name: Build image when workload image tag changes

on:
  push:
    branches: [ deployment ]                 # adjust if needed
    paths:
      - "arcocd/deployment.yaml"
      - "Dockerfile"                   # keep if you also want to rebuild when Dockerfile changes

jobs:
  build-if-image-changed:
    runs-on: ubuntu-latest

    env:
      DEPLOY_FILE: "arcocd/deployment.yaml"
      TARGET_REPO: "git.baumann.gr/adebaumann/vui"   # repo (no tag)

    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

      # Install yq for robust YAML parsing
      - 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 workload image from deployment (old vs new)
        id: img
        shell: bash
        run: |
          set -euo pipefail
          file="$DEPLOY_FILE"
          repo="$TARGET_REPO"

          # Function: from a deployment yaml, read .spec.template.spec.containers[].image
          # and select the one whose image starts with "$repo:"
          extract() {
            yq -r '
              .spec.template.spec.containers // []                       # only real containers, not initContainers
              | map(.image) | .[]?                                        # images as strings
              | select(startswith(env(repo) + ":"))                       # match exact repo + ":"
            ' "$1" 2>/dev/null | tail -n 1
          }

          # Old image from previous commit (if file existed)
          if git cat-file -e "${{ steps.base.outputs.base }}":"$file" 2>/dev/null; then
            git show "${{ steps.base.outputs.base }}:$file" > /tmp/old.yaml
            old_image="$(extract /tmp/old.yaml || true)"
          else
            old_image=""
          fi

          # New image from workspace
          if [ -f "$file" ]; then
            new_image="$(extract "$file" || true)"
          else
            new_image=""
          fi

          echo "Old workload image: $old_image"
          echo "New workload image: $new_image"

          # Helpers to split repo and tag (handles registry with port)
          parse_tag() {
            local ref="$1"
            local after_slash="${ref##*/}"
            if [[ "$after_slash" == *:* ]]; then echo "${after_slash##*:}"; else echo ""; fi
          }
          parse_repo() {
            local ref="$1"
            local tag="$(parse_tag "$ref")"
            if [ -n "$tag" ]; then echo "${ref%:$tag}"; else echo "$ref"; fi
          }

          old_tag="$(parse_tag "$old_image")"
          new_tag="$(parse_tag "$new_image")"
          new_repo="$(parse_repo "$new_image")"

          if [ -z "$new_image" ]; then
            echo "ERROR: Could not find a containers[].image starting with ${repo}: in $file"
            exit 1
          fi

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

          {
            echo "changed=$([ "$old_tag" != "$new_tag" ] && echo true || echo false)"
            echo "new_image=$new_image"
            echo "new_repo=$new_repo"
            echo "new_tag=$new_tag"
            echo "registry=$registry"
          } >> "$GITHUB_OUTPUT"

      - name: Skip if tag unchanged
        if: steps.img.outputs.changed != 'true'
        run: echo "Workload image tag unchanged in ${{ env.DEPLOY_FILE }}; skipping build."

      - name: Set up Buildx
        if: steps.img.outputs.changed == 'true'
        uses: docker/setup-buildx-action@v3

      - name: Log in to registry
        if: steps.img.outputs.changed == 'true'
        uses: docker/login-action@v3
        with:
          registry: ${{ steps.img.outputs.registry }}
          username: ${{ secrets.REGISTRY_USER }}
          password: ${{ secrets.REGISTRY_PASSWORD }}

      - name: Build and push (exact tag from deployment)
        if: steps.img.outputs.changed == 'true'
        uses: docker/build-push-action@v6
        with:
          context: .
          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