<?php
// Enable error reporting for debugging
ini_set('display_errors', 1);
ini_set('display_startup_errors', 1);
error_reporting(E_ALL);

$cacheFile = __DIR__ . '/wind.json';
$cacheTime = 3600; // 1 hour

// Check if a cached file exists and is recent
if (file_exists($cacheFile) && (time() - filemtime($cacheFile)) < $cacheTime) {
    header('Content-Type: application/json');
    readfile($cacheFile);
    exit;
}

// --- Grid setup ---

$nx = 36; // Grid points in longitude (every 10 degrees)
$ny = 18; // Grid points in latitude (every 10 degrees)
$lo1 = -180;
$la1 = 90;
$dx = 10;
$dy = 10;

$uData = array_fill(0, $nx * $ny, 0);
$vData = array_fill(0, $nx * $ny, 0);

// --- Build coordinate arrays for batch API call ---

$lats = [];
$lons = [];
for ($j = 0; $j < $ny; $j++) {
    $lat = $la1 - $j * $dy;
    for ($i = 0; $i < $nx; $i++) {
        $lon = $lo1 + $i * $dx;
        // Ensure longitude is within -180 to 180 range for the API
        $lats[] = round($lat, 4);
        $lons[] = round($lon, 4);
    }
}

// --- Fetch data from Open-Meteo in a single call ---

// The API expects `hourly` and `current` parameters.
$url = "https://api.open-meteo.com/v1/forecast?latitude=" . implode(',', $lats) . "&longitude=" . implode(',', $lons) . "&current=wind_speed_10m,wind_direction_10m";

$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($ch, CURLOPT_FOLLOWLOCATION, 1);
curl_setopt($ch, CURLOPT_TIMEOUT, 20);
$response = curl_exec($ch);
curl_close($ch);

if ($response) {
    $results = json_decode($response, true);

    // The API returns an array of results, one for each coordinate pair
    if (is_array($results)) {
        foreach ($results as $index => $data) {
            if (isset($data['current'])) {
                $windspeed = $data['current']['wind_speed_10m'];
                $winddirection = $data['current']['wind_direction_10m'];

                // Convert to u and v components
                // Wind direction: the direction from which the wind is blowing (0° for North, 90° for East)
                // Angle for calculation needs to be where the wind is going
                $angle = ($winddirection + 180) * M_PI / 180;
                $u = $windspeed * cos($angle); // Eastward component
                $v = $windspeed * sin($angle); // Northward component

                // The index in the response corresponds to the index in our grid
                if (isset($uData[$index]) && isset($vData[$index])) {
                    $uData[$index] = $u;
                    $vData[$index] = $v;
                }
            }
        }
    }
}


// --- Format Data ---

$refTime = gmdate("Y-m-d\\TH:i:s.vZ");

$formattedData = [
    [
        "header" => [
            "nx" => $nx,
            "ny" => $ny,
            "lo1" => $lo1,
            "la1" => $la1,
            "dx" => $dx,
            "dy" => $dy,
            "parameterCategory" => 2,
            "parameterNumber" => 2,
            "forecastTime" => 0,
            "refTime" => $refTime,
        ],
        "data" => $uData
    ],
    [
        "header" => [
            "nx" => $nx,
            "ny" => $ny,
            "lo1" => $lo1,
            "la1" => $la1,
            "dx" => $dx,
            "dy" => $dy,
            "parameterCategory" => 2,
            "parameterNumber" => 3,
            "forecastTime" => 0,
            "refTime" => $refTime,
        ],
        "data" => $vData
    ]
];

$json_data = json_encode($formattedData);

// Cache the result
file_put_contents($cacheFile, $json_data);

header('Content-Type: application/json');
echo $json_data;

?>