query("tanks", "SELECT * FROM tanks WHERE record_id = 1 LIMIT 1");
$tank = $tank_res->fetch_assoc();
// Default time window
$defaultEnd = date('Y-m-d\TH:i', strtotime('+2 hours')); // now formatted for input
$defaultStart = date('Y-m-d\TH:i');
// Handle GET parameters if set
$startDate = $_GET['start_date'] ?? $defaultStart;
$endDate = $_GET['end_date'] ?? $defaultEnd;
$xData = [];
$yData = [];
$current = strtotime($endDate);
$start = strtotime($startDate);
$prev_liters = 0;
while ($current >= $start) {
$next = $current - (5 * 60); // 5 min earlier
$startStr = date('Y-m-d H:i:s', $current);
$endStr = date('Y-m-d H:i:s', $next);
$res = $db->query(
"tank_level_log",
"SELECT AVG(distance) AS avg_distance
FROM tank_level_log
WHERE date_time_measured BETWEEN '$endStr' AND '$startStr'"
);
$avgDist = 0;
if ($res && $res->num_rows > 0) {
$row = $res->fetch_assoc();
$avgDist = $row['avg_distance'];
}
if (!is_numeric($avgDist)) {
$avgDist = 0;
}
// Convert to liters
$converted = $functions->calculate_horizontal_cylinder_volume(
$tank['radius_mm'],
($tank['radius_mm'] * 2) - ($avgDist - 1),
$tank['length_mm']
);
$val = floatval($converted['fluid_volume_liters']);
if (!is_finite($val))
$val = 0;
// Append values
$yData[] = $val - $prev_liters;
$prev_liters = $val;
$xData[] = date('Y-m-d H:i:s', $current);
// Move to next step
$current = $next;
}
?>