java-commons/muscript/src/main/java/io/gitlab/jfronny/muscript/compiler/Parser.java

package io.gitlab.jfronny.muscript.compiler;

import io.gitlab.jfronny.muscript.compiler.expr.*;

import java.util.*;

public class Parser {
    private final Lexer lexer;

    private final TokenData previous = new TokenData();
    private final TokenData current = new TokenData();

    public static Expr<?> parse(String source) {
        return new Parser(new Lexer(source)).parse();
    }

    public Parser(Lexer lexer) {
        this.lexer = lexer;
    }

    public Expr<?> parse() {
        advance();
        return expression();
    }

    // Expressions

    private Expr<?> expression() {
        try {
            return conditional();
        } catch (RuntimeException e) {
            if (e instanceof ParseException) throw e;
            else throw error(e.getMessage());
        }
    }

    private Expr<?> conditional() {
        Expr<?> expr = and();

        if (match(Token.QuestionMark)) {
            Expr<?> trueExpr = expression();
            consume(Token.Colon, "Expected ':' after first part of condition.");
            Expr<?> falseExpr = expression();
            expr = new Conditional(expr.asBoolExpr(), trueExpr, falseExpr);
        }

        return expr;
    }

    private Expr<?> and() {
        Expr<?> expr = or();

        while (match(Token.And)) {
            Expr<?> right = or();
            expr = new LogicBiExpr(expr.asBoolExpr(), right.asBoolExpr(), Token.And);
        }

        return expr;
    }

    private Expr<?> or() {
        Expr<?> expr = equality();

        while (match(Token.Or)) {
            Expr<?> right = equality();
            expr = new LogicBiExpr(expr.asBoolExpr(), right.asBoolExpr(), Token.Or);
        }

        return expr;
    }

    private Expr<?> equality() {
        Expr<?> expr = concat();

        while (match(Token.EqualEqual, Token.BangEqual)) {
            Token op = previous.token;
            Expr<?> right = concat();
            Expr.BoolExpr e = new Equal(expr, right);
            if (op == Token.BangEqual) e = new Not(e);
            expr = e;
        }

        return expr;
    }

    private Expr<?> concat() {
        Expr<?> expr = comparison();

        while (match(Token.Concat)) {
            Token op = previous.token;
            Expr<?> right = comparison();
            expr = new Concatenate(expr.asStringExpr(), right.asStringExpr());
        }

        return expr;
    }

    private Expr<?> comparison() {
        Expr<?> expr = term();

        while (match(Token.Greater, Token.GreaterEqual, Token.Less, Token.LessEqual)) {
            Token op = previous.token;
            Expr<?> right = term();
            expr = new Compare(expr.asNumberExpr(), right.asNumberExpr(), op);
        }

        return expr;
    }

    private Expr<?> term() {
        Expr<?> expr = factor();

        while (match(Token.Plus, Token.Minus)) {
            Token op = previous.token;
            Expr<?> right = factor();
            expr = new MathBiExpr(expr.asNumberExpr(), right.asNumberExpr(), op);
        }

        return expr;
    }

    private Expr<?> factor() {
        Expr<?> expr = exp();

        while (match(Token.Star, Token.Slash, Token.Percentage, Token.UpArrow)) {
            Token op = previous.token;
            Expr<?> right = exp();
            expr = new MathBiExpr(expr.asNumberExpr(), right.asNumberExpr(), op);
        }

        return expr;
    }

    private Expr<?> exp() {
        Expr<?> expr = unary();

        while (match(Token.UpArrow)) {
            Token op = previous.token;
            Expr<?> right = unary();
            expr = new MathBiExpr(expr.asNumberExpr(), right.asNumberExpr(), op);
        }

        return expr;
    }

    private Expr<?> unary() {
        if (match(Token.Bang, Token.Minus)) {
            Token op = previous.token;
            Expr<?> right = unary();
            return op == Token.Bang ? new Not(right.asBoolExpr()) : new Invert(right.asNumberExpr());
        }

        return call();
    }

    private Expr<?> call() {
        Expr<?> expr = primary();

        while (true) {
            if (match(Token.LeftParen)) {
                expr = finishCall(expr);
            }
            else if (match(Token.Dot)) {
                TokenData name = consume(Token.Identifier, "Expected field name after '.'.");
                expr = new Get(expr.asDynamicExpr(), Expr.literal(name.lexeme));
            }
            else if (match(Token.LeftBracket)) {
                expr = new Get(expr.asDynamicExpr(), expression());
                consume(Token.RightBracket, "Expected closing bracket");
            }
            else {
                break;
            }
        }

        return expr;
    }

    private Expr<?> finishCall(Expr<?> callee) {
        List<Expr.DynamicExpr> args = new ArrayList<>(2);

        if (!check(Token.RightParen)) {
            do {
                args.add(expression().asDynamicExpr());
            } while (match(Token.Comma));
        }

        consume(Token.RightParen, "Expected ')' after function arguments.");
        return new Call(callee.asDynamicExpr(), args);
    }

    private Expr<?> primary() {
        if (match(Token.Null)) return Expr.literalNull();
        if (match(Token.String)) return Expr.literal(previous.lexeme);
        if (match(Token.True, Token.False)) return Expr.literal(previous.lexeme.equals("true"));
        if (match(Token.Number)) return Expr.literal(Double.parseDouble(previous.lexeme));
        if (match(Token.Identifier)) return new Variable(previous.lexeme);

        if (match(Token.LeftParen)) {
            Expr<?> expr = expression();
            consume(Token.RightParen, "Expected ')' after expression.");
            return new Group(expr);
        }

        throw error("Expected expression.");
    }

    // Helpers
    private ParseException error(String message) {
        return new ParseException(new Error(current.line, current.character, current.ch, message));
    }

    private TokenData consume(Token token, String message) {
        if (check(token)) return advance();
        throw error(message);
    }

    private boolean match(Token... tokens) {
        for (Token token : tokens) {
            if (check(token)) {
                advance();
                return true;
            }
        }

        return false;
    }

    private boolean check(Token token) {
        if (isAtEnd()) return false;
        return current.token == token;
    }

    private TokenData advance() {
        previous.set(current);

        lexer.next();
        current.set(lexer.token, lexer.lexeme, lexer.line, lexer.character, lexer.ch);

        if (current.token == Token.Error) {
            throw error(current.lexeme);
        }

        return previous;
    }

    private boolean isAtEnd() {
        return current.token == Token.EOF;
    }

    // Token data
    private static class TokenData {
        public Token token;
        public String lexeme;
        public int line, character;
        public char ch;

        public void set(Token token, String lexeme, int line, int character, char ch) {
            this.token = token;
            this.lexeme = lexeme;
            this.line = line;
            this.character = character;
            this.ch = ch;
        }

        public void set(TokenData data) {
            set(data.token, data.lexeme, data.line, data.character, data.ch);
        }

        @Override
        public String toString() {
            return String.format("%s '%s'", token, lexeme);
        }
    }

    // Parse Exception
    public static class ParseException extends RuntimeException {
        public final Error error;

        public ParseException(Error error) {
            super(error.toString());
            this.error = error;
        }
    }
}