Untitled

<?php
    class Post {
      public $title;
      public $content;
      public $timestamp;
      public $tags;
    }

    function get_posts($limit) {
      // connect to database
      $host     = "localhost";
      $username = "weblog";
      $password = "deadcats";
      $database = "weblog";

      $db_conn = mysqli_connect($host,$username,$password,$database);
      if (!$db_conn) {
        echo "Error: Unable to connect to MySQL." . PHP_EOL;
        echo "Debugging errno: " . mysqli_connect_errno() . PHP_EOL;
        echo "Debugging error: " . mysqli_connect_error() . PHP_EOL;
        exit;
      }

      $tag_filter =  htmlspecialchars($_GET["tag"]);

      $posts = array();

      if (!empty($tag_filter)) {
        $postfix = "JOIN posts_tags ON posts.id = posts_tags.post_id JOIN tags ON tags.id = posts_tags.tag_id WHERE tags.name = \"{$tag_filter}\"";
      }

      $sql = "SELECT posts.id, posts.title, posts.content, posts.timestamp FROM posts " . $postfix . " ORDER BY posts.id DESC";
      $result = $db_conn->query($sql);

      if ($result->num_rows > 0) {
          while($row = $result->fetch_assoc()) {
            $post = new Post();

            $post->id         = $row["id"];
            $post->title      = $row["title"];
            $post->content    = $row["content"];
            $post->timestamp  = $row["timestamp"];

            $post->tags = array();
            $tags_sql = "SELECT tags.name FROM posts_tags
                        JOIN tags ON tags.id = posts_tags.tag_id
                        WHERE posts_tags.post_id = {$post->id}";

            $tags_result = $db_conn->query($tags_sql);
            while($tags_row = $tags_result->fetch_assoc()) {
              array_push($post->tags, $tags_row["name"]);
            }

            array_push($posts, $post);
          }
      }

      mysqli_close($db_conn);

      return $posts;
    }

    function print_post($post) {
      $tags = "";
      foreach ($post->tags as $tag) {
        $tags .= " <a href=\"index.php?tag=\"" . $tag . "\">$tag</a>";
      }

      $output =  "<div class=\"common_item\">
                    <div class=\"p_title\">{$post->title}</div>
                    <hr align=\"left\">
                    <p class=\"text\">{$post->content}</p>
                    <div class=\"post_description\">
                      <div class=\"left\">
                        <b>Tags:</b> {$tags}
                      </div>
                      <div class=\"right\">
                        Posted on {$post->timestamp}
                      </div>
                    </div>
                  </div>";

      echo $output;
    }
?>

<!doctype html>
<html>
<head>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8"/> <link rel="stylesheet alternative" type="text/css" href="dark.css" id="dark-style">
    <link rel="stylesheet" type="text/css" href="light.css" id="light-style">
    <script type="text/javascript" src="scheme.js"></script>
    <title>Weblog about web-technologies</title>
</head>

<body>
<div id="content">
    <div id="header">
        <h2><a href="index.php">Weblog about web-technologies</a></h2>
        <h3><p class="annotation">Lorem ipsum dolor sit amet</p></h3>
    </div>

<?php
    $posts = get_posts();

    foreach ($posts as $post) {
      print_post($post);
    }
?>

  </div>

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    <ul>
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    <div id="list_r">
    <ul>
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        <li><a href="https://www.w3.org/standards/techs/css#w3c_all">W3C.org</a></li>
    </ul>
    </div>

    <h3>Switch theme</h3>
    <div id="list_s">
    <ul>
        <li><a href="#" onclick="changeCSS('light', 0);">Light</a></li>
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