How to replace username with link in string? - php

Question

I'm trying to check posts to see whether they mention another user, by using #username. I want to replace that with a link to the user's profile.
This is what I've got... I haven't got any errors, but usernames just go through as text without the link. I feel like $getUsers/$gU isn't returning the results to $checkString, but I can't see anything wrong.
function post()
{
global $me;
if($_POST['message'])
{
$getUsers = mysql_query("SELECT user_id, user_name FROM users");
while($gU = mysql_fetch_array($getUsers))
{
$checkString = strpos($_POST['message'], "#".$gU['user_name']."");
if($checkString !== false)
{
$replaceFrom = "#".$gU['user_name']."";
$replaceTo = "<a href=\'/user.php?id=".$gU['user_id']."\'>".$gU['user_name']."</a>";
$checked = str_replace($replaceFrom, $replaceTo, $_POST['message']);
}
else
{
$checked = $_POST['message'];
}
}
mysql_query("INSERT INTO test_table VALUES ('', '".$me['user_id']."', '".$_POST['topic']."', '".$checked."', UNIX_TIMESTAMP())");
index();
}
else {
echo "
<form action='?action=insert' method='post'>
<input type=text name=topic maxlength=40>
<br><textarea name=message cols=80 rows=9></textarea>
<br><input type='submit' STYLE='color: black; background-color: white;' value='Submit' class='btn'>
</form>
";
}
}

Answer 1

mysql_query("INSERT INTO test_table VALUES ('', '".$me['user_id']."', '".$_POST['topic']."', '".$_POST['message']."', UNIX_TIMESTAMP())");
should be
mysql_query("INSERT INTO test_table VALUES ('', '".$me['user_id']."', '".$_POST['topic']."', '".$checked."', UNIX_TIMESTAMP())");
As your user table will eventually grow, I'd suggest compiling a set of potential usernames by searching for #(\w+), preparing a statement looking for that username, iterating through the results and replacing all instances for every returned row with the link.

Answer 2

I think you could have simplify your question by excluding the MySQL part. From what I understand you are trying to replace user mention with an HTML anchor tag.
Instead of looping through all the available users you can use preg_replace_callback() to check if any tagged user exists in system.
Please review the example code below. To simplify things I have created two functions. parseTag() will inject the HTML anchor link if the user exist, otherwise the original tag will be kept. getUserId() will return the user id it exists in the system instead:
<?php
function parseTag($tagInfo){
list($fullTag, $username) = $tagInfo;
$uid = getUserId($username);
if ($uid) {
return "<a href='/url/to/user/{$uid}'>{$fullTag}</a>";
}
return $fullTag;
}
function getUserId($username){
$userList = [null, 'john', 'mary'];
return array_search($username, $userList);
}
$comment = "Hello #john, #doe does not exists";
$htmlComment = preg_replace_callback("/#([\w]+)/", "parseTag", $comment);
echo $htmlComment;
Output:
Hello <a href='/url/to/user/1'>#john</a>, #doe does not exists