Add an init script of precommit hook with scalafmt. (#177)

* Add an init script of precommit hook with scalafmt.
* Readme update about scalafmt.

README.md

@@ -4,7 +4,7 @@
 
 ## Development
 
-To work on the Scala API, run sbt using `sbt -DdevMode` (the devMode
+To work on the Scala API, run sbt using `sbt -DdevMode=true` (the devMode
 option allows to skip webpack execution to speed up execution). You can
 use `~compile` or `~test` on the root project or focus on a specific
 project using `~timeseries/test`.
@@ -33,15 +33,23 @@ Use `yarn format` to format the Javascript files.
 
 ### Scalafmt
 
-We use Scalafmt to enforce style.  The minimal config is found in the
+We use Scalafmt to enforce style. The minimal config is found in the
 .scalafmt.conf file (you probably won't make any friends if you change
 this).
 
-To use you can install the [IntelliJ
+Several ways to use it:
+
+1. We provide a `git-init-scalafmt-precommit-hook.sh` that **replaces you git precommit hook** by a Scalafmt check.
+
+__Note__:
+  - It works only in UNIX like systems with bash installed.
+  - [You need a Scalafmt installed in your PATH in CLI mode](http://scalameta.org/scalafmt/#CLI).
+
+2. You can install the [IntelliJ
 plugin](http://scalameta.org/scalafmt/#IntelliJ) and use the familiar
 shift-ctrl-L shortcut.
 
-You can also use the sbt plugin:
+3. You can also use the sbt plugin:
 ```
 $> sbt "scalafmt -i"
 ```

git-init-scalafmt-precommit-hook.sh

@@ -0,0 +1,18 @@
+#!/usr/bin/env bash
+# This script creates a pre-commit git hook that run scalafmt before each commit
+# http://scalameta.org/scalafmt/
+# Need scalafmt installed in CLI mode.
+# Tested in Ubuntu's bash.
+[ -d .git/hooks/ ] || (echo "It's not a git directory";exit 1)
+[ -d .git/hooks/ ] && echo '#!/usr/bin/env bash
+echo -e "\e[0;33m Scalafmt RUNNING \e[0m"
+scalafmt --git true --diff-branch $(git branch | grep \* | cut -d " " -f2)
+RESULT=$?
+if [ ${RESULT} -ne 0 ]; then
+    echo -e "\e[0;31m Scalafmt FAILED \e[0m"
+    exit ${RESULT}
+fi
+echo -e "\e[0;32m Scalafmt SUCCEEDED \e[0m"
+exit 0
+' > .git/hooks/pre-commit
+chmod +x .git/hooks/pre-commit