# Copyright 2025 Google LLC.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

name: Auto Update PR

on:
  push:
    branches: [main]
  schedule:
    # Run daily at 2 AM UTC to catch stale PRs
    - cron: '0 2 * * *'
  workflow_dispatch:
    inputs:
      pr_number:
        description: 'PR number to update (optional, updates all if not specified)'
        required: false
        type: string

permissions:
  contents: write  # Required for updateBranch API
  pull-requests: write
  issues: write

jobs:
  update-prs:
    runs-on: ubuntu-latest
    concurrency:
      group: auto-update-pr-${{ github.event_name }}
      cancel-in-progress: true
    steps:
      - name: Update PRs that are behind main
        uses: actions/github-script@v9
        with:
          script: |
            const prNumber = context.payload.inputs?.pr_number;

            // Get list of open PRs
            const prs = prNumber
              ? [(await github.rest.pulls.get({
                  owner: context.repo.owner,
                  repo: context.repo.repo,
                  pull_number: parseInt(prNumber)
                })).data]
              : await github.paginate(github.rest.pulls.list, {
                  owner: context.repo.owner,
                  repo: context.repo.repo,
                  state: 'open',
                  sort: 'updated',
                  direction: 'desc'
                });

            console.log(`Found ${prs.length} open PRs to check`);

            // Constants for comment flood control
            const UPDATE_COMMENT_COOLDOWN_DAYS = 7;
            const COOLDOWN_MS = UPDATE_COMMENT_COOLDOWN_DAYS * 24 * 60 * 60 * 1000;

            for (const pr of prs) {
              // Skip bot PRs and drafts
              if (pr.user.login.includes('[bot]')) {
                console.log(`Skipping bot PR #${pr.number} from ${pr.user.login}`);
                continue;
              }
              if (pr.draft) {
                console.log(`Skipping draft PR #${pr.number}`);
                continue;
              }

              try {
                // Check if PR is behind main (base...head comparison)
                const { data: comparison } = await github.rest.repos.compareCommits({
                  owner: context.repo.owner,
                  repo: context.repo.repo,
                  base: pr.base.ref,  // main branch
                  head: `${pr.head.repo.owner.login}:${pr.head.ref}`  // Fully qualified ref for forks
                });

                if (comparison.behind_by > 0) {
                  console.log(`PR #${pr.number} is ${comparison.behind_by} commits behind ${pr.base.ref}`);

                  // Check if the PR allows maintainer edits
                  if (pr.maintainer_can_modify) {
                    // Try to update the branch
                    try {
                      await github.rest.pulls.updateBranch({
                        owner: context.repo.owner,
                        repo: context.repo.repo,
                        pull_number: pr.number
                      });

                      console.log(`✅ Updated PR #${pr.number}`);

                      // Add a comment
                      await github.rest.issues.createComment({
                        owner: context.repo.owner,
                        repo: context.repo.repo,
                        issue_number: pr.number,
                        body: `🔄 **Branch Updated**\n\nYour branch was ${comparison.behind_by} commits behind \`${pr.base.ref}\` and has been automatically updated. CI checks will re-run shortly.`
                      });
                    } catch (updateError) {
                      console.log(`Could not auto-update PR #${pr.number}: ${updateError.message}`);

                      // Determine the reason for failure
                      let failureReason = '';
                      if (updateError.status === 409 || updateError.message.includes('merge conflict')) {
                        failureReason = '\n\n**Note:** Automatic update failed due to merge conflicts. Please resolve them manually.';
                      } else if (updateError.status === 422) {
                        failureReason = '\n\n**Note:** Cannot push to fork. Please update manually.';
                      }

                      // Notify the contributor to update manually
                      await github.rest.issues.createComment({
                        owner: context.repo.owner,
                        repo: context.repo.repo,
                        issue_number: pr.number,
                        body: `⚠️ **Branch Update Required**\n\nYour branch is ${comparison.behind_by} commits behind \`${pr.base.ref}\`.${failureReason}\n\nPlease update your branch:\n\n\`\`\`bash\ngit fetch origin ${pr.base.ref}\ngit merge origin/${pr.base.ref}\ngit push\n\`\`\`\n\nOr use GitHub's "Update branch" button if available.`
                      });
                    }
                  } else {
                    // Can't modify, just notify
                    console.log(`PR #${pr.number} doesn't allow maintainer edits`);

                    // Check if we already commented recently (within last 7 days)
                    const { data: comments } = await github.rest.issues.listComments({
                      owner: context.repo.owner,
                      repo: context.repo.repo,
                      issue_number: pr.number,
                      since: new Date(Date.now() - COOLDOWN_MS).toISOString()
                    });

                    const hasRecentUpdateComment = comments.some(c =>
                      c.body?.includes('Branch Update Required') &&
                      c.user?.login === 'github-actions[bot]'
                    );

                    if (!hasRecentUpdateComment) {
                      await github.rest.issues.createComment({
                        owner: context.repo.owner,
                        repo: context.repo.repo,
                        issue_number: pr.number,
                        body: `⚠️ **Branch Update Required**\n\nYour branch is ${comparison.behind_by} commits behind \`${pr.base.ref}\`. Please update your branch to ensure CI checks run with the latest code:\n\n\`\`\`bash\ngit fetch origin ${pr.base.ref}\ngit merge origin/${pr.base.ref}\ngit push\n\`\`\`\n\nNote: Enable "Allow edits by maintainers" to allow automatic updates.`
                      });
                    }
                  }
                } else {
                  console.log(`PR #${pr.number} is up to date`);
                }
              } catch (error) {
                console.error(`Error processing PR #${pr.number}:`, error.message);
              }
            }

            // Log rate limit status
            const { data: rateLimit } = await github.rest.rateLimit.get();
            console.log(`API rate limit remaining: ${rateLimit.rate.remaining}/${rateLimit.rate.limit}`);