name: Guard custom layer

# The /custom/ layer is a template: in upstream microsoft/BCQuality it stays
# empty by default (README.md + .gitkeep placeholders only). Custom knowledge
# and skills are partner/customer-specific and belong in a fork, never upstream.
#
# This workflow auto-closes any PR that adds or changes content under /custom/
# (anything beyond the allowed template files). It runs only on the upstream
# repo, so forks that legitimately populate /custom/ are unaffected.
#
# pull_request_target is required so the workflow runs with a token that can
# comment on and close the PR (including PRs opened from forks). It only reads
# the PR's file LIST via the API and never checks out or executes PR code, so
# the elevated token is not exposed to untrusted content.

on:
  pull_request_target:
    types: [opened, reopened, synchronize]

permissions:
  contents: read
  pull-requests: write
  issues: write

jobs:
  guard:
    # Never run on forks — a fork's /custom/ content is exactly what's supposed
    # to live there.
    if: github.repository == 'microsoft/BCQuality'
    runs-on: ubuntu-latest
    steps:
      - name: Check out repository
        uses: actions/checkout@v4
        with:
          sparse-checkout: |
            .github/custom-layer-autoclose.md
          sparse-checkout-cone-mode: false

      - name: Close PR if it touches the custom layer
        uses: actions/github-script@v7
        with:
          script: |
            const fs = require('fs');

            // Files under custom/ that ARE allowed to change (the template seed).
            const ALLOWED = new Set([
              'custom/README.md',
            ]);
            // Any .gitkeep under custom/ is also allowed.
            const isAllowed = (p) =>
              ALLOWED.has(p) || /^custom\/.*\.gitkeep$/.test(p) || p === 'custom/.gitkeep';

            const { owner, repo } = context.repo;
            const prNumber = context.payload.pull_request.number;

            const files = await github.paginate(github.rest.pulls.listFiles, {
              owner, repo, pull_number: prNumber, per_page: 100,
            });

            // Offending = added/modified/renamed/copied/changed paths under custom/
            // that are not template files. (We ignore pure deletions.)
            const offending = files
              .filter((f) => f.status !== 'removed')
              .map((f) => f.filename)
              .filter((p) => p.startsWith('custom/') && !isAllowed(p));

            if (offending.length === 0) {
              core.info('No disallowed /custom/ changes found. Nothing to do.');
              return;
            }

            core.warning(`PR #${prNumber} touches the custom layer: ${offending.join(', ')}`);

            const fileList = offending.map((p) => `- \`${p}\``).join('\n');
            let body = fs.readFileSync('.github/custom-layer-autoclose.md', 'utf8');
            body = body
              .replace(/{{AUTHOR}}/g, context.payload.pull_request.user.login)
              .replace(/{{FILES}}/g, fileList);

            await github.rest.issues.createComment({
              owner, repo, issue_number: prNumber, body,
            });

            await github.rest.pulls.update({
              owner, repo, pull_number: prNumber, state: 'closed',
            });

            core.info(`Closed PR #${prNumber}.`);