/*  Title:      Pure/General/scan.scala

     Author:     Makarius

 Efficient scanning of keywords and tokens.

 */

 package isabelle

 import scala.collection.{IndexedSeq, TraversableOnce}

 import scala.collection.immutable.PagedSeq

 import scala.util.parsing.input.{OffsetPosition, Position => InputPosition, Reader}

 import scala.util.parsing.combinator.RegexParsers

 import java.io.{File, BufferedInputStream, FileInputStream}

 object Scan

 {

   /** context of partial scans **/

   sealed abstract class Context

   case object Finished extends Context

   case class Quoted(quote: String) extends Context

   case object Verbatim extends Context

   case class Comment(depth: Int) extends Context

   /** Lexicon -- position tree **/

   object Lexicon

   {

     /* representation */

     sealed case class Tree(val branches: Map[Char, (String, Tree)])

     private val empty_tree = Tree(Map())

     val empty: Lexicon = new Lexicon(empty_tree)

     def apply(elems: String*): Lexicon = empty ++ elems

   }

   final class Lexicon private(main_tree: Lexicon.Tree) extends RegexParsers

   {

     import Lexicon.Tree

     /* auxiliary operations */

     private def content(tree: Tree, result: List[String]): List[String] =

       (result /: tree.branches.toList) ((res, entry) =>

         entry match { case (_, (s, tr)) =>

           if (s.isEmpty) content(tr, res) else content(tr, s :: res) })

     private def lookup(str: CharSequence): Option[(Boolean, Tree)] =

     {

       val len = str.length

       def look(tree: Tree, tip: Boolean, i: Int): Option[(Boolean, Tree)] =

       {

         if (i < len) {

           tree.branches.get(str.charAt(i)) match {

             case Some((s, tr)) => look(tr, !s.isEmpty, i + 1)

             case None => None

           }

         } else Some(tip, tree)

       }

       look(main_tree, false, 0)

     }

     def completions(str: CharSequence): List[String] =

       lookup(str) match {

         case Some((true, tree)) => content(tree, List(str.toString))

         case Some((false, tree)) => content(tree, Nil)

         case None => Nil

       }

     /* pseudo Set methods */

     def iterator: Iterator[String] = content(main_tree, Nil).sorted.iterator

     override def toString: String = iterator.mkString("Lexicon(", ", ", ")")

     def empty: Lexicon = Lexicon.empty

     def isEmpty: Boolean = main_tree.branches.isEmpty

     def contains(elem: String): Boolean =

       lookup(elem) match {

         case Some((tip, _)) => tip

         case _ => false

       }

     /* add elements */

     def + (elem: String): Lexicon =

       if (contains(elem)) this

       else {

         val len = elem.length

         def extend(tree: Tree, i: Int): Tree =

           if (i < len) {

             val c = elem.charAt(i)

             val end = (i + 1 == len)

             tree.branches.get(c) match {

               case Some((s, tr)) =>

                 Tree(tree.branches +

                   (c -> (if (end) elem else s, extend(tr, i + 1))))

               case None =>

                 Tree(tree.branches +

                   (c -> (if (end) elem else "", extend(Lexicon.empty_tree, i + 1))))

             }

           }

           else tree

         new Lexicon(extend(main_tree, 0))

       }

     def ++ (elems: TraversableOnce[String]): Lexicon = (this /: elems)(_ + _)

     /** RegexParsers methods **/

     override val whiteSpace = "".r

     /* optional termination */

     def opt_term[T](p: => Parser[T]): Parser[Option[T]] =

       p ^^ (x => Some(x)) | """\z""".r ^^ (_ => None)

     /* keywords from lexicon */

     def keyword: Parser[String] = new Parser[String]

     {

       def apply(in: Input) =

       {

         val source = in.source

         val offset = in.offset

         val len = source.length - offset

         def scan(tree: Tree, result: String, i: Int): String =

         {

           if (i < len) {

             tree.branches.get(source.charAt(offset + i)) match {

               case Some((s, tr)) => scan(tr, if (s.isEmpty) result else s, i + 1)

               case None => result

             }

           }

           else result

         }

         val result = scan(main_tree, "", 0)

         if (result.isEmpty) Failure("keyword expected", in)

         else Success(result, in.drop(result.length))

       }

     }.named("keyword")

     /* symbol range */

     def symbol_range(pred: Symbol.Symbol => Boolean, min_count: Int, max_count: Int): Parser[String] =

       new Parser[String]

       {

         def apply(in: Input) =

         {

           val start = in.offset

           val end = in.source.length

           val matcher = new Symbol.Matcher(in.source)

           var i = start

           var count = 0

           var finished = false

           while (!finished) {

             if (i < end && count < max_count) {

               val n = matcher(i, end)

               val sym = in.source.subSequence(i, i + n).toString

               if (pred(sym)) { i += n; count += 1 }

               else finished = true

             }

             else finished = true

           }

           if (count < min_count) Failure("bad input", in)

           else Success(in.source.subSequence(start, i).toString, in.drop(i - start))

         }

       }.named("symbol_range")

     def one(pred: Symbol.Symbol => Boolean): Parser[String] =

       symbol_range(pred, 1, 1)

     def many(pred: Symbol.Symbol => Boolean): Parser[String] =

       symbol_range(pred, 0, Integer.MAX_VALUE)

     def many1(pred: Symbol.Symbol => Boolean): Parser[String] =

       symbol_range(pred, 1, Integer.MAX_VALUE)

     /* quoted strings */

     private def quoted_body(quote: Symbol.Symbol): Parser[String] =

     {

       rep(many1(sym => sym != quote && sym != "\\") | "\\" + quote | "\\\\" |

         (("""\\\d\d\d""".r) ^? { case x if x.substring(1, 4).toInt <= 255 => x })) ^^ (_.mkString)

     }

     private def quoted(quote: Symbol.Symbol): Parser[String] =

     {

       quote ~ quoted_body(quote) ~ quote ^^ { case x ~ y ~ z => x + y + z }

     }.named("quoted")

     def quoted_content(quote: Symbol.Symbol, source: String): String =

     {

       require(parseAll(quoted(quote), source).successful)

       val body = source.substring(1, source.length - 1)

       if (body.exists(_ == '\\')) {

         val content =

           rep(many1(sym => sym != quote && sym != "\\") |

               "\\" ~> (quote | "\\" | """\d\d\d""".r ^^ { case x => x.toInt.toChar.toString }))

         parseAll(content ^^ (_.mkString), body).get

       }

       else body

     }

     def quoted_context(quote: Symbol.Symbol, ctxt: Context): Parser[(String, Context)] =

     {

       ctxt match {

         case Finished =>

           quote ~ quoted_body(quote) ~ opt_term(quote) ^^

             { case x ~ y ~ Some(z) => (x + y + z, Finished)

               case x ~ y ~ None => (x + y, Quoted(quote)) }

         case Quoted(q) if q == quote =>

           quoted_body(quote) ~ opt_term(quote) ^^

             { case x ~ Some(y) => (x + y, Finished)

               case x ~ None => (x, ctxt) }

         case _ => failure("")

       }

     }.named("quoted_context")

     /* verbatim text */

     private def verbatim_body: Parser[String] =

       rep(many1(sym => sym != "*") | """\*(?!\})""".r) ^^ (_.mkString)

     private def verbatim: Parser[String] =

     {

       "{*" ~ verbatim_body ~ "*}" ^^ { case x ~ y ~ z => x + y + z }

     }.named("verbatim")

     def verbatim_content(source: String): String =

     {

       require(parseAll(verbatim, source).successful)

       source.substring(2, source.length - 2)

     }

     def verbatim_context(ctxt: Context): Parser[(String, Context)] =

     {

       ctxt match {

         case Finished =>

           "{*" ~ verbatim_body ~ opt_term("*}") ^^

             { case x ~ y ~ Some(z) => (x + y + z, Finished)

               case x ~ y ~ None => (x + y, Verbatim) }

         case Verbatim =>

           verbatim_body ~ opt_term("*}") ^^

             { case x ~ Some(y) => (x + y, Finished)

               case x ~ None => (x, Verbatim) }

         case _ => failure("")

       }

     }.named("verbatim_context")

     /* nested comments */

     private def comment_depth(depth: Int): Parser[(String, Int)] = new Parser[(String, Int)]

     {

       require(depth >= 0)

       val comment_text =

         rep1(many1(sym => sym != "*" && sym != "(") | """\*(?!\))|\((?!\*)""".r)

       def apply(in: Input) =

       {

         var rest = in

         def try_parse[A](p: Parser[A]): Boolean =

         {

           parse(p ^^^ (), rest) match {

             case Success(_, next) => { rest = next; true }

             case _ => false

           }

         }

         var d = depth

         var finished = false

         while (!finished) {

           if (try_parse("(*")) d += 1

           else if (d > 0 && try_parse("*)")) d -= 1

           else if (d == 0 || !try_parse(comment_text)) finished = true

         }

         if (in.offset < rest.offset)

           Success((in.source.subSequence(in.offset, rest.offset).toString, d), rest)

         else Failure("comment expected", in)

       }

     }.named("comment_depth")

     def comment: Parser[String] =

       comment_depth(0) ^? { case (x, d) if d == 0 => x }

     def comment_context(ctxt: Context): Parser[(String, Context)] =

     {

       val depth =

         ctxt match {

           case Finished => 0

           case Comment(d) => d

           case _ => -1

         }

       if (depth >= 0)

         comment_depth(depth) ^^

           { case (x, 0) => (x, Finished)

             case (x, d) => (x, Comment(d)) }

       else failure("")

     }

     def comment_content(source: String): String =

     {

       require(parseAll(comment, source).successful)

       source.substring(2, source.length - 2)

     }

     /* outer syntax tokens */

     private def delimited_token: Parser[Token] =

     {

       val string = quoted("\"") ^^ (x => Token(Token.Kind.STRING, x))

       val alt_string = quoted("`") ^^ (x => Token(Token.Kind.ALT_STRING, x))

       val verb = verbatim ^^ (x => Token(Token.Kind.VERBATIM, x))

       val cmt = comment ^^ (x => Token(Token.Kind.COMMENT, x))

       string | (alt_string | (verb | cmt))

     }

     private def other_token(is_command: String => Boolean)

       : Parser[Token] =

     {

       val id = one(Symbol.is_letter) ~ many(Symbol.is_letdig) ^^ { case x ~ y => x + y }

       val nat = many1(Symbol.is_digit)

       val natdot = nat ~ "." ~ nat ^^ { case x ~ y ~ z => x + y + z }

       val id_nat = id ~ opt("." ~ nat) ^^ { case x ~ Some(y ~ z) => x + y + z case x ~ None => x }

       val ident = id ~ rep("." ~> id) ^^

         { case x ~ Nil => Token(Token.Kind.IDENT, x)

           case x ~ ys => Token(Token.Kind.LONG_IDENT, (x :: ys).mkString(".")) }

       val var_ = "?" ~ id_nat ^^ { case x ~ y => Token(Token.Kind.VAR, x + y) }

       val type_ident = "'" ~ id ^^ { case x ~ y => Token(Token.Kind.TYPE_IDENT, x + y) }

       val type_var = "?'" ~ id_nat ^^ { case x ~ y => Token(Token.Kind.TYPE_VAR, x + y) }

       val nat_ = nat ^^ (x => Token(Token.Kind.NAT, x))

       val float =

         ("-" ~ natdot ^^ { case x ~ y => x + y } | natdot) ^^ (x => Token(Token.Kind.FLOAT, x))

       val sym_ident =

         (many1(Symbol.is_symbolic_char) | one(sym => Symbol.is_symbolic(sym))) ^^

         (x => Token(Token.Kind.SYM_IDENT, x))

       val space = many1(Symbol.is_blank) ^^ (x => Token(Token.Kind.SPACE, x))

       // FIXME check

       val junk = many(sym => !(Symbol.is_blank(sym)))

       val junk1 = many1(sym => !(Symbol.is_blank(sym)))

       val bad_delimiter =

         ("\"" | "`" | "{*" | "(*") ~ junk ^^ { case x ~ y => Token(Token.Kind.UNPARSED, x + y) }

       val bad = junk1 ^^ (x => Token(Token.Kind.UNPARSED, x))

       val command_keyword =

         keyword ^^ (x => Token(if (is_command(x)) Token.Kind.COMMAND else Token.Kind.KEYWORD, x))

       space | (bad_delimiter |

         (((ident | (var_ | (type_ident | (type_var | (float | (nat_ | sym_ident)))))) |||

           command_keyword) | bad))

     }

     def token(is_command: String => Boolean): Parser[Token] =

       delimited_token | other_token(is_command)

     def token_context(is_command: String => Boolean, ctxt: Context): Parser[(Token, Context)] =

     {

       val string =

         quoted_context("\"", ctxt) ^^ { case (x, c) => (Token(Token.Kind.STRING, x), c) }

       val alt_string =

         quoted_context("`", ctxt) ^^ { case (x, c) => (Token(Token.Kind.ALT_STRING, x), c) }

       val verb = verbatim_context(ctxt) ^^ { case (x, c) => (Token(Token.Kind.VERBATIM, x), c) }

       val cmt = comment_context(ctxt) ^^ { case (x, c) => (Token(Token.Kind.COMMENT, x), c) }

       val other = other_token(is_command) ^^ { case x => (x, Finished) }

       string | (alt_string | (verb | (cmt | other)))

     }

   }

   /** read file without decoding -- enables efficient length operation **/

   private class Restricted_Seq(seq: IndexedSeq[Char], start: Int, end: Int)

     extends CharSequence

   {

     def charAt(i: Int): Char =

       if (0 <= i && i < length) seq(start + i)

       else throw new IndexOutOfBoundsException

     def length: Int = end - start  // avoid potentially expensive seq.length

     def subSequence(i: Int, j: Int): CharSequence =

       if (0 <= i && i <= j && j <= length) new Restricted_Seq(seq, start + i, start + j)

       else throw new IndexOutOfBoundsException

     override def toString: String =

     {

       val buf = new StringBuilder(length)

       for (offset <- start until end) buf.append(seq(offset))

       buf.toString

     }

   }

   abstract class Byte_Reader extends Reader[Char] { def close: Unit }

   def byte_reader(file: File): Byte_Reader =

   {

     val stream = new BufferedInputStream(new FileInputStream(file))

     val seq = new PagedSeq(

       (buf: Array[Char], offset: Int, length: Int) =>

         {

           var i = 0

           var c = 0

           var eof = false

           while (!eof && i < length) {

             c = stream.read

             if (c == -1) eof = true

             else { buf(offset + i) = c.toChar; i += 1 }

           }

           if (i > 0) i else -1

         })

     val restricted_seq = new Restricted_Seq(seq, 0, file.length.toInt)

     class Paged_Reader(override val offset: Int) extends Byte_Reader

     {

       override lazy val source: CharSequence = restricted_seq

       def first: Char = if (seq.isDefinedAt(offset)) seq(offset) else '\032'

       def rest: Paged_Reader = if (seq.isDefinedAt(offset)) new Paged_Reader(offset + 1) else this

       def pos: InputPosition = new OffsetPosition(source, offset)

       def atEnd: Boolean = !seq.isDefinedAt(offset)

       override def drop(n: Int): Paged_Reader = new Paged_Reader(offset + n)

       def close { stream.close }

     }

     new Paged_Reader(0)

   }

 }