/*  Title:      Pure/PIDE/text.scala

     Author:     Fabian Immler, TU Munich

     Author:     Makarius

 Basic operations on plain text.

 */

 package isabelle

 object Text

 {

   /* offset */

   type Offset = Int

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

   object Range

   {

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

   }

   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 restrict(that: Range): Range =

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

   }

   /* information associated with text range */

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

   {

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

   }

   /* 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(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))

       }

   }

 }