using System;
using System.Collections.ObjectModel;
using Firebase.Database.Streaming;

namespace Firebase.Database {
    /// <summary>
    ///     Extensions for <see cref="IObservable{T}" />.
    /// </summary>
    public static class ObservableExtensions {
        /// <summary>
        ///     Starts observing on given firebase observable and propagates event into an <see cref="ObservableCollection{T}" />.
        /// </summary>
        /// <param name="observable"> The observable. </param>
        /// <typeparam name="T"> Type of entity. </typeparam>
        /// <returns> The <see cref="ObservableCollection{T}" />. </returns>
        public static ObservableCollection<T> AsObservableCollection<T>(this IObservable<FirebaseEvent<T>> observable) {
            var collection = new ObservableCollection<T>();

            observable.Subscribe(f => {
                if (f.EventType == FirebaseEventType.InsertOrUpdate) {
                    var i = collection.IndexOf(f.Object);
                    if (i >= 0) collection.RemoveAt(i);

                    collection.Add(f.Object);
                }
                else {
                    collection.Remove(f.Object);
                }
            });

            return collection;
        }
    }
}