/*  Title:      Pure/PIDE/text.scala

     Author:     Fabian Immler, TU Munich

     Author:     Makarius

 Basic operations on plain text.

 */

 package isabelle

 import scala.collection.mutable

 import scala.math.Ordering

 import scala.util.Sorting

 object Text

 {

   /* offset */

   type Offset = Int

   /* range -- with total quasi-ordering */

   object Range

   {

     def apply(start: Offset): Range = Range(start, start)

     object Ordering extends scala.math.Ordering[Text.Range]

     {

       def compare(r1: Text.Range, r2: Text.Range): Int = r1 compare r2

     }

   }

   sealed case class Range(val start: Offset, val stop: Offset)

   {

     // denotation: {start} Un {i. start < i & i < stop}

     if (start > stop)

       error("Bad range: [" + start.toString + ":" + stop.toString + "]")

     override def toString = "[" + start.toString + ":" + stop.toString + "]"

     def map(f: Offset => Offset): Range = Range(f(start), f(stop))

     def +(i: Offset): Range = map(_ + i)

     def -(i: Offset): Range = map(_ - i)

     def is_singularity: Boolean = start == stop

     def contains(i: Offset): Boolean = start == i || start < i && i < stop

     def contains(that: Range): Boolean = this.contains(that.start) && that.stop <= this.stop

     def overlaps(that: Range): Boolean = this.contains(that.start) || that.contains(this.start)

     def compare(that: Range): Int = if (overlaps(that)) 0 else this.start compare that.start

     def apart(that: Range): Boolean =

       (this.start max that.start) > (this.stop min that.stop)

     def restrict(that: Range): Range =

       Range(this.start max that.start, this.stop min that.stop)

     def try_restrict(that: Range): Option[Range] =

       if (this apart that) None

       else Some(restrict(that))

     def try_join(that: Range): Option[Range] =

       if (this apart that) None

       else Some(Range(this.start min that.start, this.stop max that.stop))

   }

   /* perspective */

   object Perspective

   {

     val empty: Perspective = Perspective(Nil)

     def apply(ranges: Seq[Range]): Perspective =

     {

       val result = new mutable.ListBuffer[Text.Range]

       var last: Option[Text.Range] = None

       def ship(next: Option[Range]) { result ++= last; last = next }

       for (range <- ranges.sortBy(_.start))

       {

         last match {

           case None => ship(Some(range))

           case Some(last_range) =>

             last_range.try_join(range) match {

               case None => ship(Some(range))

               case joined => last = joined

             }

         }

       }

       ship(None)

       new Perspective(result.toList)

     }

   }

   class Perspective private(val ranges: List[Range]) // visible text partitioning in canonical order

   {

     def is_empty: Boolean = ranges.isEmpty

     def range: Range =

       if (is_empty) Range(0)

       else Range(ranges.head.start, ranges.last.stop)

     override def toString = ranges.toString

   }

   /* information associated with text range */

   sealed case class Info[A](val range: Text.Range, val info: A)

   {

     def restrict(r: Text.Range): Info[A] = Info(range.restrict(r), info)

     def try_restrict(r: Text.Range): Option[Info[A]] =

       try { Some(Info(range.restrict(r), info)) }

       catch { case ERROR(_) => None }

   }

   type Markup = Info[XML.Elem]

   /* editing */

   object Edit

   {

     def insert(start: Offset, text: String): Edit = new Edit(true, start, text)

     def remove(start: Offset, text: String): Edit = new Edit(false, start, text)

   }

   class Edit private(val is_insert: Boolean, val start: Offset, val text: String)

   {

     override def toString =

       (if (is_insert) "Insert(" else "Remove(") + (start, text).toString + ")"

     /* transform offsets */

     private def transform(do_insert: Boolean, i: Offset): Offset =

       if (i < start) i

       else if (do_insert) i + text.length

       else (i - text.length) max start

     def convert(i: Offset): Offset = transform(is_insert, i)

     def revert(i: Offset): Offset = transform(!is_insert, i)

     def convert(range: Range): Range = range.map(convert)

     def revert(range: Range): Range = range.map(revert)

     /* edit strings */

     private def insert(i: Offset, string: String): String =

       string.substring(0, i) + text + string.substring(i)

     private def remove(i: Offset, count: Int, string: String): String =

       string.substring(0, i) + string.substring(i + count)

     def can_edit(string: String, shift: Int): Boolean =

       shift <= start && start < shift + string.length

     def edit(string: String, shift: Int): (Option[Edit], String) =

       if (!can_edit(string, shift)) (Some(this), string)

       else if (is_insert) (None, insert(start - shift, string))

       else {

         val i = start - shift

         val count = text.length min (string.length - i)

         val rest =

           if (count == text.length) None

           else Some(Edit.remove(start, text.substring(count)))

         (rest, remove(i, count, string))

       }

   }

 }