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#nullable disable
using System.Collections.Generic;
using System.Linq;
namespace StardewModdingAPI.Framework.StateTracking.FieldWatchers
{
/// <summary>A watcher which detects changes to a collection of values using a specified <see cref="IEqualityComparer{T}"/> instance.</summary>
/// <typeparam name="TValue">The value type within the collection.</typeparam>
internal class ComparableListWatcher<TValue> : BaseDisposableWatcher, ICollectionWatcher<TValue>
{
/*********
** Fields
*********/
/// <summary>The collection to watch.</summary>
private readonly ICollection<TValue> CurrentValues;
/// <summary>The values during the previous update.</summary>
private HashSet<TValue> LastValues;
/// <summary>The pairs added since the last reset.</summary>
private readonly List<TValue> AddedImpl = new();
/// <summary>The pairs removed since the last reset.</summary>
private readonly List<TValue> RemovedImpl = new();
/*********
** Accessors
*********/
/// <summary>Whether the value changed since the last reset.</summary>
public bool IsChanged => this.AddedImpl.Count > 0 || this.RemovedImpl.Count > 0;
/// <summary>The values added since the last reset.</summary>
public IEnumerable<TValue> Added => this.AddedImpl;
/// <summary>The values removed since the last reset.</summary>
public IEnumerable<TValue> Removed => this.RemovedImpl;
/*********
** Public methods
*********/
/// <summary>Construct an instance.</summary>
/// <param name="values">The collection to watch.</param>
/// <param name="comparer">The equality comparer which indicates whether two values are the same.</param>
public ComparableListWatcher(ICollection<TValue> values, IEqualityComparer<TValue> comparer)
{
this.CurrentValues = values;
this.LastValues = new HashSet<TValue>(comparer);
}
/// <summary>Update the current value if needed.</summary>
public void Update()
{
this.AssertNotDisposed();
// optimize for zero items
if (this.CurrentValues.Count == 0)
{
if (this.LastValues.Count > 0)
{
this.AddedImpl.AddRange(this.LastValues);
this.LastValues.Clear();
}
return;
}
// detect changes
HashSet<TValue> curValues = new HashSet<TValue>(this.CurrentValues, this.LastValues.Comparer);
this.RemovedImpl.AddRange(from value in this.LastValues where !curValues.Contains(value) select value);
this.AddedImpl.AddRange(from value in curValues where !this.LastValues.Contains(value) select value);
this.LastValues = curValues;
}
/// <summary>Set the current value as the baseline.</summary>
public void Reset()
{
this.AssertNotDisposed();
this.AddedImpl.Clear();
this.RemovedImpl.Clear();
}
}
}
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