Sentence Extractor

<!--Write a PHP program SentenceExtractor.php that takes a text from a textarea and a word from an input field
and prints all sentences from the text, containing that word. A sentence is any sequence of words ending
with ., ! or ?.-->

<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title>Sentence Extractor</title>
    <style type="text/css">
        #container {
            width: 340px;
        }

        input[type="text"] {
            width: 200px;
            text-indent: 2px;
        }
    </style>
</head>
<body>
<div id="container">
    <form method="post">
        <p><textarea name="text" cols="50" rows="8" placeholder="Enter your text..."
                     autofocus required></textarea></p>

        <p><label for="word">Enter word to check:</label>
            <input type="text" name="word" id="word" required/></p>
        <input type="submit" value="Extract sentence"/>
    </form>
    <p>
        <?php
        mb_internal_encoding('UTF-8');

        if (!isset($_POST['text']) || !isset($_POST['word']) ||
            trim($_POST['text']) === '' || trim($_POST['word']) === ''
        ) {
            die('Please, enter text in Each Textfield on Input Form!!!');
        }

        $text = trim($_POST['text']);
        $contained_word = trim($_POST['word']);
        $word_length = strlen($contained_word);
        $text_words = str_word_count($text, 2);
        if (in_array($contained_word, $text_words)) {
            $start_index = 0;
            foreach ($text_words as $word_position => $word) {
                if ($word === $contained_word) {
                    $dot_index = stripos($text, '.', ($word_position + $word_length));
                    $exclamation_index = stripos($text, '!', ($word_position + $word_length));
                    $question_index = stripos($text, '?', ($word_position + $word_length));
                    if ($dot_index === false && $exclamation_index === false && $question_index === false) {
                        break;
                    }

                    $end_sentence = strlen($text) + 1;
                    if ($dot_index !== false && $dot_index < $end_sentence) {
                        $end_sentence = $dot_index;
                    }
                    if ($exclamation_index !== false && $exclamation_index < $end_sentence) {
                        $end_sentence = $exclamation_index;
                    }
                    if ($question_index !== false && $question_index < $end_sentence) {
                        $end_sentence = $question_index;
                    }

                    if ($end_sentence > $word_position) {
                        echo substr($text, $start_index, ($end_sentence - $start_index + 1)) . ' ';
                    }

                    $start_index = $end_sentence + 1;
                }
            }
        }
        ?>
    </p>
</div>
</body>
</html>