coverage.yml

name: Coverage

on:
  pull_request:
    branches: [ main ]

permissions:
  contents: read
  pull-requests: write

concurrency:
  group: ${{ github.workflow }}-${{ github.ref }}
  cancel-in-progress: true

jobs:
  coverage:
    runs-on: ubuntu-latest
    env:
      BASE_SHA: ${{ github.event.pull_request.base.sha }}
      HEAD_SHA: ${{ github.event.pull_request.head.sha }}
    steps:
      - uses: actions/checkout@v5
        with:
          fetch-depth: 0

      - name: Setup Node.js
        uses: actions/setup-node@v6
        with:
          node-version: '24'
          cache: 'npm'

      - name: Install dependencies
        run: npm ci

      - name: Run coverage on PR
        run: npm run coverage

      - name: Save PR coverage
        run: cp coverage/coverage-summary.json pr-coverage.json

      - name: Run coverage on base
        continue-on-error: true
        id: base_coverage
        run: |
          git fetch --no-tags --prune --depth=1 origin +$BASE_SHA:
          git checkout $BASE_SHA
          npm ci
          if npm run coverage; then
            cp coverage/coverage-summary.json base-coverage.json
            echo "base_coverage_success=true" >> $GITHUB_OUTPUT
          else
            echo "Base coverage failed (likely due to failing tests in base branch)"
            echo "base_coverage_success=false" >> $GITHUB_OUTPUT
            # Create a dummy file so the next step doesn't fail
            echo '{"total":{"statements":{"pct":0},"branches":{"pct":0},"functions":{"pct":0},"lines":{"pct":0}}}' > base-coverage.json
          fi
          git fetch --no-tags --prune --depth=1 origin +$HEAD_SHA:
          git checkout $HEAD_SHA
          npm ci

      - name: Comment coverage
        uses: actions/github-script@v7
        with:
          script: |
            const fs = require('fs');
            const marker = '<!-- coverage-comment -->';
            const pr = JSON.parse(fs.readFileSync('pr-coverage.json', 'utf8')).total;
            let base;
            try {
              base = JSON.parse(fs.readFileSync('base-coverage.json', 'utf8')).total;
            } catch (e) {
              // If base coverage failed, use PR coverage as baseline
              base = pr;
            }

            function row(name, key) {
              const diff = (pr[key].pct - base[key].pct).toFixed(2);
              const sign = diff >= 0 ? '+' : '';
              return `| ${name} | ${pr[key].pct}% | ${sign}${diff}% |`;
            }

            const decreased = ['statements', 'branches', 'functions', 'lines']
              .some(key => pr[key].pct < base[key].pct);

            const summary = decreased
              ? 'Coverage decreased for at least one metric. Please add or update tests to improve coverage.'
              : 'Coverage improved or stayed the same. Great job!';

            const baseFailed = base.statements.pct === 0 && base.branches.pct === 0 && base.functions.pct === 0 && base.lines.pct === 0;
            const comparisonNote = baseFailed 
              ? '⚠️ Could not compare with base branch (base branch has failing tests or coverage issues). Showing PR coverage only.'
              : 'This report compares the PR with the base branch. "Δ" shows how the PR affects each metric.';
            
            const body = [
              marker,
              '### Coverage',
              '',
              comparisonNote,
              '',
              '| Metric | PR |' + (baseFailed ? '' : ' Δ |'),
              '| ------ | --: |' + (baseFailed ? '' : ' ---: |'),
              baseFailed 
                ? `| Statements | ${pr.statements.pct}% |\n| Branches | ${pr.branches.pct}% |\n| Functions | ${pr.functions.pct}% |\n| Lines | ${pr.lines.pct}% |`
                : [row('Statements', 'statements'), row('Branches', 'branches'), row('Functions', 'functions'), row('Lines', 'lines')].join('\n'),
              '',
              baseFailed ? '✅ Coverage thresholds met! All tests passing.' : summary,
              '',
              'Run `npm run coverage` locally for detailed reports and target untested areas to raise these numbers.'
            ].join('\n');

            const { owner, repo } = context.repo;
            const issue_number = context.issue.number;

            const comments = await github.rest.issues.listComments({ owner, repo, issue_number });
            const previous = comments.data.find(c => c.body.includes(marker));
            if (previous) {
              await github.rest.issues.deleteComment({ owner, repo, comment_id: previous.id });
            }

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