feat: import code snippet with region (#237)

docs/guide/markdown.md

@@ -324,6 +324,70 @@ module.exports = {
   }
 </style>
 
+## Import Code Snippets
+
+You can import code snippets from existing files via following syntax:
+
+```md
+<<< @/filepath
+```
+
+It also supports [line highlighting](#line-highlighting-in-code-blocks):
+
+```md
+<<< @/filepath{highlightLines}
+```
+
+**Input**
+
+```md
+<<< @/snippets/snippet.js{2}
+```
+
+**Code file**
+
+<!--lint disable strong-marker-->
+
+<<< @/snippets/snippet.js
+
+<!--lint enable strong-marker-->
+
+**Output**
+
+<!--lint disable strong-marker-->
+
+<<< @/snippets/snippet.js{2}
+
+<!--lint enable strong-marker-->
+
+::: tip
+The value of `@` corresponds to `process.cwd()`.
+:::
+
+You can also use a [VS Code region](https://code.visualstudio.com/docs/editor/codebasics#_folding) to only include the corresponding part of the code file. You can provide a custom region name after a `#` following the filepath (`snippet` by default):
+
+**Input**
+
+```md
+<<< @/snippets/snippet-with-region.js{1}
+```
+
+**Code file**
+
+<!--lint disable strong-marker-->
+
+<<< @/snippets/snippet-with-region.js
+
+<!--lint enable strong-marker-->
+
+**Output**
+
+<!--lint disable strong-marker-->
+
+<<< @/snippets/snippet-with-region.js#snippet{1}
+
+<!--lint enable strong-marker-->
+
 ## Advanced Configuration
 
 VitePress uses [markdown-it](https://github.com/markdown-it/markdown-it) as the Markdown renderer. A lot of the extensions above are implemented via custom plugins. You can further customize the `markdown-it` instance using the `markdown` option in `.vitepress/config.js`:

docs/snippets/snippet-with-region.js

@@ -0,0 +1,7 @@
+// #region snippet
+function foo() {
+  // ..
+}
+// #endregion snippet
+
+export default foo

docs/snippets/snippet.js

@@ -0,0 +1,3 @@
+export default function () {
+  // ..
+}

src/node/markdown/plugins/snippet.ts

@@ -1,7 +1,83 @@
 import fs from 'fs'
+import path from 'path'
 import MarkdownIt from 'markdown-it'
 import { RuleBlock } from 'markdown-it/lib/parser_block'
 
+function dedent(text: string) {
+  const wRegexp = /^([ \t]*)(.*)\n/gm
+  let match
+  let minIndentLength = null
+
+  while ((match = wRegexp.exec(text)) !== null) {
+    const [indentation, content] = match.slice(1)
+    if (!content) continue
+
+    const indentLength = indentation.length
+    if (indentLength > 0) {
+      minIndentLength =
+        minIndentLength !== null
+          ? Math.min(minIndentLength, indentLength)
+          : indentLength
+    } else break
+  }
+
+  if (minIndentLength) {
+    text = text.replace(
+      new RegExp(`^[ \t]{${minIndentLength}}(.*)`, 'gm'),
+      '$1'
+    )
+  }
+
+  return text
+}
+
+function testLine(
+  line: string,
+  regexp: RegExp,
+  regionName: string,
+  end: boolean = false
+) {
+  const [full, tag, name] = regexp.exec(line.trim()) || []
+
+  return (
+    full &&
+    tag &&
+    name === regionName &&
+    tag.match(end ? /^[Ee]nd ?[rR]egion$/ : /^[rR]egion$/)
+  )
+}
+
+function findRegion(lines: Array<string>, regionName: string) {
+  const regionRegexps = [
+    /^\/\/ ?#?((?:end)?region) ([\w*-]+)$/, // javascript, typescript, java
+    /^\/\* ?#((?:end)?region) ([\w*-]+) ?\*\/$/, // css, less, scss
+    /^#pragma ((?:end)?region) ([\w*-]+)$/, // C, C++
+    /^<!-- #?((?:end)?region) ([\w*-]+) -->$/, // HTML, markdown
+    /^#((?:End )Region) ([\w*-]+)$/, // Visual Basic
+    /^::#((?:end)region) ([\w*-]+)$/, // Bat
+    /^# ?((?:end)?region) ([\w*-]+)$/ // C#, PHP, Powershell, Python, perl & misc
+  ]
+
+  let regexp = null
+  let start = -1
+
+  for (const [lineId, line] of lines.entries()) {
+    if (regexp === null) {
+      for (const reg of regionRegexps) {
+        if (testLine(line, reg, regionName)) {
+          start = lineId + 1
+          regexp = reg
+          break
+        }
+      }
+    } else if (testLine(line, regexp, regionName, true)) {
+      return { start, end: lineId, regexp }
+    }
+  }
+
+  return null
+}
+
 export const snippetPlugin = (md: MarkdownIt, root: string) => {
   const parser: RuleBlock = (state, startLine, endLine, silent) => {
     const CH = '<'.charCodeAt(0)
@@ -24,23 +100,78 @@ export const snippetPlugin = (md: MarkdownIt, root: string) => {
 
     const start = pos + 3
     const end = state.skipSpacesBack(max, pos)
-    const rawPath = state.src.slice(start, end).trim().replace(/^@/, root)
-    const filename = rawPath.split(/{/).shift()!.trim()
-    const content = fs.existsSync(filename)
-      ? fs.readFileSync(filename).toString()
-      : 'Not found: ' + filename
-    const meta = rawPath.replace(filename, '')
+
+    /**
+     * raw path format: "/path/to/file.extension#region {meta}"
+     *    where #region and {meta} are optional
+     *
+     * captures: ['/path/to/file.extension', 'extension', '#region', '{meta}']
+     */
+    const rawPathRegexp = /^(.+(?:\.([a-z]+)))(?:(#[\w-]+))?(?: ?({\d+(?:[,-]\d+)*}))?$/
+
+    const rawPath = state.src
+      .slice(start, end)
+      .trim()
+      .replace(/^@/, root)
+      .trim()
+    const [filename = '', extension = '', region = '', meta = ''] = (
+      rawPathRegexp.exec(rawPath) || []
+    ).slice(1)
 
     state.line = startLine + 1
 
     const token = state.push('fence', 'code', 0)
-    token.info = filename.split('.').pop() + meta
-    token.content = content
+    token.info = extension + meta
+
+    // @ts-ignore
+    token.src = path.resolve(filename) + region
     token.markup = '```'
     token.map = [startLine, startLine + 1]
 
     return true
   }
 
+  const fence = md.renderer.rules.fence!
+
+  md.renderer.rules.fence = (...args) => {
+    const [tokens, idx, , { loader }] = args
+    const token = tokens[idx]
+    // @ts-ignore
+    const tokenSrc = token.src
+    const [src, regionName] = tokenSrc ? tokenSrc.split('#') : ['']
+
+    if (src) {
+      if (loader) {
+        loader.addDependency(src)
+      }
+      const isAFile = fs.lstatSync(src).isFile()
+      if (fs.existsSync(src) && isAFile) {
+        let content = fs.readFileSync(src, 'utf8')
+
+        if (regionName) {
+          const lines = content.split(/\r?\n/)
+          const region = findRegion(lines, regionName)
+
+          if (region) {
+            content = dedent(
+              lines
+                .slice(region.start, region.end)
+                .filter((line: string) => !region.regexp.test(line.trim()))
+                .join('\n')
+            )
+          }
+        }
+
+        token.content = content
+      } else {
+        token.content = isAFile
+          ? `Code snippet path not found: ${src}`
+          : `Invalid code snippet option`
+        token.info = ''
+      }
+    }
+    return fence(...args)
+  }
+
   md.block.ruler.before('fence', 'snippet', parser)
 }