How to dynamically set appengine gradle property - google-app-engine

Question

How can I create a task that dynamically set app engine project id and run the appengineDeploy task?
On this example when I run deployStaging appengineDeploy is being executed with project 'a', how I can rewrite this code to make it run with project 'b'?
buildscript {
dependencies {
classpath("com.google.cloud.tools:appengine-gradle-plugin:2.0.1")
}
}
apply plugin: 'com.google.cloud.tools.appengine'
def gcpProject = 'a'
appengine {
deploy {
projectId = gcpProject
}
}
task deployStaging() {
doLast {
gcpProject = 'b'
}
}
deployStaging.finalizedBy appengineDeploy

Answer 1

Answer provided by the gradle plugin folks:
appengine {
deploy {
version = "123"
// do not define projectId here
}
}
task deployStaging {
dependsOn appengineDeploy
}
task deployProduction {
dependsOn appengineDeploy
}
// here's the weird gradle logic, use at your own risk
if (project.gradle.startParameter.taskNames.contains("deployStaging")) {
appengine.deploy.projectId = "potato-stage"
}
else if(project.gradle.startParameter.taskNames.contains("deployProduction")) {
appengine.deploy.projectId = "tomato-prod"
}

Answer 2

How about using a project property instead? Project properties can be passed via -P command line parameters:
buildscript {
dependencies {
classpath("com.google.cloud.tools:appengine-gradle-plugin:2.0.1")
}
}
apply plugin: 'com.google.cloud.tools.appengine'
def gcpProject = project.findProperty('stageName') ?: 'a'
appengine {
deploy {
projectId = gcpProject
}
}
Now if you just call ./gradlew appengineDeploy the gcpProject variable will have the value 'a'. If you call ./gradlew appengineDeploy -PstageName=b the gcpProject variable will have the value 'b'.