label-title-prefix.yml

name: "Pull Request/Issue Title Prefixer"

on:
  issues:
    types: [labeled]
  pull_request_target:
    types: [labeled]

jobs:
  add_title_prefix:
    name: "Add title prefix based on label"
    runs-on: ubuntu-latest
    permissions:
      issues: write
      pull-requests: write

    steps:
      - uses: actions/github-script@v6
        name: "Update Issue/PR Title"
        with:
          github-token: ${{ secrets.GITHUB_TOKEN }}
          script: |
            const prefixLabels = {
              "documentation": "Docs",
              "build": "Build",
              "translator": "Translator"
            };

            function addTitlePrefix(title, prefix) {
              // Check if title already starts with the prefix
              if (!title.startsWith(prefix + ": ")) {
              // If not, check if the first word is the label case-insensitively
                if (title.match(new RegExp(`^${prefix}`, 'i'))) {
                  // If title has the label case-insensitively, replace it
                  title = title.replace(new RegExp(`^${prefix}`, 'i'), prefix);
                } else {
                  // Otherwise, add the prefix at the beginning
                  title = prefix + ": " + title;
                }
              }
              return title;
            }

            const labelAdded = context.payload.label.name;

            // Check if the issue or PR has the label
            if (labelAdded in prefixLabels) {
              let prefix = prefixLabels[labelAdded];
              switch(context.eventName) {
                case 'issues':
                  github.rest.issues.update({
                    issue_number: context.issue.number,
                    owner: context.repo.owner,
                    repo: context.repo.repo,
                    title: addTitlePrefix(context.payload.issue.title, prefix)
                  });
                  break

                case 'pull_request_target':
                  github.rest.pulls.update({
                    pull_number: context.issue.number,
                    owner: context.repo.owner,
                    repo: context.repo.repo,
                    title: addTitlePrefix(context.payload.pull_request.title, prefix)
                  });
                  break
                default:
                  core.setFailed('Unrecognited eventName: ' + context.eventName);
              }
            }