<?php
if ($argc < 3 || $argc > 4) {
    fwrite(STDERR, "Usage: php download-file.php <url> <destination> [expected-bytes]\n");
    exit(64);
}

$url = $argv[1];
$destination = $argv[2];
$expectedBytes = null;

if (isset($argv[3])) {
    if (!ctype_digit($argv[3])) {
        fwrite(STDERR, "Expected bytes must be a whole number.\n");
        exit(64);
    }
    $expectedBytes = (int) $argv[3];
}

$scheme = strtolower((string) parse_url($url, PHP_URL_SCHEME));
if (!in_array($scheme, ['http', 'https'], true)) {
    fwrite(STDERR, "URL must use http or https.\n");
    exit(64);
}

$directory = dirname($destination);
if (!is_dir($directory) && !mkdir($directory, 0700, true)) {
    fwrite(STDERR, "Could not create destination directory: {$directory}\n");
    exit(1);
}

$temporary = $destination . '.part';
$file = fopen($temporary, 'wb');
if ($file === false) {
    fwrite(STDERR, "Could not open temporary file: {$temporary}\n");
    exit(1);
}

$curl = curl_init($url);
if ($curl === false) {
    fclose($file);
    @unlink($temporary);
    fwrite(STDERR, "Could not initialize cURL.\n");
    exit(1);
}

curl_setopt_array($curl, [
    CURLOPT_FILE => $file,
    CURLOPT_FOLLOWLOCATION => true,
    CURLOPT_MAXREDIRS => 5,
    CURLOPT_CONNECTTIMEOUT => 10,
    CURLOPT_TIMEOUT => 60,
    CURLOPT_USERAGENT => 'ExampleDownloader/1.0',
]);

$success = curl_exec($curl);
$status = curl_getinfo($curl, CURLINFO_HTTP_CODE);
$error = curl_error($curl);
curl_close($curl);
fclose($file);

if ($success === false) {
    @unlink($temporary);
    fwrite(STDERR, "cURL error: {$error}\n");
    exit(1);
}

if ($status < 200 || $status >= 300) {
    @unlink($temporary);
    fwrite(STDERR, "HTTP status: {$status}\n");
    fwrite(STDERR, "Download failed; temporary file removed.\n");
    exit(1);
}

$bytes = filesize($temporary);
if ($bytes === false) {
    @unlink($temporary);
    fwrite(STDERR, "Could not read downloaded file size.\n");
    exit(1);
}

if ($expectedBytes !== null && $bytes !== $expectedBytes) {
    @unlink($temporary);
    fwrite(STDERR, "Size mismatch: expected {$expectedBytes} bytes, got {$bytes} bytes.\n");
    exit(1);
}

if (!rename($temporary, $destination)) {
    @unlink($temporary);
    fwrite(STDERR, "Could not move temporary file into place.\n");
    exit(1);
}

echo "HTTP status: {$status}\n";
echo "Saved: {$destination}\n";
echo "Bytes: {$bytes}\n";