package org.example

import com.github.h0tk3y.betterParse.combinators.*
import com.github.h0tk3y.betterParse.grammar.Grammar
import com.github.h0tk3y.betterParse.grammar.parser
import com.github.h0tk3y.betterParse.lexer.literalToken
import com.github.h0tk3y.betterParse.lexer.regexToken
import com.github.h0tk3y.betterParse.parser.Parser

class RegexParser : Grammar<RegexItem>() {
  val postfixOperator by regexToken("[+*?]")
  val alternationSymbol by literalToken("|")
  val openParenSymbol by literalToken("(")
  val closeParenSymbol by literalToken(")")

  val dot by literalToken(".")
  val charToken by regexToken("[a-zA-Z0-9]")

  val char by charToken map { CharItem(it.text) }

  val item: Parser<RegexItem> by
          char or
                  (dot asJust DotItem()) or
                  (skip(openParenSymbol) and (parser(::rootParser)) and skip(closeParenSymbol))

  val term: Parser<RegexItem> by
          (item and optional(postfixOperator)) map
                  { result ->
                    result.t1.let { first ->
                      result.t2?.let {
                        when (it.text) {
                          "+" -> PlusItem(first)
                          "*" -> StarItem(first)
                          "?" -> QuestionItem(first)
                          else -> first
                        }
                      }
                              ?: first
                    }
                  }
  val andThen: Parser<RegexItem> by
          oneOrMore(term) map { items -> items.reduce { left, right -> AndThenItem(left, right) } }
  val termWithAlternation: Parser<RegexItem> by
          leftAssociative(
                  andThen,
                  alternationSymbol,
          ) { left, _, right -> AlternationItem(left, right) }

  override val rootParser: Parser<RegexItem> by termWithAlternation
}