import org.gradle.api.internal.artifacts.repositories.layout.IvyRepositoryLayout
import java.io.InputStream
import java.util.zip.*

object Attributes {
    val artifactType = Attribute.of("artifactType", String::class.java)
    val zipType = "zip"
    val jars = "jars"
}

/**
 * Extracts all jars from a Gradle binary distribution.
 */
class ExtractGradleJars : ArtifactTransform() {

    override fun transform(input: File): List<File> {
        unzipTo(outputDirectory, input)
        return outputDirectory
            .walkTopDown()
            .filter { it.isFile && it.extension == "jar" }
            .toList()
    }

    private
    fun unzipTo(outputDirectory: File, zipFile: File) {
        ZipFile(zipFile).use { zip ->
            for (entry in zip.entries()) {
                unzipEntryTo(outputDirectory, zip, entry)
            }
        }
    }

    private
    fun unzipEntryTo(outputDirectory: File, zip: ZipFile, entry: ZipEntry) {
        val output = File(outputDirectory, entry.name)
        if (entry.isDirectory) {
            output.mkdirs()
        } else {
            zip.getInputStream(entry).use { it.copyTo(output) }
        }
    }

    private
    fun InputStream.copyTo(file: File): Long =
        file.outputStream().use { copyTo(it) }
}

val gradleDistribution by configurations.creating {
    attributes {
       attribute(Attributes.artifactType, Attributes.jars)
    }
}

dependencies {

    registerTransform {
        from.attribute(Attributes.artifactType, Attributes.zipType)
        to.attribute(Attributes.artifactType, Attributes.jars)
        artifactTransform(ExtractGradleJars::class.java)
    }

    gradleDistribution(
        group = "gradle",
        name = "gradle",
        version = "4.3.1",
        configuration = null,
        classifier = "bin",
        ext = "zip")
}

repositories {
    ivy {
        name = "Gradle distributions"
        url = uri("https://services.gradle.org/distributions")
        layout("pattern") {
            this as IvyPatternRepositoryLayout
            artifact("[module]-[revision](-[classifier])(.[ext])")
        }
    }
}

tasks {
    "printJarNames" {
        doLast {
            println(gradleDistribution.files.map { it.name })
        }
    }
}