name: Build containers when image tags change

on:
  push:
    # Uncomment/adjust once working:
    # branches: [ master ]
    paths:
      - "helm/shorefront/values.yaml"
      - "frontend/Dockerfile"
      - "backend/Dockerfile"
      - ".gitea/workflows/build-containers-on-demand.yml"

jobs:
  build-if-image-changed:
    runs-on: ubuntu-latest
    strategy:
      fail-fast: false
      matrix:
        include:
          - container_name: shorefront-frontend
            image_yq_path: .frontend.image
            expected_repo: git.baumann.gr/adebaumann/shorefront-frontend
            dockerfile: frontend/Dockerfile
            build_context: frontend
            description: shorefront frontend
          - container_name: shorefront-backend
            image_yq_path: .backend.image
            expected_repo: git.baumann.gr/adebaumann/shorefront-backend
            dockerfile: backend/Dockerfile
            build_context: backend
            description: shorefront backend

    env:
      DEPLOY_FILE: "helm/shorefront/values.yaml"
      CONTAINER_NAME: ${{ matrix.container_name }}
      EXPECTED_REPO: ${{ matrix.expected_repo }}

    steps:
      - name: Checkout
        uses: actions/checkout@v4
        with:
          fetch-depth: 2

      - name: Determine base commit
        id: base
        shell: bash
        run: |
          set -euo pipefail
          if git rev-parse --verify -q HEAD~1 >/dev/null; then
            echo "base=$(git rev-parse HEAD~1)" >> "$GITHUB_OUTPUT"
          else
            echo "base=$(git hash-object -t tree /dev/null)" >> "$GITHUB_OUTPUT"
          fi

      - name: Install yq
        shell: bash
        run: |
          set -euo pipefail
          YQ_VER=v4.44.3
          curl -sL "https://github.com/mikefarah/yq/releases/download/${YQ_VER}/yq_linux_amd64" -o /usr/local/bin/yq
          chmod +x /usr/local/bin/yq
          yq --version

      - name: Read ${{ matrix.description }} image from Helm values
        id: img
        shell: bash
        run: |
          set -euo pipefail
          file="${DEPLOY_FILE}"
          expected_repo="${EXPECTED_REPO}"

          echo "========================================"
          echo "Reading image from: $file"
          echo "Expected repo: $expected_repo"
          echo "========================================"

          new_repo=$(yq -r '${{ matrix.image_yq_path }}' "$file")
          new_tag=$(yq -r '.containers.version' "$file")
          new_image="${new_repo}:${new_tag}"

          if git cat-file -e "${{ steps.base.outputs.base }}:$file" 2>/dev/null; then
            old_repo=$(git show "${{ steps.base.outputs.base }}:$file" | yq -r '${{ matrix.image_yq_path }}' || true)
            old_tag=$(git show "${{ steps.base.outputs.base }}:$file" | yq -r '.containers.version' || true)
            old_image="${old_repo}:${old_tag}"
          else
            old_image="<none>"
          fi

          echo "Old image: ${old_image}"
          echo "New image: ${new_image}"

          if [ -z "${new_repo:-}" ] || [ "$new_repo" = "null" ]; then
            echo "ERROR: Could not read ${{ matrix.image_yq_path }} from $file"
            exit 1
          fi

          if [[ "$new_repo" != "$expected_repo" ]]; then
            echo "ERROR: Found image repo \"$new_repo\" but expected \"$expected_repo\""
            exit 1
          fi

          registry="$(echo "$new_repo" | awk -F/ '{print $1}')"

          {
            echo "new_image=$new_image"
            echo "new_repo=$new_repo"
            echo "new_tag=$new_tag"
            echo "registry=$registry"
          } >> "$GITHUB_OUTPUT"

      - name: Check if image exists on registry
        id: check_image
        shell: bash
        run: |
          set -euo pipefail
          new_repo="${{ steps.img.outputs.new_repo }}"
          new_tag="${{ steps.img.outputs.new_tag }}"
          registry_user="${{ gitea.actor }}"
          registry_password="${{ secrets.REGISTRY_TOKEN }}"

          registry_host=$(echo "$new_repo" | cut -d/ -f1)
          image_path=$(echo "$new_repo" | cut -d/ -f2-)

          echo "Checking if $new_repo:$new_tag exists on registry $registry_host"

          manifest_url="https://${registry_host}/v2/${image_path}/manifests/${new_tag}"

          http_code=$(curl -s -o /dev/null -w "%{http_code}" \
            -u "${registry_user}:${registry_password}" \
            -H "Accept: application/vnd.docker.distribution.manifest.v2+json,application/vnd.docker.distribution.manifest.list.v2+json" \
            "$manifest_url" || echo "000")

          if [ "$http_code" = "200" ]; then
            echo "Image already exists on registry (HTTP $http_code)"
            echo "exists=true" >> "$GITHUB_OUTPUT"
          else
            echo "Image does not exist on registry (HTTP $http_code)"
            echo "exists=false" >> "$GITHUB_OUTPUT"
          fi

      - name: Skip if image already exists
        if: steps.check_image.outputs.exists == 'true'
        run: echo "${{ matrix.description }} image ${{ steps.img.outputs.new_image }} already exists on registry; skipping build."

      - name: Set up Buildx
        if: steps.check_image.outputs.exists == 'false'
        uses: docker/setup-buildx-action@v3

      - name: Log in to registry
        if: steps.check_image.outputs.exists == 'false'
        uses: docker/login-action@v3
        with:
          registry: ${{ steps.img.outputs.registry }}
          username: ${{ gitea.actor }}
          password: ${{ secrets.REGISTRY_TOKEN }}

      - name: Build and push ${{ matrix.description }} (exact tag from Helm values)
        if: steps.check_image.outputs.exists == 'false'
        uses: docker/build-push-action@v6
        with:
          context: ${{ matrix.build_context }}
          file: ${{ matrix.dockerfile }}
          push: true
          tags: |
            ${{ steps.img.outputs.new_image }}
            ${{ steps.img.outputs.new_repo }}:latest
          labels: |
            org.opencontainers.image.source=${{ gitea.repository }}
            org.opencontainers.image.revision=${{ gitea.sha }}
          cache-from: type=gha
          cache-to: type=gha,mode=max