// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System.Collections;

namespace System.ComponentModel.Design;

/// <summary>
///  Provides a read-only collection of design surfaces.
/// </summary>
public sealed class DesignSurfaceCollection : ICollection
{
    private readonly DesignerCollection _designers;

    /// <summary>
    ///  Initializes a new instance of the DesignSurfaceCollection class
    /// </summary>
    internal DesignSurfaceCollection(DesignerCollection? designers)
    {
        _designers = designers ?? new DesignerCollection(null);
    }

    /// <summary>
    ///  Gets number of design surfaces in the collection.
    /// </summary>
    public int Count => _designers.Count;

    /// <summary>
    ///  Gets or sets the document at the specified index.
    /// </summary>
    public DesignSurface this[int index]
    {
        get
        {
            IDesignerHost host = _designers[index]!;
            if (host.GetService(typeof(DesignSurface)) is DesignSurface surface)
            {
                return surface;
            }

            throw new NotSupportedException();
        }
    }

    /// <summary>
    ///  Creates and retrieves a new enumerator for this collection.
    /// </summary>
    public IEnumerator GetEnumerator() => new DesignSurfaceEnumerator(_designers.GetEnumerator());

    int ICollection.Count => Count;

    bool ICollection.IsSynchronized => false;

    object ICollection.SyncRoot => null!;

    void ICollection.CopyTo(Array array, int index)
    {
        foreach (DesignSurface surface in this)
        {
            array.SetValue(surface, index++);
        }
    }

    public void CopyTo(DesignSurface[] array, int index) => ((ICollection)this).CopyTo(array, index);

    IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();

    /// <summary>
    ///  Enumerator that performs the conversion from designer host
    ///  to design surface.
    /// </summary>
    private class DesignSurfaceEnumerator : IEnumerator
    {
        private readonly IEnumerator _designerEnumerator;

        internal DesignSurfaceEnumerator(IEnumerator designerEnumerator)
        {
            _designerEnumerator = designerEnumerator;
        }

        public object Current
        {
            get
            {
                IDesignerHost host = (IDesignerHost)_designerEnumerator.Current!;
                if (host.GetService(typeof(DesignSurface)) is DesignSurface surface)
                {
                    return surface;
                }

                throw new NotSupportedException();
            }
        }

        public bool MoveNext() => _designerEnumerator.MoveNext();

        public void Reset() => _designerEnumerator.Reset();
    }
}
