A Play Framework Evolutions reader that reads a single revision from the class path.

SingleRevisionClassLoaderEvolutionsReader.scala

import play.api.db.evolutions.{ClassLoaderEvolutionsReader, Evolution}
import play.api.libs.Collections

/***
  * Evolutions reader that reads a single revision from the class path.
  *
  * @param revision the revision number to load
  * @param prefix A prefix that gets added to the resource file names
  */
class SingleRevisionClassLoaderEvolutionsReader(val revision: Int, val prefix: String) extends ClassLoaderEvolutionsReader(prefix = prefix) {

  override def evolutions(db: String): Seq[Evolution] = {
    val upsMarker = """^#.*!Ups.*$""".r
    val downsMarker = """^#.*!Downs.*$""".r

    val UPS = "UPS"
    val DOWNS = "DOWNS"
    val UNKNOWN = "UNKNOWN"

    val mapUpsAndDowns: PartialFunction[String, String] = {
      case upsMarker() => UPS
      case downsMarker() => DOWNS
      case _ => UNKNOWN
    }

    val isMarker: PartialFunction[String, Boolean] = {
      case upsMarker() => true
      case downsMarker() => true
      case _ => false
    }

    loadResource(db, revision).map { stream =>
      val script = scala.io.Source.fromInputStream(stream).mkString

      val parsed = Collections.unfoldLeft(("", script.split('\n').toList.map(_.trim))) {
        case (_, Nil) => None
        case (context, lines) => {
          val (some, next) = lines.span(l => !isMarker(l))
          Some((next.headOption.map(c => (mapUpsAndDowns(c), next.tail)).getOrElse("" -> Nil),
            context -> some.mkString("\n")))
        }
      }.reverse.drop(1).groupBy(i => i._1).mapValues { _.map(_._2).mkString("\n").trim }

      Evolution(
        revision,
        parsed.getOrElse(UPS, ""),
        parsed.getOrElse(DOWNS, ""))
    }.toList
  }
}

object SingleRevisionClassLoaderEvolutionsReader {
  def apply(revision: Int, prefix: String = "") = new SingleRevisionClassLoaderEvolutionsReader(revision, prefix)
}