name: Benchmark PR Comparison
on:
  pull_request:
    branches: [main]
    paths:
      - 'src/**'
      - 'tests/benchmarks/**'
      - 'package.json'
      - 'vitest.config.benchmark.ts'

permissions:
  pull-requests: write
  contents: read

jobs:
  benchmark-comparison:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout PR branch
        uses: actions/checkout@v4
        with:
          fetch-depth: 0
      
      - name: Setup Node.js
        uses: actions/setup-node@v4
        with:
          node-version: 20
          cache: 'npm'
      
      - name: Install dependencies
        run: npm ci
      
      # Run benchmarks on current branch
      - name: Run current benchmarks
        run: npm run benchmark:ci
      
      - name: Save current results
        run: cp benchmark-results.json benchmark-current.json
      
      # Checkout and run benchmarks on base branch
      - name: Checkout base branch
        run: |
          git checkout ${{ github.event.pull_request.base.sha }}
          git status
      
      - name: Install base dependencies
        run: npm ci
      
      - name: Run baseline benchmarks
        run: npm run benchmark:ci
        continue-on-error: true
      
      - name: Save baseline results
        run: |
          if [ -f benchmark-results.json ]; then
            cp benchmark-results.json benchmark-baseline.json
          else
            echo '{"files":[]}' > benchmark-baseline.json
          fi
      
      # Compare results
      - name: Checkout PR branch again
        run: git checkout ${{ github.event.pull_request.head.sha }}
      
      - name: Compare benchmarks
        id: compare
        run: |
          node scripts/compare-benchmarks.js benchmark-current.json benchmark-baseline.json || echo "REGRESSION=true" >> $GITHUB_OUTPUT
      
      # Upload comparison artifacts
      - name: Upload benchmark comparison
        if: always()
        uses: actions/upload-artifact@v4
        with:
          name: benchmark-comparison-${{ github.run_number }}
          path: |
            benchmark-current.json
            benchmark-baseline.json
            benchmark-comparison.json
            benchmark-comparison.md
          retention-days: 30
      
      # Post comparison to PR
      - name: Post benchmark comparison to PR
        if: always()
        uses: actions/github-script@v7
        with:
          script: |
            const fs = require('fs');
            let comment = '## ⚡ Benchmark Comparison\n\n';
            
            try {
              if (fs.existsSync('benchmark-comparison.md')) {
                const comparison = fs.readFileSync('benchmark-comparison.md', 'utf8');
                comment += comparison;
              } else {
                comment += 'Benchmark comparison could not be generated.';
              }
            } catch (error) {
              comment += `Error reading benchmark comparison: ${error.message}`;
            }
            
            comment += '\n\n---\n';
            comment += `*[View full benchmark results](https://github.com/${{ github.repository }}/actions/runs/${{ github.run_id }})*`;
            
            // Find existing comment
            const { data: comments } = await github.rest.issues.listComments({
              owner: context.repo.owner,
              repo: context.repo.repo,
              issue_number: context.issue.number,
            });
            
            const botComment = comments.find(comment => 
              comment.user.type === 'Bot' && 
              comment.body.includes('## ⚡ Benchmark Comparison')
            );
            
            if (botComment) {
              await github.rest.issues.updateComment({
                owner: context.repo.owner,
                repo: context.repo.repo,
                comment_id: botComment.id,
                body: comment
              });
            } else {
              await github.rest.issues.createComment({
                owner: context.repo.owner,
                repo: context.repo.repo,
                issue_number: context.issue.number,
                body: comment
              });
            }
      
      # Add status check
      - name: Set benchmark status
        if: always()
        uses: actions/github-script@v7
        with:
          script: |
            const hasRegression = '${{ steps.compare.outputs.REGRESSION }}' === 'true';
            const state = hasRegression ? 'failure' : 'success';
            const description = hasRegression 
              ? 'Performance regressions detected' 
              : 'No performance regressions';
            
            await github.rest.repos.createCommitStatus({
              owner: context.repo.owner,
              repo: context.repo.repo,
              sha: context.sha,
              state: state,
              target_url: `https://github.com/${{ github.repository }}/actions/runs/${{ github.run_id }}`,
              description: description,
              context: 'benchmarks/regression-check'
            });