Error+SyncRetry.swift

extension Error {
    var code: Int { return (self as NSError).code }
    var domain: String { return (self as NSError).domain }
    var userInfo: [String:Any] { return (self as NSError).userInfo }

    func timeAfterWhichToRetry(retryCount: Int) -> TimeInterval? {
        // CloudKit suggests us retry too often, so slow us down as we retry a lot, up to 5 minutes
        if let suggestedTimeout = suggestedTimeAfterWhichToRetry {
            if suggestedTimeAfterWhichToRetry == 0 {
                return 0
            }
            else {
                return max(min(5.0 * 60.0, TimeInterval(retryCount) * 10.0), suggestedTimeout)
            }
        }
        else {
            return nil
        }
    }
    
    private var suggestedTimeAfterWhichToRetry: TimeInterval? {
        if domain == CKErrorDomain && code == CKError.quotaExceeded.rawValue {
            return nil
        }
        
        // If we are rate limited because we previously failed because the user ran out of iCloud space, we want to immediately stop and show them that error
        if domain == CKErrorDomain, code == CKError.requestRateLimited.rawValue, let errorDescription = userInfo["CKErrorDescription"] as? String, errorDescription.contains("Quota exceeded") {
            return nil
        }
        
        if let retryAfter = userInfo[CKErrorRetryAfterKey] as? TimeInterval {
            return retryAfter
        }
        
        if domain == CKErrorDomain && code == CKError.partialFailure.rawValue,
           let ckError = self as? CKError, let suberrors = ckError.partialErrorsByItemID?.values,
           let timeout = suberrors.compactMap({ $0.suggestedTimeAfterWhichToRetry }).first {
               return timeout
       }
        
        switch self {
        case URLError.timedOut, URLError.notConnectedToInternet, URLError.secureConnectionFailed: // Transient network issues that seems like they might resolve quickly
            return 10
        case CKError.zoneBusy, CKError.requestRateLimited: // Expect this to have a retryAfter, but sometimes it doesn't
            return 30
        default:
            return nil
        }
    }
}