ci: build-oci-image: cache .git dir in build-oci-image

ci: build-oci-image: fix logic for detecting changes to .docker in build-oci-image

ci: build-oci-image: use registry url variable, not hardcoded url

ci: build-oci-image: change changes_detected var to build image

ci: build-oci-image: output an image tag for other jobs to use

ci: build-oci-image: cache the docker image build

This wont always speed things up, but occasionally it will speed things
up by a lot

.gitea/workflows/gentoo-utils.yml

@@ -11,6 +11,12 @@ jobs:
     runs-on: ubuntu-latest
     continue-on-error: true
     steps:
+      - name: Restore git cache
+        uses: actions/cache@v4
+        with:
+          path: .git
+          key: gitea-repo-${{ gitea.repository }}-${{ gitea.ref }}
+
       - name: Checkout repo
         uses: actions/checkout@v5
         with:
@@ -18,33 +24,65 @@ jobs:
 
       - name: Check for changes before building
         id: image-changes
+        # build image only if 1. changes are detected or 2. an image for the working branch doesnt exist
         run: |
-          echo "branch_name=${GITHUB_HEAD_REF:-${GITHUB_REF#refs/heads/}}" >> $GITEA_OUTPUT
+          branch_name="${GITHUB_HEAD_REF:-${GITHUB_REF#refs/heads/}}"
-          if ! git diff ${{ gitea.event.before }} ${{ gitea.sha }} --no-patch --exit-code .docker; then
+          default_branch_name="${{ gitea.event.repository.default_branch }}"
-            echo changes_detected=true >> $GITEA_OUTPUT
+          image_tag=latest
-          else
+          comparison_hash="${{ gitea.event.before }}"
-            echo changes_detected=false >> $GITEA_OUTPUT
+
+          if [[ "$branch_name" != "$default_branch_name" ]]; then
+            image_tag=$branch_name
           fi
+          # slugify
+          image_tag="$(echo "$image_tag" | sed -E 's/[^a-zA-Z0-9]/-/g')"
+
+          # rebase breaks gitea.event.before, so check to make sure the hash provided exists
+          if ! git merge-base --is-ancestor $comparison_hash $branch_name >/dev/null 2>&1; then
+            comparison_hash=$(git merge-base origin/$default_branch_name $branch_name)
+          fi
+            
+          if ! git diff $comparison_hash ${{ gitea.sha }} --no-patch --exit-code .docker; then
+            build_image=true
+          else
+            if ! docker manifest inspect ${{ vars.REGISTRY_URL }}/${{ gitea.repository }}:${image_tag} >/dev/null 2>&1; then
+              build_image=true
+            else
+              build_image=false
+            fi
+          fi
+
+          echo "default_branch_name=$default_branch_name" >> $GITEA_OUTPUT
+          echo "branch_name=$branch_name" >> $GITEA_OUTPUT
+          echo "image_tag=$image_tag" >> $GITEA_OUTPUT
+          echo "comparison_hash=$comparison_hash" >> $GITEA_OUTPUT
+          echo "build_image=$build_image" >> $GITEA_OUTPUT
           cat $GITEA_OUTPUT
       - name: Set up Docker buildx
-        if: steps.image-changes.outputs.changes_detected == 'true'
+        if: steps.image-changes.outputs.build_image == 'true'
         uses: docker/setup-buildx-action@v3
+        with:
+          driver-opts: network=runners-net
 
       - name: Log in to Github Container Registry
-        if: steps.image-changes.outputs.changes_detected == 'true'
+        if: steps.image-changes.outputs.build_image == 'true'
         uses: docker/login-action@v3
         with:
-          registry: git.epenguin.net
+          registry: ${{ vars.REGISTRY_URL }}
           username: ${{ vars.CI_BOT_USERNAME }}
           password: ${{ secrets.CI_BOT_TOKEN }}
 
       - name: Build and push
-        if: steps.image-changes.outputs.changes_detected == 'true'
+        if: steps.image-changes.outputs.build_image == 'true'
         uses: docker/build-push-action@v6
         with:
           push: true
-          tags: git.epenguin.net/${{ gitea.repository }}:latest
+          tags: ${{ vars.REGISTRY_URL }}/${{ gitea.repository }}:${{ steps.image-changes.outputs.image_tag }}
           context: "{{defaultContext}}:.docker"
+          cache-from: type=gha
+          cache-to: type=gha,mode=max
+    outputs:
+      image_tag: ${{ steps.image-changes.outputs.image_tag }}
 
   build:
     runs-on: brutalisk