Add changenotes.mts flush command

This command will "flush" or move the changenotes in the `unreleased-change-notes` directory to the `[UNRELEASED]` section of the CHANGELOG.md file.

pr-checks/changenotes.mts

@@ -1,11 +1,20 @@
 #!/usr/bin/env npx tsx
 
 import * as fs from "node:fs";
+import { readFileSync } from "node:fs";
 import { pathToFileURL } from "node:url";
 import { parseArgs } from "node:util";
+import path from "path";
 
+import { matter } from "lite-matter";
+
+import {
+  addBodyLinesToUnreleasedSection,
+  parseChangelog,
+  renderChangelog,
+} from "./changelog";
 import { isValidAllChangenoteFiles } from "./changelog/validate.mjs";
-import { CHANGENOTES_DIR } from "./config";
+import { CHANGELOG_FILE, CHANGENOTES_DIR } from "./config";
 
 const entryPoint = process.argv[1];
 if (entryPoint && import.meta.url === pathToFileURL(entryPoint).href) {
@@ -27,6 +36,8 @@ function main(): number {
     case undefined:
     case "help":
       return usage();
+    case "flush":
+      return flush();
     case "validate":
       return validate();
     default:
@@ -36,10 +47,47 @@ function main(): number {
 }
 
 function usage(): number {
-  console.log(`Usage: changenotes.mts validate`);
+  const message =
+    "Usage: changenotes.mts flush\n" +
+    "       changenotes.mts validate\n" +
+    "       changenotes.mts help";
+  console.log(message);
   return 0;
 }
 
+function flush(): number {
+  try {
+    // Get the file paths to our changenotes; these will be useful later.
+    const changenotePaths = fs
+      .readdirSync(CHANGENOTES_DIR)
+      .filter((name) => name !== ".gitkeep")
+      .map((name) => path.join(CHANGENOTES_DIR, name));
+
+    // From the file paths, we read the files to obtain the actual notes themselves.
+    const changenotes = changenotePaths.map((filePath) => {
+      const fileBody = readFileSync(filePath).toString();
+      const { content } = matter(fileBody);
+      return content.trim();
+    });
+
+    const changelogContents = fs.readFileSync(CHANGELOG_FILE).toString();
+    const changelog = parseChangelog(changelogContents);
+    addBodyLinesToUnreleasedSection(changelog, changenotes);
+    fs.writeFileSync(CHANGELOG_FILE, renderChangelog(changelog));
+
+    // Delete changenotes only after successful processing.
+    for (const p of changenotePaths) {
+      fs.unlinkSync(p);
+    }
+
+    return 0;
+  } catch (e) {
+    console.error("Failed to flush changenotes to 'CHANGELOG.md'", e);
+  }
+
+  return 1;
+}
+
 function validate(): number {
   try {
     if (isValidAllChangenoteFiles(fs.readdirSync(CHANGENOTES_DIR))) {