action.yml

name: "Branch out-of-sync notifier"
description: "Comments on a given PR if the base branch is out of sync with the target one."
branding:
  icon: git-branch
  color: orange

inputs:
  base-ref:
    description: "The base git reference, used for comparison."
    default: ${{ github.event.pull_request.base.ref }}
    required: true
  head-ref:
    description: "The head git reference, used for comparison."
    default: ${{ github.event.pull_request.head.ref }}
    required: true
  request-owner:
    description: "The owner of the pull request"
    default: ${{ github.event.pull_request.user.login }}
    required: true
  request-number:
    descripton: "The pull request number"
    default: ${{ github.event.pull_request.number }}
    required: true
  no-sync-label:
    description: "The label value, used for tagging PRs that shouldn't be checked"
    default: 'no-branch-sync'
    required: false

runs:
  using: "composite"
  steps:
    - name: Checkout repository
      uses: actions/checkout@v4
      with:
        fetch-depth: 0
        submodules: true
        clean: false

    - name: Check if no-sync label has been applied
      uses: actions/github-script@v7
      id: "check-for-no-sync-label"
      with:
        script: |
          const labels = await github.paginate(github.rest.issues.listLabelsOnIssue, {
              issue_number: ${{ inputs.request-number }},
              owner: context.repo.owner,
              repo: context.repo.repo,
          });

          const projectedLabels = labels?.map(l => l.name);
          const isNoSyncLabelApplied = projectedLabels.includes('${{ inputs.no-sync-label }}');
          return isNoSyncLabelApplied;

    - name: Compare branches
      id: "compare-branches"
      if: steps.check-for-no-sync-label.outputs.result == 'false'
      shell: bash
      run: |
        git fetch --all
        echo "behind=$(git rev-list --count origin/${{ inputs.head-ref }}..origin/${{ inputs.base-ref }})" >> $GITHUB_OUTPUT
        echo "ahead=$(git rev-list --count origin/${{ inputs.base-ref }}..origin/${{ inputs.head-ref }})" >> $GITHUB_OUTPUT

    - name: Remove existing comments
      uses: actions/github-script@v7
      if: steps.check-for-no-sync-label.outputs.result == 'false'
      env:
        # Top level env. variables are not supported in composite actions :(
        SYNC_BOT_TITLE: "Branch Sync Notifier"
        BOT_LOGIN: "github-actions[bot]"
      with:
        script: |
          const pullRequestComments = await github.paginate(github.rest.issues.listComments, {
              issue_number: ${{ inputs.request-number }},
              owner: context.repo.owner,
              repo: context.repo.repo,
          });

          const botComments = pullRequestComments.filter(c => {
              return c.user.login === '${{ env.BOT_LOGIN }}' && c.body.includes('${{ env.SYNC_BOT_TITLE }}');
          });

          botComments.forEach(async comment => {
              await github.rest.issues.deleteComment({
                comment_id: comment.id,
                owner: context.repo.owner,
                repo: context.repo.repo
              });
          });

    - name: Comment if head branch is out of sync
      uses: actions/github-script@v7
      if: steps.compare-branches.outputs.behind > 0
      env:
        SYNC_BOT_TITLE: "Branch Sync Notifier"
      with:
        script: |
          const body = `# ${{ env.SYNC_BOT_TITLE }} :bell: 

          ### Hey, @${{ inputs.request-owner }}! :wave:
          ### Your branch is out of sync with the PR's target branch. 
          ### Please rebase it on top of the latest changes from \`${{ inputs.base-ref }}\` or merge them. :sun_with_face:

          **Run: [${{ github.run_number }}](${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }}) :rabbit2:** 
          **Attempt: № \`${{ github.run_attempt }}\` :eyes:**
          `;

          github.rest.issues.createComment({
            issue_number: ${{ inputs.request-number }},
            owner: context.repo.owner,
            repo: context.repo.repo,
            body: body
          })