create/.github/workflows/weekly-compare-link.yml

name: Weekly compare link to release notes

on:
  release:
    types: [published]   # run automatically when a (pre-)release is published
  workflow_dispatch:      # allow manual runs too
    inputs:
      current_tag:
        description: "Weekly tag (e.g., weekly-2026.01.07). Leave empty to auto-detect latest weekly pre-release."
        required: false
      dry_run:
        description: "Only compute; do not update the release body."
        required: false
        type: boolean
        default: false

permissions:
  contents: write        # required to PATCH the release body

jobs:
  update-notes:
    runs-on: ubuntu-latest
    steps:
      - name: Inject compare link into weekly release notes
        uses: actions/github-script@v7
        env:
          # Pass manual inputs via env for convenience
          CURRENT_TAG: ${{ github.event.inputs.current_tag }}
          DRY_RUN: ${{ github.event.inputs.dry_run }}
          PLACEHOLDER: "<!--DIFF_LINK-->"
        with:
          script: |
            // Updates the current weekly release notes with a compare link to the previous weekly.
            // Works for both release-published events and manual (workflow_dispatch) runs.
            const owner = context.repo.owner;
            const repo  = context.repo.repo;

            const rx = /^weekly-(\d{4})\.(\d{2})\.(\d{2})$/;

            // Determine currentTag:
            // 1) Manual input via workflow_dispatch (env.CURRENT_TAG)
            // 2) Tag from release event payload
            // 3) Fallback: newest weekly pre-release
            let currentTag = process.env.CURRENT_TAG || (context.payload?.release?.tag_name) || null;

            async function detectLatestWeeklyTag() {
              const releases = await github.paginate(github.rest.repos.listReleases, { owner, repo, per_page: 100 });
              const cand = releases.find(r => r.prerelease && typeof r.tag_name === 'string' && rx.test(r.tag_name));
              return cand?.tag_name || null;
            }

            if (!currentTag) {
              currentTag = await detectLatestWeeklyTag();
            }

            if (!currentTag || !rx.test(currentTag)) {
              core.info(`No weekly tag detected or tag format mismatch ('${currentTag}'). Skipping.`);
              return;
            }

            // Resolve the current release object
            let curRel;
            try {
              const { data } = await github.rest.repos.getReleaseByTag({ owner, repo, tag: currentTag });
              curRel = data;
            } catch (e) {
              core.setFailed(`No release for tag ${currentTag}: ${e.message}`);
              return;
            }

            // If event is a normal release (not pre-release), skip automatically-run case;
            // but allow manual override (manual runs can patch any weekly tag).
            const isManual = context.eventName === 'workflow_dispatch';
            if (!isManual && !curRel.prerelease) {
              core.info('Current release is not a pre-release; skipping (auto run).');
              return;
            }

            // Helpers
            const toPrevWeeklyTag = (tag) => {
              const [, y, m, d] = tag.match(rx);
              const dt = new Date(Date.UTC(+y, +m - 1, +d));
              const prev = new Date(dt.getTime() - 7 * 24 * 3600 * 1000); // minus 7 days
              const iso = prev.toISOString().slice(0, 10); // YYYY-MM-DD
              return `weekly-${iso.replace(/-/g, '.')}`;   // weekly-YYYY.MM.DD
            };
            const ymdKey = (t) => t.replace(rx, '$1$2$3'); // YYYYMMDD

            async function tagExists(tag) {
              try {
                await github.rest.git.getRef({ owner, repo, ref: `tags/${tag}` });
                return true;
              } catch {
                return false;
              }
            }

            // Compute previous weekly deterministically, then fall back if needed
            let prevTag = toPrevWeeklyTag(currentTag);
            if (!(await tagExists(prevTag))) {
              core.info(`Computed previous tag ${prevTag} not found; scanning older weeklies...`);
              const releases = await github.paginate(github.rest.repos.listReleases, { owner, repo, per_page: 100 });
              const curKey = ymdKey(currentTag);
              const older = releases
                .filter(r => r.prerelease && typeof r.tag_name === 'string' && rx.test(r.tag_name))
                .map(r => ({ tag: r.tag_name, key: ymdKey(r.tag_name) }))
                .filter(x => x.key < curKey)
                .sort((a, b) => b.key.localeCompare(a.key)); // newest older first
              if (!older.length) {
                core.info('No older weekly found; nothing to do.');
                return;
              }
              prevTag = older[0].tag;
            }

            const compareUrl = `https://github.com/${owner}/${repo}/compare/${prevTag}...${currentTag}`;
            const head = `**Changes since last weekly (${prevTag} → ${currentTag}):**\n${compareUrl}\n`;

            if (process.env.DRY_RUN === 'true') {
              core.info(`[DRY RUN] Would update release ${currentTag} with: ${compareUrl}`);
              return;
            }

            // Idempotent body update
            let body = curRel.body || '';
            if (body.includes(compareUrl)) {
              core.info('Compare URL already present; done.');
              return;
            }
            const placeholder = process.env.PLACEHOLDER || '<!--DIFF_LINK-->';
            if (body.includes(placeholder)) {
              body = body.replace(placeholder, compareUrl);
            } else if (/\*\*Changes since last weekly:/i.test(body)) {
              body = body.replace(/\*\*Changes since last weekly:[^\n]*\n?/i, head + '\n');
            } else {
              body += (body.endsWith('\n') ? '\n' : '\n\n') + head;
            }

            await github.rest.repos.updateRelease({ owner, repo, release_id: curRel.id, body });
            core.info(`Release notes updated with compare link: ${compareUrl}`);