Highlighting text with str_ireplace() - php

Question

I have an interesting problem where I am highlighting text from a keyword array using PHP's str_ireplace().
Let's say this is my array of keywords or phrases that I want to highlight from a sample text:
$keywords = array('eggs', 'green eggs');
And this is my sample text:
$text = 'Green eggs and ham.';
Here is how I am highlighting the text:
$counter = 0;
foreach ($keywords as $keyword) {
$text = str_ireplace($keyword, '<span class="highlight_'.($counter%5).'">'.$keyword.'</span>', $text);
$counter++;
}
The problem with this is that green eggs will never get a match because eggs has already been replaced in the text as:
Green <span class="highlight_0">eggs</span> and ham.
There may also be cases where there is partial overlaps such as:
$keywords = array('green eggs', 'eggs and');
What is a smart way to tackle this sort of issue?

Answer 1

Reverse the order:
$keywords = array('green eggs', 'eggs');
The simplest way is to do the longest strings first and move on to shorter ones after. Just make sure you don't double-over the same string (if it matters).

Answer 2

Maybe this is not the prettiest solution, but you could track the locations where your keywords occur, and then find where they overlap and adjust where you want to include the span tags
$keywords = array('eggs', 'n eggs a', 'eggs and','green eg');
$text = 'Green eggs and ham.';
$counter = 0;
$idx_array = array();
$idx_array_last = array();
foreach ($keywords as $keyword) {
$idx_array_first[$counter] = stripos($text, $keyword);
$idx_array_last[$counter] = $idx_array_first[$counter] + strlen($keyword);
$counter++;
}
//combine the overlapping indices
for ($i=0; $i<$counter; $i++) {
for ($j=$counter-1; $j>=$i+1; $j--) {
if (($idx_array_first[$i] <= $idx_array_first[$j] && $idx_array_first[$j] <= $idx_array_last[$i])
|| ($idx_array_last[$i] >= $idx_array_last[$j] && $idx_array_first[$i] <= $idx_array_last[$j])
|| ($idx_array_first[$j] <= $idx_array_first[$i] && $idx_array_last[$i] <= $idx_array_last[$j])) {
$idx_array_first[$i] = min($idx_array_first[$i],$idx_array_first[$j]);
$idx_array_last[$i] = max($idx_array_last[$i],$idx_array_last[$j]);
$counter--;
unset($idx_array_first[$j],$idx_array_last[$j]);
}
}
}
array_multisort($idx_array_first,$idx_array_last); //sort so that span tags are inserted at last indices first
for ($i=$counter-1; $i>=0; $i--) {
//add span tags at locations of indices
$textnew = substr($text,0,$idx_array_first[$i]).'<span class="highlight_'.$i.'">';
$textnew .=substr($text,$idx_array_first[$i],$idx_array_first[$i]+$idx_array_last[$i]);
$textnew .='</span>'.substr($text,$idx_array_last[$i]);
$text = $textnew;
}
Output is
<span class="highlight_0">Green eggs and</span> ham.