using System.Collections.Generic;
using StardewModdingAPI.Framework.StateTracking;

namespace StardewModdingAPI.Framework
{
    /// <summary>A snapshot of a tracked list.</summary>
    /// <typeparam name="T">The tracked list value type.</typeparam>
    internal class SnapshotListDiff<T>
    {
        /*********
        ** Fields
        *********/
        /// <summary>The removed values.</summary>
        private readonly List<T> RemovedImpl = new();

        /// <summary>The added values.</summary>
        private readonly List<T> AddedImpl = new();


        /*********
        ** Accessors
        *********/
        /// <summary>Whether the value changed since the last update.</summary>
        public bool IsChanged { get; private set; }

        /// <summary>The removed values.</summary>
        public IEnumerable<T> Removed => this.RemovedImpl;

        /// <summary>The added values.</summary>
        public IEnumerable<T> Added => this.AddedImpl;


        /*********
        ** Public methods
        *********/
        /// <summary>Update the snapshot.</summary>
        /// <param name="isChanged">Whether the value changed since the last update.</param>
        /// <param name="removed">The removed values.</param>
        /// <param name="added">The added values.</param>
        public void Update(bool isChanged, IEnumerable<T>? removed, IEnumerable<T>? added)
        {
            this.IsChanged = isChanged;

            this.RemovedImpl.Clear();
            if (removed != null)
                this.RemovedImpl.AddRange(removed);

            this.AddedImpl.Clear();
            if (added != null)
                this.AddedImpl.AddRange(added);
        }

        /// <summary>Update the snapshot.</summary>
        /// <param name="watcher">The value watcher to snapshot.</param>
        public void Update(ICollectionWatcher<T> watcher)
        {
            this.Update(watcher.IsChanged, watcher.Removed, watcher.Added);
        }
    }
}