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package coursier.util

import scala.collection.mutable.ArrayBuffer

object Tree {

  def apply[A](roots: IndexedSeq[A])(children: A => Seq[A]) =
    new Tree(roots, children)

}

final class Tree[A](val roots: IndexedSeq[A], val children: A => Seq[A]) {

  def render(show: A => String): String =
    customRender()(show)

  def customRender(
    assumeTopRoot: Boolean = true,
    extraPrefix: String = "",
    extraSeparator: Option[String] = None
  )(show: A => String): String = {

    /** Recursively go down the resolution for the elems to construct the tree for print out.
      *
      * @param elems
      *   Seq of Elems that have been resolved
      * @param ancestors
      *   a set of Elems to keep track for cycle detection
      * @param prefix
      *   prefix for the print out
      * @param acc
      *   accumulation method on a string
      */
    def recursivePrint(
      elems: Seq[A],
      ancestors: Set[A],
      prefix: String,
      isRoot: Boolean,
      acc: String => Unit
    ): Unit = {
      val unseenElems: Seq[A] = elems.filterNot(ancestors.contains)
      val unseenElemsLen      = unseenElems.length
      for ((elem, idx) <- unseenElems.iterator.zipWithIndex) {
        val isLast = idx == unseenElemsLen - 1
        val tee    = if (!assumeTopRoot && isRoot) "" else if (isLast) "└─ " else "├─ "
        acc(prefix + tee + show(elem))

        val extraPrefix = if (!assumeTopRoot && isRoot) "" else if (isLast) "   " else "│  "
        recursivePrint(children(elem), ancestors + elem, prefix + extraPrefix, isRoot = false, acc)

        for (sep <- extraSeparator)
          if (!assumeTopRoot && isRoot)
            acc(sep)
      }
    }

    val b = new ArrayBuffer[String]
    recursivePrint(roots, Set(), extraPrefix, isRoot = true, b += _)
    b.mkString(System.lineSeparator())
  }

}