import org.gradle.api.file.FileCollection
import java.io.OutputStream.nullOutputStream
import java.security.DigestOutputStream
import java.security.MessageDigest
import java.util.*

fun checksumFiles(
  files: FileCollection,
  includes: List<String> = emptyList(),
  excludes: List<String> = emptyList(),
): String {
  val content = files.asFileTree.matching {
    include(includes)
    exclude(excludes)
  }

  val messageDigester = MessageDigest.getInstance("SHA-256")

  DigestOutputStream(nullOutputStream(), messageDigester).use { digestStream ->
    content.visit {
      // hash relative path, based on the common root dir of all files in the FileCollection
      digestStream.write(relativePath.pathString.toByteArray())

      // hash file content
      file.inputStream().use { fis ->
        fis.copyTo(digestStream)
      }
    }
  }

  return Base64.getEncoder().encodeToString(messageDigester.digest())
}