/*  Title:      Pure/General/path.scala

    Author:     Makarius

Algebra of file-system paths: basic POSIX notation, extended by named

roots (e.g. //foo) and variables (e.g. $BAR).

*/

package isabelle

import java.io.{File => JFile}

import scala.util.matching.Regex

object Path

{

  /* path elements */

  sealed abstract class Elem

  private case class Root(val name: String) extends Elem

  private case class Basic(val name: String) extends Elem

  private case class Variable(val name: String) extends Elem

  private case object Parent extends Elem

  private def err_elem(msg: String, s: String): Nothing =

    error (msg + " path element specification: " + quote(s))

  private def check_elem(s: String): String =

    if (s == "" || s == "~" || s == "~~") err_elem("Illegal", s)

    else

      s.iterator.filter(c => c == '/' || c == '\\' || c == '$' || c == ':').toList match {

        case Nil => s

        case bads =>

          err_elem ("Illegal character(s) " + commas_quote(bads.map(_.toString)) + " in", s)

      }

  private def root_elem(s: String): Elem = Root(check_elem(s))

  private def basic_elem(s: String): Elem = Basic(check_elem(s))

  private def variable_elem(s: String): Elem = Variable(check_elem(s))

  private def apply_elem(y: Elem, xs: List[Elem]): List[Elem] =

    (y, xs) match {

      case (Root(_), _) => List(y)

      case (Parent, Root(_) :: _) => xs

      case (Parent, Basic(_) :: rest) => rest

      case _ => y :: xs

    }

  private def norm_elems(elems: List[Elem]): List[Elem] =

    (elems :\ (Nil: List[Elem]))(apply_elem)

  private def implode_elem(elem: Elem): String =

    elem match {

      case Root("") => ""

      case Root(s) => "//" + s

      case Basic(s) => s

      case Variable(s) => "$" + s

      case Parent => ".."

    }

  /* path constructors */

  val current: Path = new Path(Nil)

  val root: Path = new Path(List(Root("")))

  def named_root(s: String): Path = new Path(List(root_elem(s)))

  def basic(s: String): Path = new Path(List(basic_elem(s)))

  def variable(s: String): Path = new Path(List(variable_elem(s)))

  val parent: Path = new Path(List(Parent))

  /* explode */

  private def explode_elem(s: String): Elem =

    if (s == "..") Parent

    else if (s == "~") Variable("USER_HOME")

    else if (s == "~~") Variable("ISABELLE_HOME")

    else if (s.startsWith("$")) variable_elem(s.substring(1))

    else basic_elem(s)

  private def explode_elems(ss: List[String]): List[Elem] =

    ss.filterNot(s => s.isEmpty || s == ".").map(explode_elem).reverse

  def explode(str: String): Path =

  {

    val ss = space_explode('/', str)

    val r = ss.takeWhile(_.isEmpty).length

    val es = ss.dropWhile(_.isEmpty)

    val (roots, raw_elems) =

      if (r == 0) (Nil, es)

      else if (r == 1) (List(Root("")), es)

      else if (es.isEmpty) (List(Root("")), Nil)

      else (List(root_elem(es.head)), es.tail)

    new Path(norm_elems(explode_elems(raw_elems) ++ roots))

  }

  def split(str: String): List[Path] =

    space_explode(':', str).filterNot(_.isEmpty).map(explode)

}

final class Path private(private val elems: List[Path.Elem]) // reversed elements

{

  def is_current: Boolean = elems.isEmpty

  def is_absolute: Boolean = !elems.isEmpty && elems.last.isInstanceOf[Path.Root]

  def is_basic: Boolean = elems match { case List(Path.Basic(_)) => true case _ => false }

  def +(other: Path): Path = new Path((other.elems :\ elems)(Path.apply_elem))

  /* implode */

  def implode: String =

    elems match {

      case Nil => "."

      case List(Path.Root("")) => "/"

      case _ => elems.map(Path.implode_elem).reverse.mkString("/")

    }

  override def toString: String = quote(implode)

  /* base element */

  private def split_path: (Path, String) =

    elems match {

      case Path.Basic(s) :: xs => (new Path(xs), s)

      case _ => error("Cannot split path into dir/base: " + toString)

    }

  def dir: Path = split_path._1

  def base: Path = new Path(List(Path.Basic(split_path._2)))

  def ext(e: String): Path =

    if (e == "") this

    else {

      val (prfx, s) = split_path

      prfx + Path.basic(s + "." + e)

    }

  private val Ext = new Regex("(.*)\\.([^.]*)")

  def split_ext: (Path, String) =

  {

    val (prefix, base) = split_path

    base match {

      case Ext(b, e) => (prefix + Path.basic(b), e)

      case _ => (Path.basic(base), "")

    }

  }

  /* expand */

  def expand: Path =

  {

    def eval(elem: Path.Elem): List[Path.Elem] =

      elem match {

        case Path.Variable(s) =>

          Path.explode(Isabelle_System.getenv_strict(s)).elems

        case x => List(x)

      }

    new Path(Path.norm_elems(elems.map(eval).flatten))

  }

  /* platform file */

  def file: JFile = Isabelle_System.platform_file(this)

}