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:
    # Upstream-only: this fork does not use the PR- label convention.
    if: github.repository == 'element-hq/element-x-android'
    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:
      # Required to comment on the pull request.
      pull-requests: write

    steps:
      - name: Check the pull request
        uses: actions/github-script@3a2844b7e9c422d3c10d287c895573f7108da1b3 # v9.0.0
        with:
          script: |
            // Classes that must not be modified anymore. Add the file name suffix here to freeze a class.
            const FROZEN_CLASSES = [
            ];

            // Only this user is allowed to edit the translation files, since they come from Localazy.
            const TRANSLATION_ALLOW_LIST = ["ElementBot"];

            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
            });
            // Deleted files are not interesting for any of the checks below.
            const paths = files.filter(file => file.status !== "removed").map(file => file.filename);

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

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

            if (paths.length > 50) {
              warnings.push("This pull request seems relatively large. Please consider splitting it into multiple smaller ones.");
            }

            if (pr.title.endsWith("…")) {
              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 single `PR-` label to categorise the changelog entry.");
            }

            for (const frozen of FROZEN_CLASSES) {
              if (paths.some(path => path.endsWith(frozen))) {
                failures.push(`Frozen class \`${frozen}\` has been modified. Please do not modify frozen class.`);
              }
            }

            // Exclude the recorded screenshots, which are legitimately pngs.
            if (paths.some(path => path.toLowerCase().endsWith(".png") && !path.includes("snapshots/images/"))) {
              warnings.push("You seem to have made changes to some images. Please consider using a vector drawable.");
            }

            if (!TRANSLATION_ALLOW_LIST.includes(pr.user.login) && paths.some(path => path.endsWith("translations.xml"))) {
              failures.push("Some translation files have been edited. Only user `ElementBot` (i.e. translations coming from Localazy) is allowed to do that. " +
                "Please read more about translations management [in the doc](https://github.com/element-hq/element-x-android/blob/develop/CONTRIBUTING.md#strings).");
            }

            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.`);
            }