name: Pyrefly Diff Check

on:
  pull_request:
    paths:
      - 'api/**/*.py'

permissions:
  contents: read

jobs:
  pyrefly-diff:
    runs-on: ubuntu-latest
    permissions:
      contents: read
      issues: write
      pull-requests: write
    steps:
      - name: Checkout PR branch
        uses: actions/checkout@v6
        with:
          fetch-depth: 0

      - name: Setup Python & UV
        uses: astral-sh/setup-uv@v5
        with:
          enable-cache: true

      - name: Install dependencies
        run: uv sync --project api --dev

      - name: Run pyrefly on PR branch
        run: |
          uv run --directory api pyrefly check > /tmp/pyrefly_pr.txt 2>&1 || true

      - name: Checkout base branch
        run: git checkout ${{ github.base_ref }}

      - name: Run pyrefly on base branch
        run: |
          uv run --directory api pyrefly check > /tmp/pyrefly_base.txt 2>&1 || true

      - name: Compute diff
        run: |
          diff /tmp/pyrefly_base.txt /tmp/pyrefly_pr.txt > pyrefly_diff.txt || true

      - name: Save PR number
        run: |
          echo ${{ github.event.pull_request.number }} > pr_number.txt

      - name: Upload pyrefly diff
        uses: actions/upload-artifact@v4
        with:
          name: pyrefly_diff
          path: |
            pyrefly_diff.txt
            pr_number.txt

      - name: Comment PR with pyrefly diff
        if: ${{ github.event.pull_request.head.repo.full_name == github.repository }}
        uses: actions/github-script@v8
        with:
          github-token: ${{ secrets.GITHUB_TOKEN }}
          script: |
            const fs = require('fs');
            let diff = fs.readFileSync('pyrefly_diff.txt', { encoding: 'utf8' });
            const prNumber = context.payload.pull_request.number;

            const MAX_CHARS = 65000;
            if (diff.length > MAX_CHARS) {
              diff = diff.slice(0, MAX_CHARS);
              diff = diff.slice(0, diff.lastIndexOf('\n'));
              diff += '\n\n... (truncated) ...';
            }

            const body = diff.trim()
              ? `### Pyrefly Diff
<details>
<summary>base → PR</summary>

\`\`\`diff
${diff}
\`\`\`
</details>`
              : '### Pyrefly Diff\nNo changes detected.';

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