PHP - MYSQL JSON TEXT FILE

<?php

// Initialize variable for database credentials
$dbhost = 'localhost';
$dbuser = 'root';
$dbpass = '';
$dbname = 'history';

//Create database connection
  $dblink = new mysqli($dbhost, $dbuser, $dbpass, $dbname);

//Check connection was successful
  if ($dblink->connect_errno) {
     printf("Failed to connect to database");
     exit();
  }

//Fetch 3 rows from actor table

  $result = $dblink->query("SELECT * FROM main");

//Initialize array variable
  $dbdata = array();

//Fetch into associative array
  while ( $row = $result->fetch_assoc())  {

  $row = array_map('utf8_encode', $row); //conversione per caratteri speciali èùòà
  $dbdata[]=$row;

  //debug_zval_dump($dbdata);
  }

//Print array in JSON format
 //echo json_encode($dbdata);



 //echo "<pre>";
 //echo json_encode($dbdata, JSON_PRETTY_PRINT);
 //echo "</pre>";



 $myFile = "js_history_test.json";
 $fh = fopen($myFile, 'w') or die("can't open file");
 $stringData = json_encode($dbdata);
 fwrite($fh, $stringData);
 fclose($fh);


//START FILE
 $prepend = "
 [
    {
        \"id\":\"js_history\",
        \"title\":\"ROMAN EMPIRE\",
        \"description\":\"<p>descrizione</p>\",
        \"focus_date\":\"-753-01-01 12:00:00\",
        \"initial_zoom\":\"39\",
        \"image_lane_height\":50,
        \"events\":
  ";

$file = 'js_history_test.json';

$fileContents = file_get_contents($file);
echo $fileContents;




//MIDDLE FILE
file_put_contents($file, $prepend . $fileContents);



//END FILE
$myfile = fopen("js_history_test.json", "a") or die("Unable to open file!");
$txt = "}]";
fwrite($myfile, "\n". $txt);
fclose($myfile);



 ?>