/*  Title:      Pure/General/symbol.scala

    Author:     Makarius

Detecting and recoding Isabelle symbols.

*/

package isabelle

import scala.io.Source

import scala.collection.{jcl, mutable}

import scala.util.matching.Regex

object Symbol

{

  /* Symbol regexps */

  private val plain = new Regex("""(?xs)

    [^\\ \ud800-\udfff] | [\ud800-\udbff][\udc00-\udfff] """)

  private val symbol = new Regex("""(?xs)

      \\ < (?:

      \^? [A-Za-z][A-Za-z0-9_']* |

      \^raw: [\x20-\x7e\u0100-\uffff && [^.>]]* ) >""")

  private val bad_symbol = new Regex("(?xs) (?!" + symbol + ")" +

    """ \\ < (?: (?! \s | [\"`\\] | \(\* | \*\) | \{\* | \*\} ) . )*""")

  // total pattern

  val regex = new Regex(plain + "|" + symbol + "|" + bad_symbol + "| .")

  // prefix of another symbol

  def is_open(s: CharSequence): Boolean =

  {

    val len = s.length

    len == 1 && Character.isHighSurrogate(s.charAt(0)) ||

    s == "\\" ||

    s == "\\<" ||

    len > 2 && s.charAt(len - 1) != '>'

  }

  /* elements */

  private def could_open(c: Char): Boolean =

    c == '\\' || Character.isHighSurrogate(c)

  def elements(text: CharSequence) = new Iterator[String] {

    private val matcher = regex.pattern.matcher(text)

    private var i = 0

    def hasNext = i < text.length

    def next = {

      val len =

        if (could_open(text.charAt(i))) {

          matcher.region(i, text.length).lookingAt

          matcher.group.length

        }

        else 1

      val s = text.subSequence(i, i + len)

      i += len

      s.toString

    }

  }

  /* decoding offsets */

  class Index(text: CharSequence)

  {

    case class Entry(chr: Int, sym: Int)

    val index: Array[Entry] =

    {

      val matcher = regex.pattern.matcher(text)

      val buf = new mutable.ArrayBuffer[Entry]

      var chr = 0

      var sym = 0

      while (chr < text.length) {

        val len =

          if (could_open(text.charAt(chr))) {

            matcher.region(chr, text.length).lookingAt

            matcher.group.length

          }

          else 1

        chr += len

        sym += 1

        if (len > 1) buf += Entry(chr, sym)

      }

      buf.toArray

    }

    def decode(sym: Int): Int =

    {

      val end = index.length

      def bisect(a: Int, b: Int): Int =

      {

        if (a < b) {

          val c = (a + b) / 2

          if (sym < index(c).sym) bisect(a, c)

          else if (c + 1 == end || sym < index(c + 1).sym) c

          else bisect(c + 1, b)

        }

        else -1

      }

      val i = bisect(0, end)

      if (i < 0) sym

      else index(i).chr + sym - index(i).sym

    }

  }

  /* recoding text */

  private class Recoder(list: List[(String, String)])

  {

    private val (min, max) =

    {

      var min = '\uffff'

      var max = '\u0000'

      for ((x, _) <- list) {

        val c = x(0)

        if (c < min) min = c

        if (c > max) max = c

      }

      (min, max)

    }

    private val table =

    {

      val table = new jcl.HashMap[String, String]   // reasonably efficient?

      for ((x, y) <- list) table + (x -> y)

      table

    }

    def recode(text: String): String =

    {

      val len = text.length

      val matcher = regex.pattern.matcher(text)

      val result = new StringBuilder(len)

      var i = 0

      while (i < len) {

        val c = text(i)

        if (min <= c && c <= max) {

          matcher.region(i, len).lookingAt

          val x = matcher.group

          result.append(table.get(x) getOrElse x)

          i = matcher.end

        }

        else { result.append(c); i += 1 }

      }

      result.toString

    }

  }

  /** Symbol interpretation **/

  class Interpretation(symbol_decls: Iterator[String])

  {

    /* read symbols */

    private val empty = new Regex("""(?xs) ^\s* (?: \#.* )? $ """)

    private val key = new Regex("""(?xs) (.+): """)

    private def read_decl(decl: String): (String, Map[String, String]) =

    {

      def err() = error("Bad symbol declaration: " + decl)

      def read_props(props: List[String]): Map[String, String] =

      {

        props match {

          case Nil => Map()

          case _ :: Nil => err()

          case key(x) :: y :: rest => read_props(rest) + (x -> y)

          case _ => err()

        }

      }

      decl.split("\\s+").toList match {

        case Nil => err()

        case sym :: props => (sym, read_props(props))

      }

    }

    private val symbols: List[(String, Map[String, String])] =

      for (decl <- symbol_decls.toList if !empty.pattern.matcher(decl).matches)

        yield read_decl(decl)

    /* misc properties */

    val names: Map[String, String] = {

      val name = new Regex("""\\<([A-Za-z][A-Za-z0-9_']*)>""")

      Map((for ((sym @ name(a), _) <- symbols) yield (sym -> a)): _*)

    }

    val abbrevs: Map[String, String] = Map((

      for ((sym, props) <- symbols if props.isDefinedAt("abbrev"))

        yield (sym -> props("abbrev"))): _*)

    /* main recoder methods */

    private val (decoder, encoder) =

    {

      val mapping =

        for {

          (sym, props) <- symbols

          val code =

            try { Integer.decode(props("code")).intValue }

            catch {

              case _: NoSuchElementException => error("Missing code for symbol " + sym)

              case _: NumberFormatException => error("Bad code for symbol " + sym)

            }

          val ch = new String(Character.toChars(code))

        } yield (sym, ch)

      (new Recoder(mapping),

       new Recoder(mapping map { case (x, y) => (y, x) }))

    }

    def decode(text: String): String = decoder.recode(text)

    def encode(text: String): String = encoder.recode(text)

  }

}