jobs/build: use default target when job is triggered by timer

In a nightly build the job parameter TARGET stays on "selected...".
Thus, a check verifies if the job is triggered by a timer and then
takes the default target which is the first one in the file
'nwlTargets'.
With it the description name of the build gets a postfix 'nightly'.

Signed-off-by: Marc Mattmüller <marc.mattmueller@netmodule.com>

jobs/Jenkinsfile_Build

@@ -112,24 +112,51 @@ def printJobParameters() {
     DEBUGGING         = ${params.DEBUGGING}\n\
 ----------------------------------\n"
 }
+
+//---------------------------------------------------------------------------------------------------------------------
+def isJobTriggeredByTimer() {
+  // The following check is not allowed without having an Administrator approved the script signature
+  //   return (currentBuild.rawBuild.getCause(hudson.triggers.TimerTrigger$TimerTriggerCause) != null)
+  // Thus we need to find another way round with:
+  //   CAUSE = "${currentBuild.getBuildCauses()[0].shortDescription}"
+  def jobCause = currentBuild.getBuildCauses()
+  println "jobCause as information:\n" + jobCause
+  def jobDescriptionString = "${jobCause[0].shortDescription}"
+  return jobDescriptionString.contains("timer")
+}
+//---------------------------------------------------------------------------------------------------------------------
+def getDefaultTarget() {
+  def defaultTarget = sh(returnStdout: true, script: "head -n2 ./jobs/nwlTargets | tail -n1").trim()
+  return "${defaultTarget}"
+}
 //---------------------------------------------------------------------------------------------------------------------
 def checkJobParameters() {
-  println "ToDo: Check if triggered by timer before throwing error"
+  // Check the selected target and overwrite it with a default one when triggered by a timer
+  def selectedTarget = "${params.TARGET}"
   if("${params.TARGET}" == "select...") {
-    currentBuild.result = 'ABORTED'
-    error("Missing build target --> select parameter TARGET for a proper build")
+    selectedTarget = ""
+    if(isJobTriggeredByTimer()) {
+      selectedTarget = getDefaultTarget()
+      println "Triggered by Timer --> taking default target = ${selectedTarget}"
+    }
+    else {
+      currentBuild.result = 'ABORTED'
+      error("Missing build target --> select parameter TARGET for a proper build")
+    }
   }
+  env.TARGET = "${selectedTarget}"
 }
 //---------------------------------------------------------------------------------------------------------------------
 def setDisplayName() {
   def buildName = "#${env.BUILD_NUMBER}"
-  currentBuild.displayName = "${buildName}-${params.TARGET}"
+  def postfix = isJobTriggeredByTimer() ? "-nightly" : ""
+  currentBuild.displayName = "${buildName}-${env.TARGET}${postfix}"
 }
 
 
 //---------------------------------------------------------------------------------------------------------------------
 def setupEnvironment(commonHelpers) {
-  def machine = "${params.TARGET}"
+  def machine = "${env.TARGET}"
   def nwlBranch = "${params.BUILD_BRANCH}"
   def nwlRepoDir = "${env.YOCTO_REPO_DIR}"
   commonHelpers.setupBuildEnvironment(machine, nwlBranch, nwlRepoDir, params.DEBUGGING)