namespace Vanara.InteropServices;

/// <summary>Factory for creating <see cref="ComReleaser{T}"/> objects.</summary>
public static class ComReleaserFactory
{
	/// <summary>Factory method to create a <see cref="ComReleaser{TObj}"/> using type inference.</summary>
	/// <typeparam name="TObj">The type of the object.</typeparam>
	/// <param name="obj">The object.</param>
	/// <returns>A <see cref="ComReleaser{TObj}"/> instance.</returns>
	public static ComReleaser<TObj> Create<TObj>(TObj obj) where TObj : class => new(obj);
}

/// <summary>A safe variable to hold an instance of a COM class that automatically releases the instance on disposal.</summary>
/// <typeparam name="T">The type of the COM object.</typeparam>
/// <seealso cref="IDisposable"/>
public class ComReleaser<T> : IDisposable where T : class
{
	private T? item;

	/// <summary>Initializes a new instance of the <see cref="ComReleaser{T}"/> class.</summary>
	/// <param name="obj">The COM object instance.</param>
	/// <exception cref="ArgumentNullException">obj</exception>
	/// <exception cref="ArgumentException">Argument value must be a COM object. - obj</exception>
	public ComReleaser(T obj)
	{
		if (obj == null) throw new ArgumentNullException(nameof(obj));
		if (!obj.GetType().IsCOMObject) throw new ArgumentException("Argument value must be a COM object.", nameof(obj));
		item = obj;
	}

	/// <summary>Initializes a new instance of the <see cref="ComReleaser{T}"/> class.</summary>
	/// <param name="obj">The COM object instance.</param>
	/// <exception cref="ArgumentNullException">obj</exception>
	/// <exception cref="ArgumentException">Argument value must be a COM object and expose <typeparamref name="T"/>.</exception>
	public ComReleaser(object obj)
	{
		if (!obj.GetType().IsCOMObject) throw new ArgumentException("Argument value must be a COM object.", nameof(obj));
		item = obj is T t ? t : throw new ArgumentException($"Object must expose the {typeof(T).Name} interface.");
	}

	/// <summary>Gets the COM object.</summary>
	/// <value>The COM object.</value>
	public T Item => item ?? throw new ObjectDisposedException(nameof(ComReleaser<T>));

	/// <summary>Performs an implicit conversion from <typeparamref name="T"/> to <see cref="ComReleaser{T}"/>.</summary>
	/// <param name="obj">The COM object.</param>
	/// <returns>The result of the conversion.</returns>
	public static explicit operator ComReleaser<T>(T obj) => new(obj);

	/// <summary>Performs an implicit conversion from <see cref="ComReleaser{T}"/> to <typeparamref name="T"/>.</summary>
	/// <param name="co">The <see cref="ComReleaser{T}"/> instance.</param>
	/// <returns>The result of the conversion.</returns>
	public static explicit operator T(ComReleaser<T> co) => co.Item;

	/// <summary>Performs application-defined tasks associated with freeing, releasing, or resetting unmanaged resources.</summary>
	public void Dispose() => item = null;
}