name: Loadgen image

# Builds and publishes the relay load generator image as
# ghcr.io/block/buzz-loadgen (see Dockerfile.loadgen and perf/LOADGEN.md).
#
# Strategy mirrors sprig-image.yml: each architecture builds on its native
# runner, pushes to GHCR by digest, then a merge job stitches the per-arch
# digests into one multi-arch manifest and attests provenance.
#
# Triggers:
#   - push to main (paths-filtered) → :main + :sha-<7>
#   - pull_request (paths-filtered) → build only, no image push (same-repo
#     PRs still write the registry build cache, as in sprig-image.yml)
#   - workflow_dispatch             → manual publish at the current ref
#
# NOTE: the first push creates the GHCR package PRIVATE by default. An org
# admin must flip ghcr.io/block/buzz-loadgen to public once (Package settings →
# Change visibility). Subsequent pushes keep the visibility.

on:
  push:
    branches: [main]
    paths:
      - "Dockerfile.loadgen"
      - ".github/workflows/loadgen-image.yml"
      - ".cargo/config.toml"
      - "Cargo.toml"
      - "Cargo.lock"
      - "rust-toolchain.toml"
      - "crates/buzz-test-client/**"
      - "crates/buzz-ws-client/**"
      - "crates/buzz-core/**"
  pull_request:
    paths:
      - "Dockerfile.loadgen"
      - ".github/workflows/loadgen-image.yml"
  workflow_dispatch: {}

concurrency:
  group: loadgen-image-${{ github.ref }}
  cancel-in-progress: ${{ github.event_name == 'pull_request' }}

permissions: {}

env:
  IMAGE_NAME: ghcr.io/block/buzz-loadgen

jobs:
  build:
    name: Build (${{ matrix.platform }})
    runs-on: ${{ matrix.runner }}
    timeout-minutes: 60
    permissions:
      contents: read
      packages: write
      id-token: write
      attestations: write
    strategy:
      fail-fast: false
      matrix:
        include:
          - platform: linux/amd64
            runner: ubuntu-24.04
            arch: amd64
          - platform: linux/arm64
            runner: ubuntu-24.04-arm
            arch: arm64

    steps:
      - name: Checkout
        uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10  # v6.0.3
        with:
          persist-credentials: false

      - name: Set up Docker Buildx
        uses: docker/setup-buildx-action@d7f5e7f509e45cec5c76c4d5afdd7de93d0b3df5  # v4.1.0
        with:
          # Same OOM cap as docker.yml and sprig-image.yml.
          buildkitd-config-inline: |
            [worker.oci]
              max-parallelism = 2

      - name: Log in to GHCR
        if: github.event_name != 'pull_request' || github.event.pull_request.head.repo.full_name == github.repository
        uses: docker/login-action@650006c6eb7dba73a995cc03b0b2d7f5ca915bee  # v4.2.0
        with:
          registry: ghcr.io
          username: ${{ github.repository_owner }}
          password: ${{ secrets.GITHUB_TOKEN }}

      - name: Extract metadata
        id: meta
        uses: docker/metadata-action@80c7e94dd9b9319bd5eb7a0e0fe9291e23a2a2e9  # v6.1.0
        with:
          images: ${{ env.IMAGE_NAME }}
          flavor: |
            latest=false
          tags: |
            type=ref,event=branch
            type=sha,prefix=sha-,format=short
          labels: |
            org.opencontainers.image.title=Buzz Loadgen
            org.opencontainers.image.description=Scenario-driven Buzz relay load generator
            org.opencontainers.image.licenses=Apache-2.0

      - name: Build and push by digest
        id: build
        uses: docker/build-push-action@f9f3042f7e2789586610d6e8b85c8f03e5195baf  # v7.2.0
        with:
          context: .
          file: ./Dockerfile.loadgen
          platforms: ${{ matrix.platform }}
          labels: ${{ steps.meta.outputs.labels }}
          outputs: type=image,name=${{ env.IMAGE_NAME }},push-by-digest=true,name-canonical=true,push=${{ github.event_name != 'pull_request' }}
          cache-from: |
            type=registry,ref=${{ env.IMAGE_NAME }}-buildcache:${{ matrix.arch }}
          cache-to: |
            ${{ (github.event_name != 'pull_request' || github.event.pull_request.head.repo.full_name == github.repository) && format('type=registry,ref={0}-buildcache:{1},mode=max,compression=zstd', env.IMAGE_NAME, matrix.arch) || '' }}

      - name: Export digest
        if: github.event_name != 'pull_request'
        env:
          DIGEST: ${{ steps.build.outputs.digest }}
        run: |
          mkdir -p /tmp/digests
          touch "/tmp/digests/${DIGEST#sha256:}"

      - name: Upload digest
        if: github.event_name != 'pull_request'
        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a  # v7.0.1
        with:
          name: loadgen-digest-${{ matrix.arch }}
          path: /tmp/digests/*
          if-no-files-found: error
          retention-days: 1

  merge:
    name: Merge multi-arch manifest
    if: github.event_name != 'pull_request'
    runs-on: ubuntu-24.04
    needs: build
    timeout-minutes: 15
    permissions:
      contents: read
      packages: write
      id-token: write
      attestations: write

    steps:
      - name: Download per-arch digests
        uses: actions/download-artifact@3e5f45b2cfb9172054b4087a40e8e0b5a5461e7c  # v8.0.1
        with:
          path: /tmp/digests
          pattern: loadgen-digest-*
          merge-multiple: true

      - name: Set up Docker Buildx
        uses: docker/setup-buildx-action@d7f5e7f509e45cec5c76c4d5afdd7de93d0b3df5  # v4.1.0

      - name: Log in to GHCR
        uses: docker/login-action@650006c6eb7dba73a995cc03b0b2d7f5ca915bee  # v4.2.0
        with:
          registry: ghcr.io
          username: ${{ github.repository_owner }}
          password: ${{ secrets.GITHUB_TOKEN }}

      - name: Extract metadata
        id: meta
        uses: docker/metadata-action@80c7e94dd9b9319bd5eb7a0e0fe9291e23a2a2e9  # v6.1.0
        with:
          images: ${{ env.IMAGE_NAME }}
          # Must mirror the build job's tag matrix exactly.
          flavor: |
            latest=false
          tags: |
            type=ref,event=branch
            type=sha,prefix=sha-,format=short

      - name: Create and push manifest list
        id: manifest
        working-directory: /tmp/digests
        env:
          IMAGE_NAME: ${{ env.IMAGE_NAME }}
          META_TAGS: ${{ steps.meta.outputs.tags }}
        run: |
          set -euo pipefail
          tags=()
          while IFS= read -r tag; do
            [ -n "$tag" ] && tags+=("-t" "$tag")
          done <<< "$META_TAGS"

          digests=()
          for digest in *; do
            digests+=("${IMAGE_NAME}@sha256:${digest}")
          done

          docker buildx imagetools create "${tags[@]}" "${digests[@]}"

          first_tag=$(echo "$META_TAGS" | head -n1)
          merged_digest=$(docker buildx imagetools inspect "$first_tag" \
            --format '{{json .Manifest}}' | jq -r '.digest')
          echo "digest=${merged_digest}" >> "$GITHUB_OUTPUT"

      - name: Attest provenance for the merged image
        # Verify with: gh attestation verify oci://ghcr.io/block/buzz-loadgen:<tag> --owner block
        uses: actions/attest-build-provenance@0f67c3f4856b2e3261c31976d6725780e5e4c373  # v4.1.1
        with:
          subject-name: ${{ env.IMAGE_NAME }}
          subject-digest: ${{ steps.manifest.outputs.digest }}
          push-to-registry: true

      - name: Summary
        env:
          IMAGE_NAME: ${{ env.IMAGE_NAME }}
          DIGEST: ${{ steps.manifest.outputs.digest }}
        run: |
          {
            echo "### Loadgen image published"
            echo '```'
            echo "${IMAGE_NAME}@${DIGEST}"
            echo '```'
          } >> "$GITHUB_STEP_SUMMARY"