feat(theme): add normalize page title markdown plugin

theme/src/node/plugins/markdown-title.ts

@@ -0,0 +1,46 @@
+import type { Plugin } from 'vuepress/core'
+import type { MarkdownEnv } from 'vuepress/markdown'
+
+const REG_HEADING = /^#\s*?(\S.*)?\n/
+
+export function markdownTitlePlugin(): Plugin {
+  return {
+    name: '@vuepress-plume/plugin-markdown-title',
+
+    extendsMarkdown(md) {
+      const render = md.render
+      md.render = (source, env: MarkdownEnv) => {
+        if (!env.filePathRelative)
+          return render(source, env)
+
+        let { matter, content } = parseSource(source.trim())
+        let title = ''
+        content = content.trim().replace(REG_HEADING, (_, match) => {
+          title = match.trim()
+          return ''
+        })
+        source = `${matter}\n${content}`
+        const result = render(source, env)
+        if (title)
+          env.title = title
+        return result
+      }
+    },
+  }
+}
+
+function parseSource(source: string) {
+  const char = '---'
+
+  if (!source.startsWith(char)) {
+    return { matter: '', content: source }
+  }
+  else {
+    const end = source.indexOf(`\n${char}`)
+    const len = char.length + 1
+    return {
+      matter: source.slice(0, end + len),
+      content: source.slice(end + len),
+    }
+  }
+}