def getGitHash = { ->
  def stdout = new ByteArrayOutputStream()
  exec {
    commandLine 'git', 'rev-parse', '--short', 'HEAD'
    standardOutput = stdout
  }
  return stdout.toString().trim()
}

tasks.register("writeVersionNumberFile") {

  def versionFile = file("${sourceSets.main.output.resourcesDir}/${project.name}.version")
  inputs.property "version", project.version
  outputs.file versionFile

  doFirst {
    assert versionFile.parentFile.mkdirs() || versionFile.parentFile.directory
    versionFile.text = "${project.version}~${getGitHash()}"
  }
}

compileJava.dependsOn writeVersionNumberFile