using System.Collections.ObjectModel;
using System.Collections.Specialized;
using Xunit;

namespace ZymonicServices.Performance.Tests;

public class CollectionProjectionTests
{
    [Fact]
    public void UnchangedProjectionDoesNotNotify()
    {
        var item = new object();
        var target = new ObservableCollection<object> { item };
        target.CollectionChanged += (_, _) => Assert.Fail("Unchanged projection notified the UI.");
        ZymonicCollectionProjection.Apply(target, new[] { item });
    }

    [Fact]
    public void ReordersAddsAndRemovesWithoutResettingRetainedItems()
    {
        var a = new object(); var b = new object(); var c = new object(); var d = new object();
        var target = new ObservableCollection<object> { a, b, c };
        var actions = new List<NotifyCollectionChangedAction>();
        target.CollectionChanged += (_, e) => actions.Add(e.Action);
        ZymonicCollectionProjection.Apply(target, new[] { c, d, a });
        Assert.Equal(new[] { c, d, a }, target);
        Assert.DoesNotContain(NotifyCollectionChangedAction.Reset, actions);
        Assert.Contains(NotifyCollectionChangedAction.Move, actions);
        ZymonicCollectionProjection.Apply(target, Array.Empty<object>());
        Assert.Empty(target);
        Assert.DoesNotContain(NotifyCollectionChangedAction.Reset, actions);
    }

    private sealed record Value(int Id);

    [Fact]
    public void EqualValuesStillReplaceOldInstance()
    {
        var old = new Value(1); var replacement = new Value(1);
        var target = new ObservableCollection<Value> { old };
        ZymonicCollectionProjection.Apply(target, new[] { replacement });
        Assert.Same(replacement, Assert.Single(target));
    }

    [Fact]
    public void DuplicateDesiredInstanceIsRejectedBeforeMutation()
    {
        var item = new object();
        var target = new ObservableCollection<object> { item };
        Assert.Throws<ArgumentException>(() => ZymonicCollectionProjection.Apply(target, new[] { item, item }));
        Assert.Same(item, Assert.Single(target));
    }
}