Implement automatic build when upstream updates

Also tagging 1.xx versions now in addition to `latest`

.forgejo/workflows/build.yaml

@@ -1,27 +1,54 @@
-on: [push]
+on:
+  push:
+  schedule:
+    - cron:  '0 * * * *'
 jobs:
+  name: Build image
   build_image:
+    env:
+      VERSION: 1.21
+      SCHEDULED: ${{ github.event_name == 'schedule' }}
+      PUSHED: ${{ github.event_name == 'push' }} 
+      REGISTRY: git.korhonen.cc
+      REPO: ${{ env.REGISTRY }}/functionalhacker/forgejo-asciidoc
     runs-on: docker
     steps:
+      - name: Check if update available
+        if: env.SCHEDULED
+        id: check
+        uses: https://github.com/lucacome/docker-image-update-checker@v1
+        with:
+          base-image: codeberg.org/forgejo/forgejo:${{ env.FORGEJO_VERSION }}
+          image: ${{ env.REPO }}:latest
+      - name: Check result
+        if: env.SCHEDULED
+        run: echo "Needs updating = ${{ steps.check.outputs.needs-updating }}"
       - name: Set up Docker Buildx
+        if: env.PUSHED || ${{ steps.check.outputs.needs-updating == 'true' }}
         uses: docker/setup-buildx-action@v3
-      - name: Login to Docker registry (Forgejo)
+      - name: Login to Docker registry
+        if: env.PUSHED || ${{ steps.check.outputs.needs-updating == 'true' }}
         uses: docker/login-action@v3
         with:
-          registry: git.korhonen.cc
+          registry: ${{ env.REGISTRY }}
           username: ${{ secrets.REGISTRY_USER }}
           password: ${{ secrets.REGISTRY_PASSWORD }}
       - name: Build and push image
+        if: env.PUSHED || ${{ steps.check.outputs.needs-updating == 'true' }}
         uses: docker/build-push-action@v5
         with:
           push: true
-          tags: git.korhonen.cc/functionalhacker/forgejo-asciidoc
+          build-args: FORGEJO_VERSION=${{ env.FORGEJO_VERSION }}
+          tags: |
+            ${{ env.REPO }}:latest
+            ${{ env.REPO }}:${{ env.FORGEJO_VERSION }}
       - name: Notify in Telegram channel
+        if: env.PUSHED || ${{ steps.check.outputs.needs-updating == 'true' }}
         uses: https://github.com/appleboy/telegram-action@master
         with:
           to: "-1001915202306"
           token: ${{ secrets.TELEGRAM_TOKEN }}
           message: |
-            Newest version of forgejo-asciidoc support has just been built. docker pull away!
+            Newest version (v${{ env.FORGEJO_VERSION }}) of forgejo-asciidoc support has just been built. docker pull away!
 
             See details: https://git.korhonen.cc/FunctionalHacker/-/packages/container/forgejo-asciidoc/latest

Dockerfile

@@ -1,2 +1,3 @@
-FROM codeberg.org/forgejo/forgejo:1.21
+ARG FORGEJO_VERSION
+FROM codeberg.org/forgejo/forgejo:${FORGEJO_VERSION}
 RUN apk --no-cache add asciidoctor ruby-rouge