chore,ci: reduce frequency of scheduled docker image builds

Reduce amount of disk space we are costing GitHub. Currently we have
350+ tagged releases each more than 3GB, amounting to more than 1TB of
storage. This should reduce out future usage in the long run

GitHub actions run will be cancelled for this commit on master branch as
it does not make any changes to the built docker image, and the docker
image was just rebuilt in the previous commit for other unrelated
reasons

Author: thunder-coding

.github/workflows/docker_image.yml

@@ -33,29 +33,52 @@ jobs:
     steps:
     - name: Clone repository
       uses: actions/checkout@v6
+
+    # Skip building the Docker image on scheduled runs if the last successful
+    # image build (the one tagged "latest") is less than IMAGE_MIN_INTERVAL_DAYS old.
+    - name: Optionally skip building image
+      if: github.event_name == 'schedule'
+      id: skip-build
+      env:
+        IMAGE_MIN_INTERVAL_DAYS: 30
+      run: |
+        LAST_TIMESTAMP=$(curl -H "Authorization: Bearer ${{ secrets.GITHUB_TOKEN }}" \
+         -H "Accept: application/vnd.github+json" \
+         "https://api.github.com/users/termux/packages/container/package-builder/versions" |
+          jq --raw-output 'map(select(.metadata.container.tags | contains(["latest"])))[0].created_at')
+        LAST_UNIX_TIME=$(date -d "$LAST_TIMESTAMP" +%s)
+        CURRENT_UNIX_TIME=$(date +%s)
+        if (( "$CURRENT_UNIX_TIME" - "$LAST_UNIX_TIME" < $IMAGE_MIN_INTERVAL_DAYS*24*60*60 )); then
+          echo "Skipping building Docker image: last successful build was done on $LAST_TIMESTAMP (< $IMAGE_MIN_INTERVAL_DAYS days)"
+          echo "skip-build=true" >> "$GITHUB_OUTPUT"
+        fi
+
     - name: Build
+      if: ${{ steps.skip-build.outputs.skip-build != 'true' }}
       run: |
         docker build --tag termux/package-builder:latest scripts/
         docker tag termux/package-builder:latest ghcr.io/termux/package-builder:latest
     - name: Build (CGCT)
+      if: ${{ steps.skip-build.outputs.skip-build != 'true' }}
       run: |
         docker build --tag termux/package-builder-cgct:latest --file scripts/Dockerfile.cgct scripts/
         docker tag termux/package-builder-cgct:latest ghcr.io/termux/package-builder-cgct:latest
     - name: Login to GHCR
-      if: github.ref == 'refs/heads/master' && github.event_name != 'pull_request' && github.repository == 'termux/termux-packages'
+      if: github.ref == 'refs/heads/master' && github.event_name != 'pull_request' && github.repository == 'termux/termux-packages' && steps.skip-build.outputs.skip-build != 'true'
+
       uses: docker/login-action@v3
       with:
         registry: ghcr.io
         username: ${{ github.actor }}
         password: ${{ secrets.GITHUB_TOKEN }}
     - name: Login to Docker Hub
-      if: github.ref == 'refs/heads/master' && github.event_name != 'pull_request' && github.repository == 'termux/termux-packages'
+      if: github.ref == 'refs/heads/master' && github.event_name != 'pull_request' && github.repository == 'termux/termux-packages' && steps.skip-build.outputs.skip-build != 'true'
       uses: docker/login-action@v3
       with:
         username: grimler
         password: ${{ secrets.DOCKER_TOKEN }}
     - name: Push
-      if: github.ref == 'refs/heads/master' && github.event_name != 'pull_request' && github.repository == 'termux/termux-packages'
+      if: github.ref == 'refs/heads/master' && github.event_name != 'pull_request' && github.repository == 'termux/termux-packages' && steps.skip-build.outputs.skip-build != 'true'
       run: |
         # ghcr.io seem to be unstable sometimes. It may suddenly drop connection
         # during docker push when some layers are already uploaded. The workaround