/*  Title:      Pure/PIDE/text.scala

    Author:     Fabian Immler, TU Munich

    Author:     Makarius

Basic operations on plain text.

*/

package isabelle

object Text

{

  /* offset and range */

  type Offset = Int

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

  /* 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 (is_insert == do_insert) i + text.length

      else (i - text.length) max start

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

    def revert(i: Offset): Offset = transform(false, i)

    /* 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))

      }

  }

}