Cis/EC.Helper/RabbitFunc/Compiler/Parser.cs

using EC.Helper.RabbitFunc.Expressions;
using EC.Helper.RabbitFunc.Syntax;

namespace EC.Helper.RabbitFunc.Compiler;

internal class Parser
{
    private readonly Tokenizer tokenizer;
    private TokenWithSpan lookahead;
    private TokenWithSpan token;

    public Parser(Tokenizer tokenizer)
    {
        if (tokenizer == null)
            throw new ArgumentNullException(nameof(tokenizer));

        this.tokenizer = tokenizer;
        Initialize();
    }

    private void Initialize()
    {
        FetchLookahead();
    }

    private Token NextToken()
    {
        token = lookahead;
        FetchLookahead();
        return token.Token;
    }

    private Token PeekToken()
    {
        return this.lookahead.Token;
    }

    private void FetchLookahead()
    {
        lookahead = new TokenWithSpan(tokenizer.NextToken(), tokenizer.TokenSpan);
    }

    private bool PeekToken(TokenKind kind)
    {
        return PeekToken().Kind == kind;
    }

    private bool PeekToken(Token check)
    {
        return PeekToken() == check;
    }

    private bool MaybeEat(TokenKind kind)
    {
        if (PeekToken().Kind == kind)
        {
            NextToken();
            return true;
        }
        return false;
    }

    private LambdaExpression ParseStatement()
    {
        while (true)
        {
            switch (PeekToken().Kind)
            {
                case TokenKind.Comment:
                case TokenKind.NewLine:
                    NextToken();
                    continue;
                case TokenKind.EndOfFile:
                    return null;

                default:
                    return ParseLambdaExpression();
            }
        }
    }

    private ExpressionType GetBinaryOperator(TokenKind kind)
    {
        return kind switch
        {
            TokenKind.Add => ExpressionType.Add,
            TokenKind.Subtract => ExpressionType.Subtract,
            TokenKind.Multiply => ExpressionType.Multiply,
            TokenKind.Divide => ExpressionType.Divide,
            TokenKind.Mod => ExpressionType.Modulo,
            TokenKind.Power => ExpressionType.Power,
            TokenKind.LessThan => ExpressionType.LessThan,
            TokenKind.LessThanOrEqual => ExpressionType.LessThanOrEqual,
            TokenKind.Equal => ExpressionType.Equal,
            TokenKind.GreaterThanOrEqual => ExpressionType.GreaterThanOrEqual,
            TokenKind.GreaterThan => ExpressionType.GreaterThan,
            TokenKind.NotEqual => ExpressionType.NotEqual,
            _ => throw new CompilerException(tokenizer.Position, string.Format("operator TokenKind:{0} error!", kind.ToString())),
        };
    }

    private IList<Expression> ParseArguments()
    {
        List<Expression> list = new List<Expression>();
        if (PeekToken().Kind != TokenKind.RightParen)
        {
            do
            {
                list.Add(ParseExpression());
            } while (MaybeEat(TokenKind.Comma));
        }

        return list;
    }

    private Expression ParseTerm()
    {
        Expression expr = null;
        Token token = NextToken();
        switch (token.Kind)
        {
            case TokenKind.Constant:
                expr = Expression.Constant(token.Value);
                break;

            case TokenKind.Subtract:
                expr = Expression.Negate(ParseExpression());
                break;

            case TokenKind.LeftParen:
                expr = ParseExpression();
                if (!MaybeEat(TokenKind.RightParen))
                    throw new CompilerException(tokenizer.Position, PeekToken().Text);
                break;

            case TokenKind.Identifier:
                switch (PeekToken().Kind)
                {
                    case TokenKind.LeftParen:
                        NextToken();
                        expr = Expression.Call(null, token.Text, ParseArguments());
                        if (!MaybeEat(TokenKind.RightParen))
                            throw new CompilerException(tokenizer.Position, PeekToken().Text);

                        break;

                    case TokenKind.Dot:
                        expr = Expression.Parameter(null, token.Text);
                        while (MaybeEat(TokenKind.Dot))
                        {
                            token = NextToken();
                            if (token.Kind != TokenKind.Identifier)
                                throw new CompilerException(tokenizer.Position, PeekToken().Text);
                            if (PeekToken().Kind == TokenKind.LeftParen)
                            {
                                expr = Expression.Call(expr, token.Text, ParseArguments());
                                if (!MaybeEat(TokenKind.RightParen))
                                    throw new CompilerException(tokenizer.Position, PeekToken().Text);
                                break;
                            }

                            expr = Expression.Member(expr, token.Text);
                        }
                        if (MaybeEat(TokenKind.LeftParen))
                        {
                            expr = Expression.Call(expr, token.Text, ParseArguments());
                            if (!MaybeEat(TokenKind.RightParen))
                                throw new CompilerException(tokenizer.Position, PeekToken().Text);
                        }
                        break;

                    default:
                        expr = Expression.Parameter(typeof(double), token.Text);
                        break;
                }
                break;

            case TokenKind.Not:
                return Expression.Not(ParseExpression());

            case TokenKind.IF:
                if (!MaybeEat(TokenKind.LeftParen))
                    throw new CompilerException(tokenizer.Position, PeekToken().Text);
                var test = ParseExpression();
                if (!MaybeEat(TokenKind.Comma))
                    throw new CompilerException(tokenizer.Position, PeekToken().Text);
                var trueExpre = ParseExpression();
                if (!MaybeEat(TokenKind.Comma))
                    throw new CompilerException(tokenizer.Position, PeekToken().Text);
                var falseExpre = ParseExpression();
                if (!MaybeEat(TokenKind.RightParen))
                    throw new CompilerException(tokenizer.Position, PeekToken().Text);

                expr = Expression.Condition(test, trueExpre, falseExpre);
                break;
        }

        return expr;
    }

    private Expression ParseExpression(byte precedence = 0)
    {
        Expression leftOperand = ParseTerm();
        while (true)
        {
            Token token = PeekToken();
            if (token is OperatorToken operatorToken && operatorToken.Precedence >= precedence)
            {
                NextToken();
                Expression rightOperand = ParseExpression(checked((byte)(operatorToken.Precedence + 1)));
                ExpressionType @operator = GetBinaryOperator(token.Kind);
                leftOperand = new BinaryExpression(@operator, leftOperand, rightOperand);
                continue;
            }

            break;
        }

        return leftOperand;
    }

    private LambdaExpression ParseLambdaExpression()
    {
        Token token = NextToken();
        if (token.Kind != TokenKind.Identifier)
            throw new CompilerException(tokenizer.Position, token.Text);

        var name = token.Text;
        var parameters = new List<ParameterExpression>();
        if (MaybeEat(TokenKind.LeftParen))
        {
            if (!MaybeEat(TokenKind.RightParen))
            {
                do
                {
                    token = NextToken();
                    if (token.Kind != TokenKind.Identifier)
                        throw new CompilerException(tokenizer.Position, token.Text);

                    parameters.Add(Expression.Parameter(typeof(double), token.Text));
                } while (MaybeEat(TokenKind.Comma));

                if (!MaybeEat(TokenKind.RightParen))
                    throw new CompilerException(tokenizer.Position, token.Text);
            }
        }
        if (!MaybeEat(TokenKind.Assign))
            throw new CompilerException(tokenizer.Position, PeekToken().Text);

        Expression body = ParseExpression();
        return Expression.Lambda(name, body, parameters);
    }

    public LambdaExpression Parse()
    {
        return ParseStatement();
    }
}