils/readingTime';
 
 export async function getStaticPaths() {
   // Include drafts so they can be previewed via direct link.
@@ -18,6 +19,10 @@ const { Content, headings } = await render(post);
 
 const toc = (headings ?? []).filter((h) => h.depth >= 2 && h.depth <= 3);
 const isDraft = Boolean(post.data.draft);
+
+// Calculate reading time from post body content
+const postBody = post.body || '';
+const { words, minutes } = calculateReadingTime(postBody);
 ---
 
 <BaseLayout
@@ -61,6 +66,7 @@ const isDraft = Boolean(post.data.draft);
               </>
             ))}</>
           ) : null}
+          <> · {words} 字 · 约 {minutes} 分钟阅读</>
         </p>
 
         <div class="post-content">

src/utils/readingTime.test.ts

@@ -0,0 +1,40 @@
+import { describe, it, expect } from 'vitest';
+import { calculateReadingTime } from './readingTime';
+
+describe('calculateReadingTime', () => {
+  it('should count Chinese characters correctly', () => {
+    const result = calculateReadingTime('你好世界');
+    expect(result.words).toBe(4);
+    expect(result.minutes).toBe(1);
+  });
+
+  it('should count English words correctly', () => {
+    const result = calculateReadingTime('Hello world test');
+    expect(result.words).toBe(3);
+    expect(result.minutes).toBe(1);
+  });
+
+  it('should handle mixed content', () => {
+    const result = calculateReadingTime('你好 Hello 世界 world');
+    expect(result.words).toBe(6);
+  });
+
+  it('should calculate reading time for longer content', () => {
+    // 400 Chinese characters should be ~2 minutes
+    const longText = '你'.repeat(400);
+    const result = calculateReadingTime(longText);
+    expect(result.words).toBe(400);
+    expect(result.minutes).toBe(2);
+  });
+
+  it('should return at least 1 minute', () => {
+    const result = calculateReadingTime('');
+    expect(result.words).toBe(0);
+    expect(result.minutes).toBe(1);
+  });
+
+  it('should ignore HTML tags', () => {
+    const result = calculateReadingTime('<p>Hello</p> <div>World</div>');
+    expect(result.words).toBe(2);
+  });
+});

src/utils/readingTime.ts

@@ -0,0 +1,28 @@
+/**
+ * Calculate reading time for content
+ * Based on average reading speed: ~200 Chinese characters per minute
+ */
+
+export function calculateReadingTime(content: string): { words: number; minutes: number } {
+  // Remove HTML tags and extra whitespace
+  const text = content
+    .replace(/<[^>]*>/g, '')
+    .replace(/\s+/g, ' ')
+    .trim();
+
+  // Count Chinese characters and words
+  // Chinese characters count as 1 word each
+  // English words are counted by splitting on whitespace
+  const chineseChars = (text.match(/[\u4e00-\u9fa5]/g) || []).length;
+  const englishWords = (text.match(/[a-zA-Z0-9]+/g) || []).length;
+
+  const totalWords = chineseChars + englishWords;
+
+  // Average reading speed: 200 characters/words per minute
+  const minutes = Math.ceil(totalWords / 200);
+
+  return {
+    words: totalWords,
+    minutes: Math.max(1, minutes), // At least 1 minute
+  };
+}