circle.yml: deploy docs when the master branch is updated

Note that the push requires a specific private key in the libratbag
circle CI organization, meaning that only the master branch of libratbag
will be allowed to push to the doc repo.

Note also that only the master branch will trigger the request:
- any PR will not trigger the request
- any push on the master branch of a personal repo will fail while
  attempting to write the docs, if the repo is setup to use circleCI too.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@gmail.com>

circle.yml

@@ -125,6 +125,38 @@ doc_build: &doc_build
     - *export_logs
     - store_artifacts:
         path: ~/libratbag/build/doc/html
+    - persist_to_workspace:
+        root: build
+        paths:
+          - doc/html/*
+
+docs_deploy: &docs_deploy
+  <<: *default_settings
+  steps:
+    - run:
+        name: Install prerequisites
+        command: dnf install -y git tree
+    - checkout
+    - attach_workspace:
+        at: build
+    - run:
+        name: Clone doc repository
+        command: |
+          cd ~
+          git clone ssh://git@github.com/${CIRCLE_PROJECT_REPONAME}/${CIRCLE_PROJECT_REPONAME}.github.io
+    - run:
+        name: Copy the doc, commit and push
+        command: |
+          set +e
+          cd ~/${CIRCLE_PROJECT_REPONAME}.github.io
+          \cp -r ~/${CIRCLE_PROJECT_REPONAME}/build/doc/html/* .
+          if ! git diff-index --quiet HEAD --; then
+            git config --global user.email "libratbag@librabtag.github.io"
+            git config --global user.name "The libratbag crew"
+            git add .
+            git commit -m "update docs from ${CIRCLE_SHA1}"
+            git push
+          fi
 
 version: 2
 jobs:
@@ -148,6 +180,10 @@ jobs:
     <<: *scan_build_run
     docker:
       - image: fedora:latest
+  doc_deploy:
+    <<: *docs_deploy
+    docker:
+      - image: fedora:latest
 
 
 workflows:
@@ -159,3 +195,9 @@ workflows:
       - ubuntu_17_04
       - fedora_latest
       - doc_build
+      - doc_deploy:
+          requires:
+            - doc_build
+          filters:
+              branches:
+                only: master