lexer.cpp

#include "lexer.h"

Lexer::Lexer(const string & input) {
	this->input = input;
	this->index = 0;
}

Token Lexer::getNextToken() {
    while (index < input.size() && isspace(input[index])) index++;

    if (index >= input.size()) return (Token){END, ""};

    if (isalpha(input[index])) {
        string buffer;
        while (index < input.size() && (isalnum(input[index]) || input[index] == '_')) {
            buffer += input[index++];
        }
        if (buffer == "CREATE") return (Token){CREATE, buffer};
        if (buffer == "TABLE") return (Token){TABLE, buffer};
        if (buffer == "INSERT") return (Token){INSERT, buffer};
        if (buffer == "INTO") return (Token){INTO, buffer};
        if (buffer == "VALUES") return (Token){VALUES, buffer};
        if (buffer == "SELECT") return (Token){SELECT, buffer};
        if (buffer == "FROM") return (Token){FROM, buffer};
        if (buffer == "WHERE") return (Token){WHERE, buffer};
        if (buffer == "INTEGER") return (Token){INTEGER, buffer};
        if (buffer == "VARCHAR") return (Token){VARCHAR, buffer};
        if (buffer == "DATE") return (Token){DATE, buffer};
        return (Token){IDENTIFIER, buffer};
    }

    if (isdigit(input[index])) {
        string buffer;
        while (index < input.size() && isdigit(input[index])) {
            buffer += input[index++];
        }
        return (Token){NUMBER, buffer};
    }

    if (input[index] == '\'') {
        ++index; // Skip opening quote
        string buffer;
        while (index < input.size() && input[index] != '\'') {
            buffer += input[index++];
        }
        if (index < input.size() && input[index] == '\'') ++index; // Skip closing quote
        return (Token){STRING, buffer};
    }

    switch (input[index++]) {
        case '*': return (Token){STAR, "*"};
        case ',': return (Token){COMMA, ","};
        case '(': return (Token){LPAREN, "("};
        case ')': return (Token){RPAREN, ")"};
        case ';': return (Token){SEMICOLON, ";"};
        case '=': return (Token){EQUALS, "="};
        case '<':
            if (input[index] == '=') { ++index; return (Token){LESS_EQUALS, "<="}; }
            return (Token){LESS, "<"};
        case '>':
            if (input[index] == '=') { ++index; return (Token){GREATER_EQUALS, ">="}; }
            return (Token){GREATER, ">"};
        case '!':
            if (input[index] == '=') { ++index; return (Token){NOT_EQUALS, "!="}; }
            break;
    }

    return (Token){ERROR, string(1, input[index - 1])};
}