.github/workflows/performance-pr.yml

name: Performance Comparison for Pull Requests

on:
  pull_request:
    branches: [master]

permissions:
  contents: read
  pull-requests: write

jobs:
  benchmark-pr:
    name: Performance benchmark comparison
    runs-on: ubuntu-latest
    steps:
      - name: Checkout PR branch
        uses: actions/checkout@v4
        with:
          ref: ${{ github.event.pull_request.head.sha }}

      - name: Set up Go
        uses: actions/setup-go@v5
        with:
          go-version: '1.21'

      # Save commit SHAs for display
      - name: Save commit info
        id: commits
        run: |
          BASE_SHA="${{ github.event.pull_request.base.sha }}"
          HEAD_SHA="${{ github.event.pull_request.head.sha }}"
          echo "base_short=${BASE_SHA:0:7}" >> $GITHUB_OUTPUT
          echo "head_short=${HEAD_SHA:0:7}" >> $GITHUB_OUTPUT

      # Run benchmark on PR branch
      - name: Run benchmark on PR branch
        run: |
          go test -bench '.' -benchtime=2s -benchmem ./... | tee pr-bench.txt

      # Checkout base branch and run benchmark
      - name: Checkout base branch
        uses: actions/checkout@v4
        with:
          ref: ${{ github.event.pull_request.base.sha }}
          clean: false
          path: base

      - name: Run benchmark on base branch
        working-directory: base
        run: |
          go test -bench '.' -benchtime=2s -benchmem ./... | \
            tee ../base-bench.txt

      # Install benchstat for comparison
      - name: Install benchstat
        run: go install golang.org/x/perf/cmd/benchstat@latest

      # Compare benchmarks using benchstat
      - name: Compare benchmarks with benchstat
        id: benchstat
        run: |
          cat > comparison.md << 'EOF'
          ## Benchmark Comparison

          Comparing base branch (`${{ steps.commits.outputs.base_short }}`)
          vs PR branch (`${{ steps.commits.outputs.head_short }}`)

          ```
          EOF
          benchstat base-bench.txt pr-bench.txt >> comparison.md || true
          echo '```' >> comparison.md
        continue-on-error: true

      # Post comment with results
      - name: Post benchmark comparison comment
        uses: actions/github-script@v7
        with:
          script: |
            const fs = require('fs');
            const comparison = fs.readFileSync('comparison.md', 'utf8');

            // 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')
            );

            const footer = '<sub>🤖 This comment will be ' +
              'automatically updated with the latest benchmark results.</sub>';
            const commentBody = `${comparison}\n\n${footer}`;

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