Resolve "add MR preview"

Closes #41 (closed)

.gitlab-ci.yml

 image: node:14.17.1-slim
 
 stages:
-  - test
-  - build
+  - 🧪 test
+  - 📝 publish
+  - 🧽 clean
+
+variables:
+  SUB_GROUP:          "www"
+  DOCUSAURUS_BASEURL: /
+
 
 lint:
-  stage: test
+  stage: 🧪 test
   tags:
     - cache
   script: 
@@ -19,7 +25,7 @@ lint:
       - node_modules
 
 pages:
-  stage: build
+  stage: 📝 publish
   tags:
     - cache
   script:
@@ -34,5 +40,36 @@ pages:
         - package.json
     paths:
       - node_modules
-  only:
-    - master
+  rules:
+    - if: $CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH
+  environment:
+    name: production
+    url: "${DOCUSAURUS_URL}"
+
+pages:preview:
+  extends: pages
+  artifacts:
+    expire_in: 2 week
+  rules:
+    - if: $CI_MERGE_REQUEST_IID
+      variables:
+          DOCUSAURUS_URL:     "https://${CI_PROJECT_ROOT_NAMESPACE}.${CI_PAGES_DOMAIN}"
+          DOCUSAURUS_BASEURL: "/-/${SUB_GROUP}/${CI_PROJECT_NAME}/-/jobs/${CI_JOB_ID}/artifacts/public/"
+
+  environment:
+    name: preview/${CI_COMMIT_REF_NAME}
+    url: "https://${CI_PROJECT_ROOT_NAMESPACE}.${CI_PAGES_DOMAIN}/-/${SUB_GROUP}/${CI_PROJECT_NAME}/-/jobs/${CI_JOB_ID}/artifacts/public/index.html"
+    on_stop: pages:preview:stop
+
+pages:preview:stop:
+  stage: 🧽 clean
+  rules:
+    - if: $CI_MERGE_REQUEST_IID
+      when: manual
+  allow_failure: true
+  environment:
+    name: preview/${CI_COMMIT_REF_NAME}
+    action: stop
+  script:
+    - echo "🧽 clean MR environment [preview/${CI_COMMIT_REF_NAME}]"
+