import SwiftUI
import Firebase
import FirebaseFirestore
import Combine

protocol BaseModel: Identifiable, Codable {
    var id: String? { get set }
    var collection: String { get }
    init()
}

class BaseViewModel<T: BaseModel>: ObservableObject, Identifiable, Equatable {

    @Published var model: T
    var id: String {
        didSet {
            self.model.id = id
        }
    }
    
    var cancellables = [AnyCancellable]()
    private var db = Firestore.firestore()
    
    required init(){
        let model = T.init()
        self.model = model
        self.id = model.id ?? UUID().uuidString
    }
    
    required init(id: String) {
        var model = T.init()
        model.id = id
        self.model = model
        self.id = id
    }
    
    init(model: T) {
        self.model = model
        self.id = model.id ?? UUID().uuidString
    }

    static func ==(lhs: BaseViewModel<T>, rhs: BaseViewModel<T>) -> Bool {
        lhs.model.id == rhs.model.id
    }
    
    func load(completion: @escaping (Bool) -> Void = {finished in}){
        if let id = model.id {
            self.id = id
            db.collection(model.collection).document(id).getDocument { docSnapshot, error in
                guard let doc = docSnapshot else {
                    print("Error fetching document: \(error!)")
                    return
                }
                
                do {
                    guard let data = try doc.data(as: T.self) else {
                        print("Document empty \(type(of: self.model)) with id \(id)")
                        return
                    }
                    self.model = data
                    self.loadSubData {finished in
                        if finished{
                            completion(true)
                        }
                    }
                } catch {
                    print(error.localizedDescription)
                }
            }
        }
    }
    
    func loadSubData(completion: @escaping(Bool) -> Void = {finished in}) {
        fatalError("Must be overridden!")
    }
    
    func loadDataByIDs<T, S>(from list: [String], appender: @escaping (T) -> Void) where T: BaseViewModel<S>, S: BaseModel {
        for id in list {
            let viewModel = T.init(id: id)
            viewModel.load{finished in
                if finished {
                    appender(viewModel)
                }
            }
        }
    }
    
    func save(){
        do {
            let _ = try db.collection(model.collection).addDocument(from: model)
        } catch {
            print(error)
        }
    }
    
    func update(){
        if let id = model.id {
            do {
                try db.collection(model.collection).document(id).setData(from: model)
            } catch {
                print(error.localizedDescription)
            }
        }
    }
    
    func delete(){
        if let id = model.id {
            db.collection(model.collection).document(id).delete() { error in
                if let error = error {
                    print(error.localizedDescription)
                }
            }
        }
    }
    
}