update-last-modified.yml

name: Update last_modified

on:
  pull_request:
    branches:
      - master
    types:
      - opened
      - synchronize
      - reopened
    paths:
      - "_articles/faq/*.md"

concurrency:
  group: update-last-modified-${{ github.event.pull_request.number }}
  cancel-in-progress: true

permissions:
  contents: write
  pull-requests: read

jobs:
  update-on-master-pr:
    if: github.actor != 'github-actions[bot]' && github.event.pull_request.head.repo.full_name == github.repository
    runs-on: ubuntu-latest
    steps:
      - name: Checkout PR head branch
        uses: actions/checkout@v4
        with:
          ref: ${{ github.event.pull_request.head.ref }}
          fetch-depth: 0

      - name: Collect target files
        id: targets
        shell: bash
        run: |
          set -euo pipefail

          git fetch origin "${{ github.event.pull_request.base.ref }}"

          git diff --name-only "origin/${{ github.event.pull_request.base.ref }}"...HEAD \
            | grep -E '^_articles/faq/[^/]+\.md$' \
            | sort -u > changed_files.txt || true

          count="$(wc -l < changed_files.txt | tr -d ' ')"
          echo "count=$count" >> "$GITHUB_OUTPUT"

      - name: Update front matter
        if: steps.targets.outputs.count != '0'
        shell: bash
        run: |
          set -euo pipefail
          timestamp="$(TZ=UTC date '+%Y-%m-%d %H:%M:%S +0000')"

          while IFS= read -r file; do
            [[ -f "$file" ]] || continue

            TS="$timestamp" perl -0777 -i -pe '
              BEGIN { $ts = $ENV{"TS"}; }

              s{\A---\R(.*?)\R---(?:\R|$)}{
                my $fm = $1;

                if ($fm =~ /^last_modified:.*$/m) {
                  $fm =~ s/^last_modified:.*$/last_modified: $ts/m;
                } elsif ($fm =~ /^date:.*$/m) {
                  $fm =~ s/^(date:.*)$/$1\nlast_modified: $ts/m;
                } else {
                  $fm .= "\nlast_modified: $ts";
                }

                "---\n$fm\n---\n";
              }es;
            ' "$file"
          done < changed_files.txt

      - name: Commit and push to PR branch
        if: steps.targets.outputs.count != '0'
        shell: bash
        run: |
          set -euo pipefail

          if git diff --quiet; then
            echo "No timestamp updates needed."
            exit 0
          fi

          git config user.name "github-actions[bot]"
          git config user.email "41898282+github-actions[bot]@users.noreply.github.com"
          while IFS= read -r file; do
            [[ -f "$file" ]] || continue
            git add "$file"
          done < changed_files.txt
          git commit -m "chore: update last_modified timestamps"
          git pull --rebase origin "${{ github.event.pull_request.head.ref }}"
          git push origin HEAD:${{ github.event.pull_request.head.ref }}