ci: check README table of content

.github/workflows/tests.yml

@@ -20,6 +20,7 @@ jobs:
       - run: npm ci
       - run: npm run lint
       - run: npm run format
+      - run: node tools/toc.js check
       - run: npx markdown-link-check -p README.md
 
   integration:

tools/toc.js

@@ -0,0 +1,65 @@
+const { readFileSync: read, writeFileSync: write } = require("fs")
+
+const action = process.argv[2]
+
+switch (action) {
+  case "check": {
+    const currentToc = splitReadme()[1]
+    if (currentToc !== generateToc()) {
+      console.log("Table of content is outdated. Use 'write' to update it.")
+      process.exit(1)
+    } else {
+      console.log("Table of content is up to date.")
+    }
+    break
+  }
+
+  case "write": {
+    const [start, _, end] = splitReadme()
+    writeReadme(start + generateToc() + end)
+    break
+  }
+
+  default:
+    console.log(
+      `${process.argv[1]} takes one argument, either "check" or "write"`
+    )
+    process.exit(1)
+}
+
+function readReadme() {
+  return read("README.md", { encoding: "utf-8" })
+}
+
+function writeReadme(content) {
+  write("README.md", content, { encoding: "utf-8" })
+}
+
+function splitReadme() {
+  const content = readReadme()
+  let startTocIndex = content.indexOf("\n\n") + 2
+  let endTocIndex = content.indexOf("\n\n", startTocIndex)
+
+  return [
+    content.slice(0, startTocIndex),
+    content.slice(startTocIndex, endTocIndex),
+    content.slice(endTocIndex),
+  ]
+}
+
+function generateToc() {
+  return readReadme()
+    .split("\n")
+    .flatMap((line) => {
+      const level = line.match(/^#*/)[0].length
+      if (!level) return []
+
+      const title = line.slice(level + 1)
+      const urlHash = title
+        .toLowerCase()
+        .replace(/ /g, "-")
+        .replace(/[^-a-z0-9]/g, "")
+      return `${"  ".repeat(level - 2)}- [${title}](#${urlHash})`
+    })
+    .join("\n")
+}