<?php
// Simple response (errors, and anything but a successful poll response).
// Not a web page to display, but a message for the client javascript,
// which it will most likely discard.  Errors will be sent with an HTTP
// error code, which is the main thing the javascript will want to know.
function resp($msg, $code=0)
{
        if($code) header("HTTP/1.1 $code $msg");
        header('Content-Type: text/plain');
        echo $msg;
        exit;
}

// See if we're updating or reading to set db open mode.
if($_REQUEST['POLL']) $mode = 'r';
else if($_REQUEST['ADD']) $mode = 'w';
else resp('Missing request',400);

// If we're writing, we need to have a handle.
if($mode == 'w' && !$_REQUEST['NAME']) resp('Missing name', 400);

// Open the DB, and declare an error if it fails.  
$dbloc = '/var/wwwwrite/bennet/chatstat';
$db = dba_open($dbloc, $mode, "db4");
if(!$db) resp('Unable to open database',500);

// Get the message head number.
$head = (int)dba_fetch('nextmsg', $db);

// Take care of a write.
if($mode == 'w') {
        if(!dba_replace("msg_$head", $_REQUEST['ADD'], $db) ||
           !dba_replace("id_$head", $_REQUEST['NAME'], $db))
                resp('DB write failed', 500);
        ++$head;
        if(!dba_replace("nextmsg", "$head", $db)) resp('DB write failed', 500);

	    // Remove an old message if there are enough.  Prevent the database
        // from growing unboundedly.
	    $tail = $head - 50;
        if($tail >=1) {
                // We don't respond with error for this failure, since it's not
                // a user problem.  
                dba_delete("msg_$tail", $db);
                dba_delete("id_$tail", $db);
        }
        resp("OK");
}

// Build a response.  Collect the messages starting with POLL through the
// latest, but not more than 5 messages (dropping earlier ones).
$messages = array();
$ids = array();
$start = max(1, $head-10, $_REQUEST['POLL']);
for($i = $start; $i < $head; ++$i) {
        $d = dba_fetch("msg_$i", $db);
        if($d === FALSE) resp("DB read failed", 500);
        $messages[] = $d;
        $d = dba_fetch("id_$i", $db);
        if($d === FALSE) resp("DB read failed", 500);
        $ids[] = $d;
}
$result = array('head' => $head, 'messages' => $messages, 'ids' => $ids);

// Return the response encoded as json.
header('Content-Type: application/json');
echo json_encode($result);