name: PR Checks

on:
  # Privilege escalation necessary to comment on pull requests from forks.
  # 🚨 We must not check out or execute any code here, and be careful around use of user-controlled inputs.
  pull_request_target: # zizmor: ignore[dangerous-triggers]
    types: [opened, reopened, edited, synchronize, labeled, unlabeled]

permissions: {}

jobs:
  pr-checks:
    name: PR Checks
    runs-on: ubuntu-latest
    timeout-minutes: 5

    concurrency:
      # Only allow a single run of this workflow on each branch, automatically cancelling older runs.
      group: ${{ format('pr-checks-{0}', github.ref) }}
      cancel-in-progress: true

    permissions:
      pull-requests: write

    steps:
      - name: Check the pull request
        uses: actions/github-script@3a2844b7e9c422d3c10d287c895573f7108da1b3 # v9.0.0
        with:
          script: |
            const pr = context.payload.pull_request;
            const body = pr.body ?? "";

            const files = await github.paginate(github.rest.pulls.listFiles, {
              owner: context.repo.owner,
              repo: context.repo.repo,
              pull_number: pr.number
            });
            const paths = files.map(file => file.filename.toLowerCase());

            const warnings = [];
            const failures = [];

            if (pr.additions > 1000) {
              warnings.push("This pull request seems relatively large. Please consider splitting it into multiple smaller ones.");
            }

            if (!body) {
              warnings.push("Please provide a description for this PR.");
            }

            if (paths.some(path => path.includes("/view")) && !body.includes("user-attachments")) {
              warnings.push("You seem to have made changes to views. Please consider adding screenshots.");
            }

            if (paths.some(path => path.includes(".xcassets") && path.endsWith(".png"))) {
              warnings.push("You seem to have made changes to some resource images. Please consider using an SVG or PDF.");
            }

            if (pr.title.endsWith("…") || /^(Fixes|Fix) #\d+/.test(pr.title) || /^\w+\(\w+\):/.test(pr.title)) {
              failures.push("Please provide a complete title that can be used as a changelog entry.");
            }

            if (pr.labels.filter(label => label.name.startsWith("pr-")).length !== 1) {
              failures.push("Please add a `pr-` label to categorise the changelog entry.");
            }

            warnings.forEach(warning => core.warning(warning));
            failures.forEach(failure => core.error(failure));

            // Keep a single comment up to date rather than adding a new one on every run.
            const marker = "<!-- pr-checks -->";
            const comments = await github.paginate(github.rest.issues.listComments, {
              owner: context.repo.owner,
              repo: context.repo.repo,
              issue_number: pr.number
            });
            const existing = comments.find(comment => comment.body.includes(marker));

            if (warnings.length || failures.length) {
              const lines = [...failures.map(failure => `- ❌ ${failure}`),
                             ...warnings.map(warning => `- ⚠️ ${warning}`)];
              const commentBody = `${marker}\n### PR Checks\n\n${lines.join("\n")}`;

              if (existing) {
                await github.rest.issues.updateComment({
                  owner: context.repo.owner,
                  repo: context.repo.repo,
                  comment_id: existing.id,
                  body: commentBody
                });
              } else {
                await github.rest.issues.createComment({
                  owner: context.repo.owner,
                  repo: context.repo.repo,
                  issue_number: pr.number,
                  body: commentBody
                });
              }
            } else if (existing) {
              await github.rest.issues.deleteComment({
                owner: context.repo.owner,
                repo: context.repo.repo,
                comment_id: existing.id
              });
            }

            if (failures.length) {
              core.setFailed(`${failures.length} check(s) failed, see the comment on the pull request.`);
            }