update-changelog.yaml

name: Update CHANGELOG.md

on:
  pull_request:
    branches:
      - main
    types: [closed]

concurrency:
  group: update-changelog

jobs:
  update-changelog:
    runs-on: ubuntu-22.04
    name: Update CHANGELOG.md
    if: github.event.pull_request.merged == true
    steps:
      - uses: actions/checkout@v4
      - name: Update CHANGELOG.md
        id: changelog
        uses: actions/github-script@v7
        with:
          script: |
            // Fetches an issue (pull request) information.
            const {promises: fs} = require('fs');
            const {data: issue} = await github.rest.issues.get({
              ...context.repo,
              issue_number: context.issue.number,
            });
            console.log(issue);
            const {user, pull_request: pull} = issue;

            // Reads the current `CHANGELOG.md`.
            let changelog = await fs.readFile('CHANGELOG.md', 'utf-8');

            // Exatracts `# dev` section from the `CHANGELOG.md`.
            const devMatch = changelog.match(/^# dev\n\n([^]*?)(?=\n# )\n/);
            let devSection = '';
            if (devMatch !== null) {
              changelog = changelog.slice(devMatch[0].length);
              devSection = devMatch[0];
            }
            console.log(devSection);

            // Extracts each update subsection from `# dev` section.
            const updateLists = {
              feature: { category: 'New Features' },
              change: { category: 'Changes' },
              fix: { category: 'Fixes' },
              misc: { category: 'Misc' },
            };
            for (const label of Object.keys(updateLists)) {
              const subsection = `\n${updateLists[label].category}:\n\n`;
              const index = devSection.indexOf(subsection);
              if (index === -1) {
                updateLists[label].updates = [];
                continue;
              }

              const endIndex = devSection.indexOf('\n\n', index + subsection.length);
              updateLists[label].updates = devSection.slice(index + subsection.length, endIndex).split('\n');
            }
            console.log(updateLists);

            // Inserts a new line for this update to the update list specified by a label.
            const newLine = `- [#${issue.number}](${pull.html_url}) ${issue.title} ([@${user.login}](${user.html_url}))`;
            let hasUpdate = false;
            for (const label of issue.labels) {
              console.log(label);
              if (updateLists[label.name]) {
                updateLists[label.name].updates.push(newLine);
                hasUpdate = true;
              }
            }

            core.setOutput('has_update', hasUpdate);
            if (!hasUpdate) return;

            let newDevSection = '# dev\n';
            for (const label of Object.keys(updateLists)) {
              if (updateLists[label].updates.length === 0) {
                continue;
              }

              newDevSection += '\n';
              newDevSection += `${updateLists[label].category}:\n`;
              newDevSection += `\n`;
              for (const update of updateLists[label].updates) {
                newDevSection += `${update}\n`;
              }
            }
            console.log(newDevSection);

            // Updates the `CHANGELOG.md`.
            changelog = `${newDevSection}\n${changelog}`;
            await fs.writeFile('CHANGELOG.md', changelog);
      - name: Commit a new `CHANGELOG.md`
        if: steps.changelog.outputs.has_update == 'true'
        run: |
          git config --local user.name "MakeNowJust bot"
          git config --local user.email "make.just.on@gmail.com"
          git add .
          git commit -m "Update CHANGELOG.md"
          git push origin main