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 * Copyright (C) jparsec.org                                                *
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 * Licensed under the Apache License, Version 2.0 (the "License");           *
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package org.jparsec.examples.bnf.parser;

import java.util.List;

import org.jparsec.Parser;
import org.jparsec.Parsers;
import org.jparsec.Terminals;
import org.jparsec.examples.bnf.ast.AltRule;
import org.jparsec.examples.bnf.ast.LiteralRule;
import org.jparsec.examples.bnf.ast.Rule;
import org.jparsec.examples.bnf.ast.RuleDef;
import org.jparsec.examples.bnf.ast.RuleReference;
import org.jparsec.examples.bnf.ast.SequentialRule;

/**
 * Parser for bnf rules.
 * 
 * @author benyu
 */
public final class RuleParser {
  
  static final Parser LITERAL = Terminals.StringLiteral.PARSER.map(LiteralRule::new);
  
  static final Parser IDENT = Terminals.Identifier.PARSER.notFollowedBy(TerminalParser.term("::="))
      .map(RuleReference::new);
  
  static Parser RULE_DEF = Parsers.sequence(
      Terminals.Identifier.PARSER, TerminalParser.term("::="), rule(), (name, __, r) -> new RuleDef(name, r));
  
  public static Parser> RULE_DEFS = RULE_DEF.many();
  
  static Parser rule() {
    Parser.Reference ref = Parser.newReference();
    Parser atom = Parsers.or(LITERAL, IDENT, unit(ref.lazy()));
    Parser parser = alternative(sequential(atom));
    ref.set(parser);
    return parser;
  }

  static Parser unit(Parser rule) {
    return Parsers.or(
        rule.between(TerminalParser.term("("), TerminalParser.term(")")),
        rule.between(TerminalParser.INDENTATION.indent(), TerminalParser.INDENTATION.outdent()));
  }
  
  static Parser sequential(Parser rule) {
    return rule.many1().map(list -> list.size() == 1 ? list.get(0) : new SequentialRule(list));
  }

  static Parser alternative(Parser rule) {
    return rule.sepBy1(TerminalParser.term("|")).map(list -> list.size() == 1 ? list.get(0) : new AltRule(list));
  }
}