PHP计数器重置,重定向,没有负值

I have this counter and everything is working great with it but i would like to modify it. I cant code shit and i dont understand code but im tryiing my best and google stuff and test stuff by myself.

So what do i need it to do? When 10 clicks are made a redirect is made to ''http://stackoverflow.com'' When 10 clicks are made the counter restarts. The value cant reach negative like -1 -2 -3 etc. If i click and close the site it counts it like -1 click or simplier sed it removes my click.

The code.

index.php

<meta http-equiv="Refresh" content="60">

<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1, minimum-scale=1" />

<title>AJAX &amp; PHP Click-Counter with Flat File Storage (text file)</title>
<!-- http://blog.fofwebdesign.co.uk/23-click-counter-with-flat-file-storage-text-file-ajax-php -->

<style>
html, body { margin:0; padding:0; font:16px/1.75 Verdana, Arial, Helvetica, sans-serif }
.page-content { padding:1em; max-width:64em; margin:auto }

.click-count { color:green; font-weight:bold }
</style>

</head>
<body>

<div class="page-content">


<?php 

$clickcount = explode("
", file_get_contents('counter.txt'));
foreach($clickcount as $line){
    $tmp = explode('||', $line);
    $count[trim($tmp[0])] = trim($tmp[1]);
    }

?>

<center><b class="click-trigger" data-click-id="click-001">+1 click me</b> | <b class="click-trigger2" data-click-id="click-001">-1 click me</b>
| Clicked <span id="click-001" class="click-count"><?php echo $count['click-001'];?></span> times.</center>


<script>
var clicks = document.querySelectorAll('.click-trigger'); // IE8
for(var i = 0; i < clicks.length; i++){
    clicks[i].onclick = function(){
        var id = this.getAttribute('data-click-id');
        var post = 'id='+id; // post string
        var req = new XMLHttpRequest();
        req.open('POST', 'counter.php', true);
        req.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
        req.onreadystatechange = function(){
            if (req.readyState != 4 || req.status != 200) return; 
            document.getElementById(id).innerHTML = req.responseText;
            };
        req.send(post);
        }
    }
</script>

<script>
var clicks = document.querySelectorAll('.click-trigger2'); // IE8
for(var i = 0; i < clicks.length; i++){
    clicks[i].onclick = function(){
        var id = this.getAttribute('data-click-id');
        var post = 'id='+id; // post string
        var req = new XMLHttpRequest();
        req.open('POST', 'counter2.php', true);
        req.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
        req.onreadystatechange = function(){
            if (req.readyState != 4 || req.status != 200) return; 
            document.getElementById(id).innerHTML = req.responseText;
            };
        req.send(post);
        }
    }
</script>

</body>
</html>

counter.php (counts only +1 +1 +1 etc)

<?php 

/* Notes - add items manually to 'counter.txt'
           one item per line, in this format;
           id||0
           e.g. click-005||0
           e.g. my-id||0
           e.g. download-01||0
*/

$file = 'counter.txt'; // path to text file that stores counts
$fh = fopen($file, 'r+');
$id = $_REQUEST['id']; // posted from page
$lines = '';
while(!feof($fh)){
    $line = explode('||', fgets($fh));
    $item = trim($line[0]);
    $num = trim($line[1]);
    if(!empty($item)){
        if($item == $id){
            $num++; // increment count by 1
            echo $num;
            }
        $lines .= "$item||$num
";
        }
    } 
file_put_contents($file, $lines);
fclose($fh);

?>   

counter2.php ( counts - clicks like -1 -2 -3 etc)

<?php 

/* Notes - add items manually to 'counter.txt'
           one item per line, in this format;
           id||0
           e.g. click-005||0
           e.g. my-id||0
           e.g. download-01||0
*/

$file = 'counter.txt'; // path to text file that stores counts
$fh = fopen($file, 'r+');
$id = $_REQUEST['id']; // posted from page
$lines = '';
while(!feof($fh)){
    $line = explode('||', fgets($fh));
    $item = trim($line[0]);
    $num = trim($line[1]);
    if(!empty($item)){
        if($item == $id){
            $num--; // increment count by 1
            echo $num;
            }
        $lines .= "$item||$num
";
        }
    } 
file_put_contents($file, $lines);
fclose($fh);

?>   

counter.txt ( stores the clicks )

click-001||0
click-002||0
click-003||0

</div>