Replace (add) words case sensitive from arrays - php

Question

I am new to php and especially to regex.
My target is to enrich textes automatically with hints for "keywords" which are listed in arrays.
So far I had come.
$pattern = array("/\bexplanations\b/i",
"/\btarget\b/i",
"/\bhints\b/i",
"/\bhint\b/i",
);
$replacement = array("explanations <i>(Erklärungen)</i>",
"target <i>Ziel</i>",
"hints <i>Hinsweise</i>",
"hint <i>Hinweis</i>",
);
$string = "Target is to add some explanations (hints) from an array to
this text. I am thankful for every hint.";
echo preg_replace($pattern, $replacement, $string);
returns:
target <i>Ziel</i> is to add some explanations <i>(Erklärungen)</i> (hints <i>Hinsweise</i>) from an array to this text. I am thankful for every hint <i>Hinweis</i>
1) In generally I wonder if there are more elegant solutions (eventually without replacing the original word)?
On later state the arrays will contain more than 1000 items... and come from mariadb.
2) How can I achive, that the word "Targets" achives a case sensitive treatment?
(without duplicate the length of my arrays).
Sorry for my English and many thanks in advance.

Answer 1

If you project to increase the size of your array and if the text may be a bit long, processing all the text (once per word) isn't a reliable way. Also, with a large array, it isn't reliable to build a giant alternation with all the words.
But if you store all the translations in an associative array and split the text on word-boundaries, you can do it in one pass:
// Translation array with all keys lowercase
$trans = [ 'explanations' => 'Erklärungen',
'target' => 'Ziel',
'hints' => 'Hinsweise',
'hint' => 'Hinweis'
];
$parts = preg_split('~\b~', $text);
$partsLength = count($parts);
// All words are in the odd indexes
for ($i=1; $i<$partsLength; $i+=2) {
$lcWord = strtolower($parts[$i]);
if (isset($trans[$lcWord]))
$parts[$i] .= ' <i>(' . $trans[$lcWord] . ')</i>';
}
$result = implode('', $parts);
Actually the limitation here is that you can't use a key that contains a word-boundary (if you want to translate a whole expression with several words for instance), but if you want to handle this case, you can use preg_match_all in place of preg_split and build a pattern that tests these special cases before, something like:
preg_match_all('~mushroom pie\b|\w+|\W*~iS', $text, $m);
$parts = &$m[0];
$partsLength = count($parts);
$i = 1 ^ preg_match('~^\w~', $parts[0]);
for (; $i<$partsLength; $i+=2) {
...
(if you have a lot of exceptions (too many) other strategies are possible.)

Answer 2

Enclose search words with parentheses in regex patterns and use backteferences in replacements. 
See this PHP demo:
$pattern = array("/\b(explanations)\b/i", "/\b(target)\b/i", "/\b(hints)\b/i", "/\b(hint)\b/i", );
$replacement = array('$1 <i>(Erklärungen)</i>', '$1 <i>Ziel</i>', '$1 <i>Hinsweise</i>', '$1 <i>Hinweis</i>', );
$string = "Target is to add some explanations (hints) from an array to this text. I am thankful for every hint.";
echo preg_replace($pattern, $replacement, $string);
That way, you will replace with the words found with actual case used in the text.
Note it is very important to make sure the patterns go in the descending order with longer patterns coming before shorter ones (first Targets, then Target, etc.)