ObjectMapper date transform (formatter) for FIRServerValue.timestamp(). Firebase's timestamp.

FirebaseDateTransform

import Foundation
import ObjectMapper

open class FirebaseDateTransform: TransformType {
    public typealias Object = Date
    public typealias JSON = Double
    
    public init() {}
    
    open func transformFromJSON(_ value: Any?) -> Date? {
        if let t = value as? TimeInterval {
            return Date(timeIntervalSince1970: t/1000)
        }
        return nil
    }
    
    open func transformToJSON(_ value: Date?) -> Double? {
        if let date = value {
            return Double(date.timeIntervalSince1970)
        }
        return nil
    }
}

There is an error in the transformToJSON. Should be multiplied by 1000.