sbt-gs-calver/src/main/scala/gs/CalVer.scala

package gs

import java.time.LocalDate
import scala.collection.mutable.ListBuffer

/** Representation of a rendered Calendar Version.
  *
  * @param value
  *   The version string.
  * @param pattern
  *   The pattern which rendered the version string.
  */
case class CalVer(
  value: String,
  pattern: CalVer.Pattern
)

object CalVer {

  /** Render the given pattern to a Calendar Version.
    *
    * @param pattern
    *   The pattern to render.
    * @return
    *   The rendered CalVer value.
    */
  def render(pattern: Pattern): CalVer = {
    val today = LocalDate.now()
    CalVer(
      value = pattern.items.map {
        case Left(component) =>
          component match {
            case Component.YYYY           => today.getYear().toString()
            case Component.MM             => today.getMonthValue().toString()
            case Component.DD             => today.getDayOfMonth().toString()
            case Component.Label(label)   => label
            case Component.GitSha(length) => Git.getSha(length)
          }
        case Right(delimiter) => Delimiter.render(delimiter)
      }.mkString,
      pattern = pattern
    )
  }

  object Defaults {

    /** Default pattern for release versions.
      */
    val ReleasePattern: Pattern =
      Pattern
        .builder(Component.YYYY)
        .addDelimiter(Delimiter.Dot)
        .addComponent(Component.MM)
        .addDelimiter(Delimiter.Dot)
        .addComponent(Component.DD)
        .addDelimiter(Delimiter.Hyphen)
        .addComponent(Component.Label("v"))
        .addComponent(Component.GitSha(7))
        .build()

    /** Default pattern for pre-release versions.
      */
    val PreReleasePattern: Pattern =
      Pattern
        .builder(Component.YYYY)
        .addDelimiter(Delimiter.Dot)
        .addComponent(Component.MM)
        .addDelimiter(Delimiter.Dot)
        .addComponent(Component.DD)
        .addDelimiter(Delimiter.Hyphen)
        .addComponent(Component.GitSha(7))
        .addDelimiter(Delimiter.Hyphen)
        .addComponent(Component.Label("SNAPSHOT"))
        .build()

  }

  sealed trait Component

  object Component {

    /** CalVer Component: Year.
      */
    case object YYYY extends Component

    /** CalVer Component: Month (1-12), without a leading zero.
      */
    case object MM extends Component

    /** CalVer Component: Day of Month, without a leading zero.
      */
    case object DD extends Component

    /** CalVer Component: Label.
      *
      * This component contains an arbitrary string value.
      *
      * @param value
      *   The value of the label.
      */
    case class Label(value: String) extends Component

    /** CalVer Component. Git SHA.
      *
      * This component defines the length (first N characters) of the Git SHA to
      * take from the current branch of the current repository. An empty string
      * is used if lookup fails or no commits exist.
      *
      * @param length
      *   The number of characters of the Git SHA to use.
      */
    case class GitSha(length: Int) extends Component

    def describe(component: Component): String = component match {
      case YYYY           => "YYYY"
      case MM             => "MM"
      case DD             => "DD"
      case Label(value)   => value
      case GitSha(length) => s"SHA($length)"
    }

  }

  sealed abstract class Delimiter(val value: String)

  object Delimiter {
    case object Dot        extends Delimiter(".")
    case object Hyphen     extends Delimiter("-")
    case object Plus       extends Delimiter("+")
    case object Underscore extends Delimiter("_")

    def render(delimiter: Delimiter): String = delimiter.value
  }

  final class Pattern private (val items: List[Pattern.Item]) {

    lazy val str: String =
      items.map {
        case Left(component)  => Component.describe(component)
        case Right(delimiter) => Delimiter.render(delimiter)
      }.mkString

    override def toString(): String = str
  }

  object Pattern {
    private type Item = Either[Component, Delimiter]

    def builder(component: Component): Builder = Builder(component)

    final class Builder private () {
      private val buffer: ListBuffer[Item] = new ListBuffer()

      def addComponent(component: Component): Builder = {
        val _ = buffer.append(Left(component))
        this
      }

      def addDelimiter(delimiter: Delimiter): Builder = {
        val _ = buffer.append(Right(delimiter))
        this
      }

      def build(): Pattern = new Pattern(buffer.toList)
    }

    object Builder {

      def apply(component: Component): Builder = {
        val b = new Builder()
        b.addComponent(component)
        b
      }

    }

  }

}