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package extensions

import com.android.build.gradle.AppExtension
import com.android.build.gradle.BaseExtension
import com.android.build.gradle.FeatureExtension
import com.android.build.gradle.LibraryExtension
import com.android.build.gradle.api.BaseVariant
import org.gradle.api.DomainObjectSet
import org.gradle.api.GradleException
import org.gradle.api.Project

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<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <View
        android:id="@+id/color_1_view"

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<color name="color1"/>
<color name="color2"/>
<color name="color3"/>

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apply plugin: 'MyFirstPlugin'

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gradlePlugin {
  plugins {
     create("MyFirstPlugin") {
        id = "MyFirstPlugin"
        implementationClass = "MyFirstPlugin"
     }
  }
}

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class MyFirstPlugin : Plugin<Project> {

   override fun apply(project: Project) {
       project.android().variants().all { variant ->

           // Make a task for each combination of build type and product flavor
           val myTask = "myFirstTask${variant.name.capitalize()}"

           // Register a simple task as a lambda. We can later move this to its own  
           // class to make our code cleaner and also add some niceties.

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fun Project.android(): BaseExtension {
   val android = project.extensions.findByType(BaseExtension::class.java)
   if (android != null) {
       return android
   } else {
       throw GradleException("Project $name is not an Android project")
   }
}

fun BaseExtension.variants(): DomainObjectSet<out BaseVariant> {

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class MyFirstPlugin : Plugin<Project> {
   override fun apply(project: Project) {
       // Magic goes here
   }
}

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apply plugin: 'java-gradle-plugin' // Allows us to create and configure custom plugins
apply plugin: 'kotlin' //Needed as we'll write our plugin in Kotlin

buildscript {
  ext.kotlin_version = '1.3.71'
  ext.gradle_version = '3.5.3'
  repositories {
     google()
     jcenter()
  }

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rootProject.name='PluginSample'
include ':app', 'buildSrc'