<?php

/**
 * Разбирвет строку запроса на токены
 */
class Lexer
{
    const TOKEN_NOT    = 1;
    const TOKEN_OR     = 2;
    const TOKEN_LPAREN = 3;
    const TOKEN_RPAREN = 4;
    const TOKEN_AND    = 5;
    const TOKEN_WORD   = 6;
    const TOKEN_EOL    = 7;

    protected $src;
    private   $offset = 0;
    public    $token;

    public function __construct ()
    {
    }

    function setSource ($src)
    {
        $this->src = $src;
        $this->offset;
    }

    private function skipSpace ()
    {
        while (!$this->isEOL() && $this->getChar() == " ") { 
            $this->offset++; 
        }
    }

    private function getChar ()
    {
        return $this->src [$this->offset]; 
    }
    
    /**
     * Проверяет на конец строки
     */
    private function isEOL () {
        return $this->offset >= strlen($this->src);
    }

    /**
     * Односимвольный токен
     */
    private function easyToken () {
        $ch = $this->getChar ();
        switch ($ch) {
            case '~': $token = array(self::TOKEN_NOT, $ch); break;
            case '|': $token = array(self::TOKEN_OR, $ch); break;
            case '(': $token = array(self::TOKEN_LPAREN, $ch); break;
            case ')': $token = array(self::TOKEN_RPAREN, $ch); break; 
            case '&': $token = array(self::TOKEN_AND, $ch); break; 
            default:
                $this->offset++;
                $token = $this->getToken();
        }
        $this->offset++;
        return $token;
    } 

    /**
     * Возвращает следующий токен
     */
    public function getToken ()
    {
        $this->skipSpace ();
        if ($this->isEOL()) {
            return array(self::TOKEN_EOL, "");
        }
        if (ctype_alpha($this->getChar())) {
            $start = $this->offset;
            while (!$this->isEOL() && ctype_alpha($this->getChar())) {
                $this->offset ++;
            }
            return array(self::TOKEN_WORD, substr ($this->src, $start, $this->offset-$start));
        }
        return $this->easyToken();
    }

    public function nextToken ()
    {
        $this->token = $this->getToken();
    }    
}

?>