feat(sitemap): improve sitemap generation with git last modified dates

Add git last modified date tracking for sitemap URLs to provide more accurate lastmod timestamps
Only write sitemap file when content actually changes to avoid unnecessary updates

scripts/generate-sitemap.mjs

@@ -7,6 +7,7 @@
 import fs from 'fs'
 import path from 'path'
 import { fileURLToPath } from 'url'
+import { execSync } from 'child_process'
 
 const __filename = fileURLToPath(import.meta.url)
 const __dirname = path.dirname(__filename)
@@ -72,10 +73,38 @@ function mdPathToUrl(mdPath, locale) {
   return `${siteUrl}/${locale}/${urlPath}${urlPath ? '/' : ''}`
 }
 
-// 生成 sitemap XML
-function generateSitemap(urls) {
-  const now = new Date().toISOString()
+function getGitLastModified(filePath) {
+  try {
+    const result = execSync(`git log -1 --format="%aI" -- "${filePath}"`, {
+      cwd: path.resolve(__dirname, '..'),
+      encoding: 'utf-8',
+      stdio: ['pipe', 'pipe', 'pipe']
+    }).trim()
+    if (result) {
+      return result
+    }
+  } catch {
+    // 文件可能是新文件或不在 git 中
+  }
+  const stats = fs.statSync(filePath)
+  return stats.mtime.toISOString()
+}
 
+function getLatestModTime(files) {
+  let latest = '1970-01-01T00:00:00.000Z'
+  for (const file of files) {
+    const fullPath = path.join(docsDir, file.locale, file.relativePath)
+    if (fs.existsSync(fullPath)) {
+      const modTime = getGitLastModified(fullPath)
+      if (modTime > latest) {
+        latest = modTime
+      }
+    }
+  }
+  return latest
+}
+
+function generateSitemap(urls) {
   let xml = '<?xml version="1.0" encoding="UTF-8"?>\n'
   xml += '<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9"\n'
   xml += '         xmlns:xhtml="http://www.w3.org/1999/xhtml">\n'
@@ -83,11 +112,10 @@ function generateSitemap(urls) {
   for (const urlInfo of urls) {
     xml += '  <url>\n'
     xml += `    <loc>${escapeXml(urlInfo.loc)}</loc>\n`
-    xml += `    <lastmod>${now}</lastmod>\n`
+    xml += `    <lastmod>${urlInfo.lastmod}</lastmod>\n`
     xml += `    <changefreq>weekly</changefreq>\n`
     xml += `    <priority>${urlInfo.priority.toFixed(1)}</priority>\n`
 
-    // 添加 hreflang alternates
     for (const alternate of urlInfo.alternates) {
       xml += `    <xhtml:link rel="alternate" hreflang="${alternate.hreflang}" href="${escapeXml(alternate.href)}"/>\n`
     }
@@ -136,7 +164,8 @@ function main() {
     const urlInfo = {
       loc: '',
       priority: getPriority(baseFile),
-      alternates: []
+      alternates: [],
+      sourceFiles: []
     }
 
     // 为每个语言版本生成 alternate
@@ -151,6 +180,7 @@ function main() {
           hreflang: getHreflangCode(locale),
           href: url
         })
+        urlInfo.sourceFiles.push({ locale, relativePath: baseFile })
 
         // 设置主要语言版本为 zh-cn
         if (locale === 'zh-cn') {
@@ -165,31 +195,51 @@ function main() {
       if (!urlInfo.loc) {
         urlInfo.loc = urlInfo.alternates[0].href
       }
+      urlInfo.lastmod = getLatestModTime(urlInfo.sourceFiles)
       allUrls.push(urlInfo)
     }
   }
 
   // 添加首页
   const homeAlternates = []
+  const homeSourceFiles = []
   for (const locale of locales) {
     homeAlternates.push({
       hreflang: getHreflangCode(locale),
       href: `${siteUrl}/${locale}/`
     })
+    const indexPath = path.join(docsDir, locale, 'index.md')
+    if (fs.existsSync(indexPath)) {
+      homeSourceFiles.push({ locale, relativePath: 'index.md' })
+    }
   }
   allUrls.unshift({
     loc: `${siteUrl}/zh-cn/`,
     priority: 1.0,
-    alternates: homeAlternates
+    alternates: homeAlternates,
+    sourceFiles: homeSourceFiles,
+    lastmod: getLatestModTime(homeSourceFiles)
   })
 
   console.log(`🌐 Generating sitemap with ${allUrls.length} URLs...`)
 
   const sitemapXml = generateSitemap(allUrls)
   const outputPath = path.join(publicDir, 'sitemap.xml')
-  fs.writeFileSync(outputPath, sitemapXml, 'utf-8')
 
+  let shouldWrite = true
+  if (fs.existsSync(outputPath)) {
+    const existingXml = fs.readFileSync(outputPath, 'utf-8')
+    if (existingXml === sitemapXml) {
+      shouldWrite = false
+      console.log(`⏭️  Sitemap unchanged, skipping write`)
+    }
+  }
+
+  if (shouldWrite) {
+    fs.writeFileSync(outputPath, sitemapXml, 'utf-8')
     console.log(`✅ Sitemap generated at ${outputPath}`)
+  }
+
   console.log(`📊 Statistics:`)
   console.log(`   - Total URLs: ${allUrls.length}`)
   console.log(`   - Locales: ${locales.length}`)