// swap(0,1,'the')=hte
function swap($posa,$posb,$word){
    $a = $word{$posa};
    $b = $word{$posb};
    $word{$posa} = $b;
    $word{$posb} = $a;
    return $word;
}
//condense('coffee',2)=cofee
function condense($word,$pos){
    $len = strlen($word);
    for($a=0;$a<$len;$a++){
        if($a==$pos){ $a++; } // skip ahead one..
        $ret .= $word{$a};
    }
    return $ret;
}

/** * Trims an array from empty elements.
 *
 * @param $a the array to trim.
 * @return a new array with the empty
elements removed.
 */

function array_trim($a) {
$j = 0;
for ($i = 0; $i < count($a);$i++) {
        if ($a[$i] != "")
        {
                $b[$j++] = $a[$i];
        }
}

return $b;
}


/* note that the algorithm in the following function was written by the generous joeldg on
        http://lucifer.intercosmos.net/?view=SNIP&item=115 which is where i found it    */

function generateTypos ($word, $depth=4) {
        // depth defines just how far to go with generating typos..
        //$depth = 4;

## Physical errors
// all keyboard specific typos based on QWERTY keyboards
// letters near keyboard edge and corners have fewer
// letters in order of most commonly used within english language

# center    sdfghjk
# top        wertyuio
# bottom    xcvbn
# corners    qpzm
# left        qaz
# right        plm
/*
created with : $freq = explode(" ", $lfreq);
while(list($key,$val)=each($common)){ reset($freq); echo "$"."common['".$key."'] = array(";
    for($a=0;$a<count($freq);$a++){ if(in_array($freq[$a], $val)){ echo "'".$freq[$a]."',"; } }
    echo ");\n"; }
*/
$common['a'] = array('s','z','q');
$common['b'] = array('n','g','v');
$common['c'] = array('d','v','x');
$common['d'] = array('e','s','c','f');
$common['f'] = array('r','t','c','d','g','b');
$common['g'] = array('r','n','t','h','b','f');
$common['h'] = array('n','t','g','b','y','j');
$common['i'] = array('o','u','k');
$common['j'] = array('i','n','u','m','h','k');
$common['k'] = array('i','o','l','m','j');
$common['l'] = array('p','m','k');
$common['m'] = array('n','k','j');
$common['n'] = array('m','h','b');
$common['o'] = array('i','l','p');
$common['p'] = array('o','l');
$common['q'] = array('a','w');
$common['r'] = array('e','t','g','f');
$common['s'] = array('e','a','d','w','x');
$common['t'] = array('r','g','y');
$common['u'] = array('i','y','j');
$common['v'] = array('c','b','f');
$common['w'] = array('e','s','q');
$common['x'] = array('s','c','z');
$common['y'] = array('t','u','h');
$common['z'] = array('s','a','x');

# from
# http://deafandblind.com/word_frequency.htm
# $lfreq = "e t a o i n s r h l d c u m f p g w y b v k x j q z"; // standard
$lfreq = explode(" ", "e i s a r n t o l c d u g p m h b y f v k w z x j q"); // based on 45k words

$firstletter = explode(" ", "t o a w b c d s f m r h i y e g l n o u j k");
$secondletter = explode(" ", "h o e i a u n r t");
$lastletter = explode(" ", "e s t d n r y f l o g h a k m p u w");

$dualletter = explode(" ", "th he an in er on re ed nd ha at en es of nt ea ti to io le is ou ar as de rt ve");
$doubleletter = explode(" ", "ss ee tt ff ll mm oo");


if($word){
    $wlen = strlen($word);
    for($a=0;$a<$wlen;$a++){
        $w[] = $word{$a};
        if(!($a+1 >= $wlen)){
            $w2[$a] = $word{$a}.$word{$a+1};
        }
    }

    ############## most common typos ##############
    // first dual letters..
    while(list($key,$val)=each($dualletter)){
        if(in_array($val, $w2)){
            $arrval = array_search ($val, $w2);
            $typos[] = swap($arrval, $arrval+1, $word);
        }
    }

    // second double letters.
    while(list($key,$val)=each($doubleletter)){
        if(in_array($val, $w2)){
            $arrval = array_search ($val, $w2);
            $typos[] = condense($word, $arrval);
        }
    }
    ##############  ##############  ###############

    //now lets generate possible mechanical typos. silly fingers not finging..
    while(list($key,$val)=each($w)){
        $repls = $common[$val];
            $d=0;
            for($a=0;$a<count($repls);$a++){
                $tmp = $word;
                $tmp{$key} = $repls[$a];
                $typos[] = $tmp;
                $d++;
                if($d>=$depth){$a=100;} // breakout
            }
    }
}

return($typos);
}