import sbt._
import sbt.Keys._
import sbtrelease.Version
import com.typesafe.sbt.SbtGit._

object GitVersion {

  // Base version for master branch
  private val baseVersion = "v1.5.x"

  // 0.1.x
  private val versionBranch = """v?([0-9\.]+)(?:\.x)?""".r

  // v0.1.47-31-g230560c
  // v0.1.47-20150807.161518-9
  private val snapshotVersion = """v?([0-9\.]+)-(?:\d+)-(?:[0-9a-z]+)""".r

  // 1.5.0-rc.1-123-gcbfe51a
  private val candidateVersion = """v?([0-9\.]+)(?:-rc\.\d+)?-(?:\d+)-(?:[0-9a-z]+)""".r

  // v0.1.47
  // 1.5.0-rc.1
  private val releaseVersion = """v?([0-9\.]+(?:-rc\.\d+)?)""".r

  /**
   * Needs to check for "false", don't assume it will ever be set to "true".
   * http://docs.travis-ci.com/user/environment-variables/#Default-Environment-Variables
   */
  private def isPullRequest: Boolean = sys.env.getOrElse("TRAVIS_PULL_REQUEST", "false") != "false"

  /**
   * Bump the last git described version to use for the current snapshot. If it is a version branch
   * and the prefix doesn't match, then it is the first snapshot for the branch so use the branch
   * version to start with. 
   */
  private def toSnapshotVersion(branch: String, v: String): String = {
    val v2 = Version(v).map(_.bump.string).getOrElse(v)
    val suffix = "-SNAPSHOT"
    branch match {
      case versionBranch(b) if !v2.startsWith(b) =>
        s"${Version(s"$b.0").map(_.string).getOrElse(v2)}$suffix"
      case _ =>
        s"$v2$suffix"
    }
  }

  lazy val settings: Seq[Def.Setting[_]] = Seq(
    version in ThisBuild := {
      val branch = sys.env.getOrElse("TRAVIS_BRANCH", git.gitCurrentBranch.value)
      val branchVersion = if (branch == "master") baseVersion else branch
      git.gitDescribedVersion.value getOrElse "0.1-SNAPSHOT" match {
        case _ if isPullRequest       => s"0.0.0-PULLREQUEST"
        case snapshotVersion(v)       => toSnapshotVersion(branchVersion, v)
        case candidateVersion(v)      => s"$v-SNAPSHOT"
        case releaseVersion(v)        => v
        case v                        => v
      }
    }
  )
}