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

require_once __DIR__ . '/../config.php';

header('Content-Type: application/json');
header('Access-Control-Allow-Origin: *');

$cacheFile = __DIR__ . '/../assets/cache/wind.json';
$cacheTime = 3600; // 1 hour in seconds

// Check if a valid cache file exists
if (file_exists($cacheFile) && (time() - filemtime($cacheFile)) < $cacheTime) {
    readfile($cacheFile);
    exit;
}

// --- Helper Functions ---

/**
 * Calculates the great-circle distance between two points on a sphere.
 * @param float $lat1 Latitude of point 1
 * @param float $lon1 Longitude of point 1
 * @param float $lat2 Latitude of point 2
 * @param float $lon2 Longitude of point 2
 * @return float Distance in kilometers
 */
function haversineDistance($lat1, $lon1, $lat2, $lon2) {
    $earthRadius = 6371; // km
    $dLat = deg2rad($lat2 - $lat1);
    $dLon = deg2rad($lon2 - $lon1);
    $a = sin($dLat / 2) * sin($dLat / 2) +
       cos(deg2rad($lat1)) * cos(deg2rad($lat2)) *
       sin($dLon / 2) * sin($dLon / 2);
    $c = 2 * atan2(sqrt($a), sqrt(1 - $a));
    return $earthRadius * $c;
}

/**
 * Interpolates wind data for a grid point using Inverse Distance Weighting.
 * @param float $gridLat Latitude of the grid point
 * @param float $gridLon Longitude of the grid point
 * @param array $cities Array of city weather data
 * @param int $numNearest Number of nearest cities to use
 * @param float $power Power parameter for IDW
 * @return array ['u' => float, 'v' => float]
 */
function interpolatePoint($gridLat, $gridLon, &$cities, $numNearest = 4, $power = 2) {
    // Find nearest cities
    usort($cities, function($a, $b) use ($gridLat, $gridLon) {
        $distA = haversineDistance($gridLat, $gridLon, $a['coord']['Lat'], $a['coord']['Lon']);
        $distB = haversineDistance($gridLat, $gridLon, $b['coord']['Lat'], $b['coord']['Lon']);
        return $distA - $distB;
    });

    $nearestCities = array_slice($cities, 0, $numNearest);

    $totalWeight = 0;
    $weightedU = 0;
    $weightedV = 0;

    foreach ($nearestCities as $city) {
        $dist = haversineDistance($gridLat, $gridLon, $city['coord']['Lat'], $city['coord']['Lon']);
        if ($dist == 0) { // If the grid point is exactly at a city, use its data directly
            $windSpeed = $city['wind']['speed']; // m/s
            $windDeg = $city['wind']['deg'];
            $windRad = deg2rad($windDeg);
            return [
                'u' => -$windSpeed * sin($windRad), 
                'v' => -$windSpeed * cos($windRad)
            ];
        }

        $weight = 1 / pow($dist, $power);
        
        $windSpeed = $city['wind']['speed']; // m/s
        $windDeg = $city['wind']['deg'];
        $windRad = deg2rad($windDeg);

        // Convert to U/V components (meteorological convention)
        $u = -$windSpeed * sin($windRad);
        $v = -$windSpeed * cos($windRad);

        $weightedU += $u * $weight;
        $weightedV += $v * $weight;
        $totalWeight += $weight;
    }

    if ($totalWeight == 0) return ['u' => 0, 'v' => 0];

    return [
        'u' => $weightedU / $totalWeight,
        'v' => $weightedV / $totalWeight
    ];
}


// --- Data Fetching and Processing ---

$bulkFileName = 'weather_14.json.gz';
$bulkUrl = "https://bulk.openweathermap.org/snapshot/{$bulkFileName}?appid=" . OWM_API_KEY;

$gzData = @file_get_contents($bulkUrl);
if ($gzData === false) {
    http_response_code(500);
    echo json_encode(['error' => 'Failed to download bulk weather data. Check API key and URL.']);
    exit;
}

$jsonData = gzdecode($gzData);
if ($jsonData === false) {
    http_response_code(500);
    echo json_encode(['error' => 'Failed to decompress weather data.']);
    exit;
}

// The file contains JSON objects separated by newlines
$lines = explode("\n", trim($jsonData));
$cities = [];
foreach ($lines as $line) {
    if (!empty($line)) {
        $cities[] = json_decode($line, true);
    }
}

if (empty($cities)) {
    http_response_code(500);
    echo json_encode(['error' => 'Failed to parse weather data JSON or file is empty.']);
    exit;
}

// --- Interpolation ---

$nx = 72; // Grid points in longitude (every 5 degrees)
$ny = 37; // Grid points in latitude (every 5 degrees)
$lo1 = -180;
$la1 = 90;
$dx = 5;
$dy = 5;

$uData = [];
$vData = [];

for ($j = 0; $j < $ny; $j++) {
    $lat = $la1 - $j * $dy;
    for ($i = 0; $i < $nx; $i++) {
        $lon = $lo1 + $i * $dx;
        $wind = interpolatePoint($lat, $lon, $cities);
        $uData[] = $wind['u'];
        $vData[] = $wind['v'];
    }
}

// --- Format Data ---

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

$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
    ]
];

// --- Caching and Output ---
$cacheDir = dirname($cacheFile);
if (!is_dir($cacheDir)) {
    mkdir($cacheDir, 0755, true);
}
file_put_contents($cacheFile, json_encode($formattedData));

echo json_encode($formattedData);

?>