//
//  TrainDetailViewModel.swift
//  LunchTrain
//
//

import Foundation
import FirebaseFirestore

class TrainDetailViewModel {
    var didChangeData: ((TrainDetailViewData) -> Void)?
    var trainReference: DocumentReference?
    var localCollection: LocalCollection<User>!

    fileprivate var query: Query? {
        didSet {
            if let listener = listener {
                listener.remove()
                observeQuery()
            }
        }
    }

    private var listener: ListenerRegistration?
    var documents: [DocumentSnapshot] = []

    var viewData: TrainDetailViewData {
        didSet {
            didChangeData?(viewData)
        }
    }

    init(viewData: TrainDetailViewData) {
        self.viewData = viewData
        query = baseQuery()
    }

    func observeQuery() {
        guard let query = query else { return }
        stopObserving()

        listener = query.addSnapshotListener { [unowned self] (snapshot, error) in
            guard let snapshot = snapshot else {
                print("Error fetching snapshot results: \(error!)")
                return
            }

            let models = snapshot.documents.compactMap { (document) -> User? in
                if let model = User(dictionary: document.data()) {
                    return model
                } else {
                    print("error parsing document: \(document.data())")
                    return nil
                }
            }

            self.viewData.passengers = models
            self.documents = snapshot.documents
        }
    }

    func stopObserving() {
        listener?.remove()
    }

    fileprivate func baseQuery() -> Query? {
        return trainReference?.collection("passengers")
    }
}