PHP Pagination from Huge JSON array_chunk in to multiple files and getting offset

So I have this huge file that has 45K+ arrays and I can’t just open a huge file on live server with high traffic from every request so I used array_chunk($array, 1000) and saved them in 46 files.

Now I want to read those files when specific page is accessed.

Problem?

$offset seems to be working fine with some pages but mostly offset changes to - number (minus number). Checked page 25, 50, 75 and more…

My Math is kinda (Very) weak, so any help will be appreciated. Thanks!

<?php
    $page = ! empty( $_GET['page'] ) ? (int) $_GET['page'] : 1;
    $limt = 40;  //Page array/item limit
    $fcnt = 46; //Total number of files
    $tarr = 45187; //Total number of arrays
    $fmu0 = (int)($limt*$fcnt*$page/$tarr); //Getting the file number according to page number
    if(file_exists("$fmu0.json")){
    $id = json_decode(file_get_contents("$fmu0.json"),true); 

    //Each file has 1000 arrays except the last file which has 187 arrays

    $tpgs = ceil($tarr/$limt); //Total number of pages
    $mult = $fmu0*count($id);
    $offset = ($page - 1) * $limt-$mult;
    if( $offset < 0 ){$offset = 0;}
    $id = array_slice( $id, $offset, $limt );
    var_dump($id);
    }
?>

Answer

1000 objects per file and 40 objects per page makes 25 pages per file.

Here’s how to find the file containing objects for $page number:

$fmu0 = floor($page / 25);

And here’s how to find the starting index of the group of 40 ($limt) objects within that file corresponding to $page number, when the first page is 1:

$offset = (($page - 1) * $limt) - ($fmu0 * 1000);

---

<?php

$page = (!empty($_GET['page']) && 0 < $_GET['page'])
    ? (int)$_GET['page']: 1;

$limt = 40;  //Page array/item limit

// FIND FILE, 25 pages per file
$fmu0 = floor($page / 25);

if(file_exists("$fmu0.json")){
    $id = json_decode(file_get_contents("$fmu0.json"),true);     

    // FIND GROUP of 40 ($limt) page objects, 1000 objects per file
    $offset = (($page - 1) * $limt) - ($fmu0 * 1000);

    $id = array_slice( $id, $offset, $limt );
    var_dump($id);

}
?>