package ch.bfh.parser;

import ch.bfh.lexer.CalculatorLexer;
import ch.bfh.lexer.Token;

public class StatementParser extends Parser{

    String input;
    ExpressionParser parsedExpression;

    public void parseStatement(String input){
        this.input = input;
        cl = new CalculatorLexer();
        cl.initLexer(input);
        parsedExpression = null;
        parse();
    }

    @Override
    protected void parse() {
        Token token = cl.nextToken();
        String variableName = null;
        lastToken = null;
        loop:
        while (token != null && token.type != Token.EOL) {
            switch (token.type) {
                case Token.LET:
                    if (lastToken != null)
                        throw new ParserException("The keyword 'let' can only be placed at the beginning of an expression.");
                    break;
                case Token.EQU:
                    if (lastToken == null || lastToken.type != Token.LET || variableName == null)
                        throw new ParserException("The token '=' can only be placed in a variable declaration context (let var = Expression).");
                    break;
                case Token.END:
                    if (lastToken != null)
                        throw new ParserException("The keyword 'exit' can only be placed at the beginning of an expression.");
                    else
                        System.exit(0);
                case Token.ID:
                    if (lastToken != null && lastToken.type == Token.LET && variableName == null) { // we are defining a new variable
                        variableName = token.str;
                        token = cl.nextToken();
                        continue loop; // lastToken value will thus still be 'let' so that we could then parse the '=' token that is supposed to come next correctly.
                    }else if (variableName != null && lastToken != null && lastToken.type != Token.EQU)
                        throw new ParserException("Two consecutive variables ('"+variableName+"' and '"+token.str+"') were found in the declaration context.");
                    // the expression started with a variable -> no definition -> meaning it is an expression
                default:
                    if (lastToken == null || lastToken.type == Token.EQU) {
                        parsedExpression = new ExpressionParser(cl, token, false);
                        if (lastToken != null && lastToken.type == Token.EQU) // this still need to be put in the variables list
                            variables.put(variableName, parsedExpression);
                    }else
                        throw new ParserException("Incomplete variable declaration. Expected: let var = Expression.");
                    break;
            }
            lastToken = token;
            token = cl.nextToken();
        }
        if (lastToken == null)
            return;
        if (lastToken.type == Token.LET || lastToken.type == Token.EQU)
            throw new ParserException("Incomplete variable declaration. Expected: let var = Expression.");
    }

    @Override
    public double getValue() {
        if (parsedExpression == null)
            throw new ParserException("Empty statement.");
        return parsedExpression.getValue();
    }
}