Auto-update last updated dates

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name: Update last updated date
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# Trigger this workflow when PRs are opened or updated
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on:
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  pull_request:
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    types: [opened, synchronize]
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    branches:
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      - main  # Adjust to match your main branch name
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jobs:
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  update-last-updated:
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    runs-on: ubuntu-latest
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    # No token can push to a contributor's fork, so the push would fail.
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    # Skip fork PRs instead.
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    if: github.event.pull_request.head.repo.full_name == github.repository
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    permissions:
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      contents: write         # Required to commit changes
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      pull-requests: write    # Required to update the PR
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    steps:
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      # Step 1: Check out the PR branch
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      - name: Checkout repository
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        uses: actions/checkout@v4
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        with:
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          ref: ${{ github.head_ref }}  # Check out the PR's source branch
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          fetch-depth: 0
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          token: ${{ secrets.DOCS_BOT_TOKEN }}  # A PAT, not GITHUB_TOKEN
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      # Step 2: Identify which MDX files changed in this PR
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      - name: Get changed MDX files
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        id: changed-files
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        uses: tj-actions/changed-files@v45
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        with:
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          files: |
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            **/*.mdx  # Only track changes to .mdx files
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      # Step 3: Update the last-updated field in each changed MDX file
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      - name: Update last-updated frontmatter
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        if: steps.changed-files.outputs.any_changed == 'true'
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        run: |
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          # Generate current date in "Month Day, Year" format (e.g., "December 11, 2025")
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          # Modify the date format here if you prefer a different style
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          CURRENT_DATE=$(date +"%B %-d, %Y")
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          echo "Current date: $CURRENT_DATE"
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          # Process each changed MDX file
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          for file in ${{ steps.changed-files.outputs.all_changed_files }}; do
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            echo "Processing: $file"
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            # Skip if file was deleted or doesn't exist
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            if [ ! -f "$file" ]; then
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              echo "File not found, skipping: $file"
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              continue
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            fi
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            # Check if file has frontmatter (must start with ---)
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            if ! head -1 "$file" | grep -q "^---"; then
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              echo "No frontmatter found, skipping: $file"
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              continue
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            # If file already has a last-updated field, update it
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            elif grep -q "^last-updated:" "$file"; then
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              echo "Updating existing last-updated field"
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              sed -i "s/^last-updated:.*$/last-updated: $CURRENT_DATE/" "$file"
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            # If file has frontmatter but no last-updated field, add it
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            else
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              echo "Adding last-updated field to existing frontmatter"
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              # This awk command inserts the last-updated field just before the closing ---
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              awk -v date="$CURRENT_DATE" '
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                BEGIN { in_frontmatter=0; added=0 }
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                NR==1 && /^---$/ { in_frontmatter=1; print; next }
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                in_frontmatter && /^---$/ && !added { print "last-updated: " date; added=1; print; in_frontmatter=0; next }
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                { print }
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              ' "$file" > "${file}.tmp" && mv "${file}.tmp" "$file"
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            fi
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          done
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      # Step 4: Commit and push the updated files back to the PR
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      - name: Commit changes
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        if: steps.changed-files.outputs.any_changed == 'true'
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        run: |
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          git config --local user.email "github-actions[bot]@users.noreply.github.com"
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          git config --local user.name "github-actions[bot]"
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          git add -A
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          # Only commit if there are actual changes
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          if git diff --staged --quiet; then
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            echo "No changes to commit"
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          else
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            git commit -m "chore: update last-updated date in MDX files"
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            git push
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          fi