CREATE TABLE api_keys (
 id INTEGER PRIMARY KEY AUTOINCREMENT,
 key_val TEXT NOT NULL UNIQUE,
 provider TEXT NOT NULL DEFAULT 'youtube',
 quota_used INTEGER NOT NULL DEFAULT 0,
 quota_limit INTEGER NOT NULL DEFAULT 10000,
 quota_reset TEXT, -- ISO 8601 UTC timestamp of next reset
 is_active INTEGER NOT NULL DEFAULT 1,
 error_count INTEGER NOT NULL DEFAULT 0,
 last_error TEXT,
 created_at TEXT DEFAULT (datetime('now'))
);

CREATE INDEX idx_api_keys_active ON api_keys(provider, is_active, quota_used);

<?php

class QuotaManager
{
 private PDO $db;
 private ?array $activeKey = null;

 public function __construct(PDO $db)
 {
 $this->db = $db;
 }

 /**
 * Get the key with most remaining quota.
 * Returns null if all keys are exhausted.
 */
 public function getActiveKey(): ?array
 {
 if ($this->activeKey !== null) {
 return $this->activeKey;
 }

 $stmt = $this->db->prepare(<<<SQL
 SELECT *
 FROM api_keys
 WHERE provider = 'youtube'
 AND is_active = 1
 AND (quota_used < quota_limit)
 AND (
 quota_reset IS NULL
 OR quota_reset < datetime('now')
 OR quota_used < quota_limit
 )
 ORDER BY (quota_limit - quota_used) DESC
 LIMIT 1
 SQL);
 $stmt->execute();

 $this->activeKey = $stmt->fetch(PDO::FETCH_ASSOC) ?: null;
 return $this->activeKey;
 }

 public function consume(string $keyVal, int $units): void
 {
 $this->db->prepare(<<<SQL
 UPDATE api_keys
 SET quota_used = quota_used + ?,
 quota_reset = COALESCE(
 quota_reset,
 datetime('now', '+1 day', 'start of day')
 )
 WHERE key_val = ?
 SQL)->execute([$units, $keyVal]);

 // Bust the in-memory cache so next call re-fetches
 $this->activeKey = null;
 }

 public function markError(string $keyVal, string $error): void
 {
 $this->db->prepare(<<<SQL
 UPDATE api_keys
 SET error_count = error_count + 1,
 last_error = ?,
 is_active = CASE WHEN error_count >= 5 THEN 0 ELSE is_active END
 WHERE key_val = ?
 SQL)->execute([$error, $keyVal]);

 $this->activeKey = null;
 }

 public function canFetch(int $unitsNeeded = 1): bool
 {
 $key = $this->getActiveKey();
 if ($key === null) {
 return false;
 }
 return ($key['quota_limit'] - $key['quota_used']) >= $unitsNeeded;
 }

 public function resetDailyQuotas(): void
 {
 // Called at midnight UTC by cron
 $this->db->exec(<<<SQL
 UPDATE api_keys
 SET quota_used = 0,
 error_count = 0,
 is_active = 1,
 quota_reset = NULL
 WHERE quota_reset < datetime('now')
 SQL);
 }
}

<?php

class YouTubeApi
{
 private QuotaManager $quota;
 private int $retryDelay = 2; // seconds

 public function __construct(QuotaManager $quota)
 {
 $this->quota = $quota;
 }

 public function fetchTrending(string $region, int $maxResults = 50): array
 {
 $key = $this->quota->getActiveKey();
 if ($key === null) {
 throw new QuotaExhaustedException("All API keys exhausted for region {$region}");
 }

 $url = 'https://www.googleapis.com/youtube/v3/videos?' . http_build_query([
 'part' => 'snippet,statistics,contentDetails',
 'chart' => 'mostPopular',
 'regionCode' => $region,
 'maxResults' => $maxResults,
 'videoCategoryId' => '',
 'key' => $key['key_val'],
 ]);

 $response = $this->get($url);

 if ($response['http_code'] === 403) {
 // Quota exceeded — disable this key, try next
 $this->quota->markError($key['key_val'], 'quota_exceeded');
 $this->quota->consume($key['key_val'], $key['quota_limit']); // Force exhaustion
 return $this->fetchTrending($region, $maxResults); // Recurse with next key
 }

 if ($response['http_code'] !== 200) {
 $this->quota->markError($key['key_val'], "HTTP {$response['http_code']}");
 throw new ApiException("YouTube API error: {$response['http_code']}");
 }

 // Charge the quota: 1 unit for videos.list
 $this->quota->consume($key['key_val'], 1);

 $body = json_decode($response['body'], true);
 return $body['items'] ?? [];
 }

 private function get(string $url): array
 {
 $ch = curl_init($url);
 curl_setopt_array($ch, [
 CURLOPT_RETURNTRANSFER => true,
 CURLOPT_TIMEOUT => 20,
 CURLOPT_FOLLOWLOCATION => true,
 CURLOPT_HTTPHEADER => ['Accept: application/json'],
 ]);
 $body = curl_exec($ch);
 $httpCode = curl_getinfo($ch, CURLINFO_HTTP_CODE);
 $error = curl_error($ch);
 curl_close($ch);

 if ($error) {
 throw new NetworkException("cURL error: {$error}");
 }

 return ['http_code' => $httpCode, 'body' => $body];
 }
}

<?php

class RegionBudget
{
 // Units per day per region for search
 private const BUDGETS = [
 'JP' => 2000, // High-traffic
 'KR' => 2000,
 'US' => 1500,
 'GB' => 1000,
 'TW' => 800,
 'SG' => 600,
 'HK' => 600,
 'VN' => 400,
 'TH' => 400,
 ];

 public function canSearch(string $region): bool
 {
 $used = $this->getUsedToday($region);
 $budget = self::BUDGETS[$region] ?? 200;
 return $used + 100 <= $budget;
 }

 private function getUsedToday(string $region): int
 {
 // Read from SQLite daily_budget table
 $stmt = $this->db->prepare(<<<SQL
 SELECT COALESCE(SUM(units_used), 0)
 FROM quota_log
 WHERE region = ? AND DATE(used_at) = DATE('now')
 SQL);
 $stmt->execute([$region]);
 return (int) $stmt->fetchColumn();
 }
}

<?php

class CircuitBreaker
{
 private const THRESHOLD = 5; // failures before opening
 private const TIMEOUT = 300; // seconds before half-open

 public function isOpen(string $service): bool
 {
 $state = $this->getState($service);
 if ($state['status'] === 'open') {
 if (time() - $state['opened_at'] > self::TIMEOUT) {
 $this->halfOpen($service);
 return false; // Allow one test request
 }
 return true; // Still open
 }
 return false;
 }

 public function recordSuccess(string $service): void
 {
 $this->setState($service, ['status' => 'closed', 'failures' => 0]);
 }

 public function recordFailure(string $service): void
 {
 $state = $this->getState($service);
 $failures = ($state['failures'] ?? 0) + 1;

 if ($failures >= self::THRESHOLD) {
 $this->setState($service, [
 'status' => 'open',
 'failures' => $failures,
 'opened_at' => time(),
 ]);
 error_log("Circuit breaker OPEN for {$service}");
 } else {
 $this->setState($service, ['status' => 'closed', 'failures' => $failures]);
 }
 }
}

<?php

// api_keys.conf (deployed alongside the app)
// youtube_key=AIzaSyABC123...
// youtube_key=AIzaSyDEF456...
// youtube_key=AIzaSyGHI789...

public function autoImportApiKeys(): void
{
 $conf = parse_ini_file(__DIR__ . '/../api_keys.conf', false, INI_SCANNER_RAW);
 $keys = (array)($conf['youtube_key'] ?? []);

 $stmt = $this->pdo->prepare(<<<SQL
 INSERT OR IGNORE INTO api_keys (key_val, provider)
 VALUES (?, 'youtube')
 SQL);

 foreach ($keys as $key) {
 $stmt->execute([trim($key)]);
 }
}