feat(kubectl): publish diff if on github ci as PR comment

Author: blaggacao

src/std/fwlib/blockTypes/kubectl.nix

@@ -123,9 +123,6 @@ in
         ${build}
         build
 
-        KUBECTL_EXTERNAL_DIFF="icdiff -N -r"
-        export KUBECTL_EXTERNAL_DIFF
-
         diff() {
           kubectl diff ${
           if usesKustomize
@@ -134,7 +131,34 @@ in
         } "$manifest_path";
         }
 
-        diff
+        # GitHub case
+        if [[ -v CI ]] && [[ -v BRANCH ]] && [[ -v OWNER_AND_REPO ]] && command gh > /dev/null ; then
+
+          set +e # diff exits 1 if diff existed
+          read -r -d "" DIFFSTREAM <<DIFF
+        ## Standard DiffPost
+
+        This PR would generate the following \`kubectl\` diff:
+
+        <details><summary>Preview</summary>
+
+        \`\`\`diff
+        $(diff)
+        \`\`\`
+
+        </details>
+        DIFF
+          set -e # we're past the invocation of diff
+
+          if ! gh pr --repo "$OWNER_AND_REPO" comment "$BRANCH" --edit-last -b "$DIFFSTREAM"; then
+            echo "Make a first post ..."
+            gh pr --repo "$OWNER_AND_REPO" comment "$BRANCH" -b "$DIFFSTREAM"
+          fi
+        else
+          KUBECTL_EXTERNAL_DIFF="icdiff -N -r"
+          export KUBECTL_EXTERNAL_DIFF
+          diff
+        fi
       '' {})
       (mkCommand currentSystem "apply" "Apply the manifests to K8s" [pkgs.kubectl pkgs.icdiff] ''
         ${build}