Automate version code generation.

app/build.gradle

@@ -36,6 +36,14 @@ String gitHash() {
     return githashP.text.trim()
 }
 
+Integer gitVersionCode() {
+    def gitP = 'git rev-list v2..HEAD --count'.execute()
+    gitP.waitFor()
+    if (gitP.exitValue())
+        throw new GradleException("Couldn't extract number of commit after v2.")
+    return gitP.text.trim().toInteger()
+}
+
 String buildDate() {
     def builddate = new Date()
     return builddate.toString()
@@ -53,8 +61,8 @@ android {
         applicationId "org.vostan.banvor"
         minSdk 21
         targetSdk 31
-        versionCode 2
-        versionName "2.2"
+        versionCode gitVersionCode()
+        versionName gitVersion()
 
         testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
         resValue "bool", "debug_visible", "false"