Infection History / Prediction

// https://www.mdwestserve.com/coronavirus/graphs.php
global $today;
global $normal;
$today = array();
$normal = array();
$q = "SELECT distinct name_of_location FROM coronavirus_populations ";
$r = $core->query($q);
while($d = mysqli_fetch_array($r)){
    $today[$d[name_of_location]] = 0; // count
    $normal[$d[name_of_location]] = ''; // string
}

global $days_to_predict;
$days_to_predict = '7';
if(isset($_POST['days'])){
    $days_to_predict = $_POST['days'];
}

global $buffer;
$buffer = '.85';
if(isset($_POST['buffer'])){
    $buffer = $_POST['buffer'];
}
global $debug_in;
global $debug_out;

function total_count($county){
    global $core;
    $q = "SELECT number_of_people FROM coronavirus_populations where name_of_location = '$county' ";
    $r = $core->query($q);
    $d = mysqli_fetch_array($r);
    return $d['number_of_people'];
}
function rate_of_infection($county){
    global $core;
    $q = "SELECT rate_of_infection FROM coronavirus_populations where name_of_location = '$county' ";
    $r = $core->query($q);
    $d = mysqli_fetch_array($r);
    return $d['rate_of_infection'];
}
function show_on_graph($county){
    // if has cases = true else false
    global $core;
    $q = "SELECT * FROM `coronavirus` order by id desc limit 1";
    $r = $core->query($q);
    $d = mysqli_fetch_array($r);
    $key = $county.'COVID19Cases';
    $count = $d[$key];
    if ($count == 0){
        return 'false';
    }else{
        return 'true';
    }

}
function make_county($county){
        global $core;
        $return = '';
        $t = '0'; // days
        $dt= '1'; // change in days
        // history
        $q = "SELECT distinct just_date FROM `coronavirus` order by just_date asc";
    $r = $core->query($q);
    $count=0;
    global $today;
    while($d = mysqli_fetch_array($r)){
        $date = $d['just_date'];
        $q2 = "SELECT * FROM `coronavirus` where just_date = '$date' order by id desc";
        $r2 = $core->query($q2);
        $d2 = mysqli_fetch_array($r2);
        $key = $county.'COVID19Cases';
        $last_count = $count;
        $count = $d2[$key];
        $return .= '{ label: "'.$date.'", y: '.$count.' }, ';
        $today[$county] = $count;
    }
        // predictive
        $next = date('Y-m-d',strtotime($date)+86400);
        $return .= make_county_prediction($county,$next,$count,$dt);
        $return = rtrim(trim($return), ",");
    return $return;
}
function make_county_prediction($county,$start,$count,$dt){
    global $debug_in;
    global $debug_out;
    global $core;
    $return = '';
    $start = new DateTime ($start, new DateTimeZone ('UTC'));
    global $days_to_predict;
    $end = new DateTime (" +$days_to_predict days", new DateTimeZone ('UTC'));
    $interval = new DateInterval ('P1D');
    $range = new DatePeriod ($start, $interval, $end);
    $N = $count; // total cases
    $Nmax = total_count($county); // population
    $a = rate_of_infection($county); // percentage infection rate
    $day_buffer = 0;
    foreach ($range as $date) {
    $out = $date->format ('Y-m-d');
        $debug_in .= "<li>$out N:$N</li>";
        $Nold=$N;
        $N=$N+$a*(1-$N/$Nmax)*$N*$dt;
        $r=($N-$Nold)/$dt;
    if(empty($base)){
        // only set base once
        global $buffer;
        $base = ($N - $r)*$buffer;
        $debug_out .= "<li><b>BASE: $base</b></li>";
    }
    $r = $r + $base;
    $debug_out .= "<li>$out N:$N r:$r</li>";
        $return .= '{ label: "'.$out.'", y: '.$r.' }, ';
    global $today;
    global $normal;
    if (intval($today[$county]) > intval($r) && intval($r) != 0 && $normal[$county] == '' && $day_buffer > 14){
        $normal[$county] = "<p style='background-color:lightgreen; '>On $out $county went under ".$today[$county]." to $r</p>";
    }
    $day_buffer++;
    }
    return $return;
}