<?php
ini_set('display_errors', 1);
ini_set('display_startup_errors', 1);
error_reporting(E_ALL);

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

// --- Configuration ---
$gfs_url = 'https://nomads.ncep.noaa.gov/pub/data/nccf/com/gfs/prod/gfs.20251013/00/atmos/gfs.t00z.pgrb2.0p25.f000';
$tmp_dir = '/tmp';
$grib_file = $tmp_dir . '/' . basename($gfs_url);
$xyz_file = $tmp_dir . '/gfs.xyz';

// --- Download the GFS file ---
if (!file_exists($grib_file)) {
    $fp = fopen($grib_file, 'w');
    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL, $gfs_url);
    curl_setopt($ch, CURLOPT_FILE, $fp);
    curl_setopt($ch, CURLOPT_FOLLOWLOCATION, 1);
    curl_exec($ch);
    $http_code = curl_getinfo($ch, CURLINFO_HTTP_CODE);
    curl_close($ch);
    fclose($fp);

    if ($http_code !== 200) {
        unlink($grib_file); // Clean up failed download
        echo json_encode(['error' => 'Failed to download GFS file', 'http_code' => $http_code]);
        exit;
    }
}

// --- Convert GRIB to XYZ using gdal_translate ---
// We'll use band 1 for this example. You can use gdalinfo to see available bands.
$gdal_command = 'gdal_translate -b 1 -of XYZ ' . escapeshellarg($grib_file) . ' ' . escapeshellarg($xyz_file);
$gdal_output = shell_exec($gdal_command);

if (!file_exists($xyz_file)) {
    echo json_encode(['error' => 'Failed to convert GRIB to XYZ', 'gdal_output' => $gdal_output]);
    unlink($grib_file);
    exit;
}

// --- Read the XYZ file and create GeoJSON features ---
$features = [];
$handle = fopen($xyz_file, 'r');
$line_count = 0;
$sample_rate = 100; // Process 1 in every 100 lines

if ($handle) {
    while (($line = fgets($handle)) !== false) {
        $line_count++;
        if ($line_count % $sample_rate !== 0) {
            continue;
        }

        $parts = preg_split('/\s+/', trim($line));
        if (count($parts) === 3) {
            $lon = floatval($parts[0]);
            $lat = floatval($parts[1]);
            $value = floatval($parts[2]);

            // Skip points that are exactly zero, often represent no data
            if ($value === 0.0) {
                continue;
            }

            $features[] = [
                'type' => 'Feature',
                'properties' => ['value' => $value],
                'geometry' => [
                    'type' => 'Point',
                    'coordinates' => [$lon, $lat]
                ]
            ];
        }
    }
    fclose($handle);
}

// --- Clean up temporary files ---
unlink($grib_file);
unlink($xyz_file);

// --- Output the GeoJSON ---
echo json_encode([
    'type' => 'FeatureCollection',
    'features' => $features
]);

?>