<?php
// resolve.php - Multi-Instance Audio Stream Resolver with Fallbacks

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

$artist = $_GET['artist'] ?? '';
$title = $_GET['title'] ?? '';

if (empty($artist) && empty($title)) {
    echo json_encode(['error' => 'Missing artist or title parameters']);
    exit;
}

$query = urlencode(trim("{$artist} - {$title} audio"));

// Primary Invidious Instance Mirrors
$invidiousInstances = [
    "https://inv.privacydev.net",
    "https://yewtu.be",
    "https://invidious.nerdvpn.de",
    "https://invidious.drgns.space"
];

function httpGet(string $url): ?string {
    $ch = curl_init();
    curl_setopt_array($ch, [
        CURLOPT_URL => $url,
        CURLOPT_RETURNTRANSFER => true,
        CURLOPT_FOLLOWLOCATION => true,
        CURLOPT_TIMEOUT => 4,
        CURLOPT_USERAGENT => 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36',
        CURLOPT_SSL_VERIFYPEER => false
    ]);
    $res = curl_exec($ch);
    $code = curl_getinfo($ch, CURLINFO_HTTP_CODE);
    curl_close($ch);
    return ($code === 200 && $res) ? $res : null;
}

// Strategy 1: Loop through Invidious Instances
foreach ($invidiousInstances as $instance) {
    $searchUrl = "{$instance}/api/v1/search?q={$query}&type=video";
    $searchRes = httpGet($searchUrl);
    
    if (!$searchRes) continue;
    
    $searchResults = json_decode($searchRes, true);
    if (empty($searchResults) || !isset($searchResults[0]['videoId'])) continue;

    $videoId = $searchResults[0]['videoId'];
    $videoUrl = "{$instance}/api/v1/videos/{$videoId}";
    $videoRes = httpGet($videoUrl);

    if (!$videoRes) continue;

    $videoDetails = json_decode($videoRes, true);
    $audioStreams = $videoDetails['audioStreams'] ?? [];

    if (!empty($audioStreams)) {
        // Sort streams by bitrate (ascending) for low-memory legacy playback
        usort($audioStreams, function($a, $b) {
            return ($a['bitrate'] ?? 0) <=> ($b['bitrate'] ?? 0);
        });

        echo json_encode([
            'video_id' => $videoId,
            'stream_url' => $audioStreams[0]['url'],
            'engine' => 'invidious',
            'instance' => $instance
        ]);
        exit;
    }
}

// Strategy 2: Fallback to Piped API Mirrors
$pipedInstances = [
    "https://pipedapi.kavin.rocks",
    "https://pipedapi.tokhmi.xyz"
];

foreach ($pipedInstances as $piped) {
    $searchUrl = "{$piped}/search?q={$query}&filter=music_songs";
    $searchRes = httpGet($searchUrl);
    if (!$searchRes) continue;

    $searchResults = json_decode($searchRes, true);
    $items = $searchResults['items'] ?? [];
    if (empty($items)) continue;

    $urlPath = $items[0]['url'] ?? '';
    preg_match('/v=([a-zA-Z0-9_-]+)/', $urlPath, $vMatch);
    $videoId = $vMatch[1] ?? null;

    if (!$videoId) continue;

    $streamUrl = "{$piped}/streams/{$videoId}";
    $streamRes = httpGet($streamUrl);
    if (!$streamRes) continue;

    $streamDetails = json_decode($streamRes, true);
    $audioStreams = $streamDetails['audioStreams'] ?? [];

    if (!empty($audioStreams)) {
        echo json_encode([
            'video_id' => $videoId,
            'stream_url' => $audioStreams[0]['url'],
            'engine' => 'piped',
            'instance' => $piped
        ]);
        exit;
    }
}

echo json_encode(['error' => 'No matching stream found across all backend mirrors']);