namespace Python.Runtime.Codecs
{
 using System;
 using System.Collections;
 using System.Collections.Generic;
 using System.Linq;

 /// <summary>
 /// Represents a group of <see cref="IPyObjectDecoder"/>s. Useful to group them by priority.
 /// </summary>
 public sealed class DecoderGroup: IPyObjectDecoder, IEnumerable<IPyObjectDecoder>, IDisposable
 {
 readonly List<IPyObjectDecoder> decoders = new();

 /// <summary>
 /// Add specified decoder to the group
 /// </summary>
 public void Add(IPyObjectDecoder item)
 {
 if (item is null) throw new ArgumentNullException(nameof(item));

 this.decoders.Add(item);
 }
 /// <summary>
 /// Remove all decoders from the group
 /// </summary>
 public void Clear() => this.decoders.Clear();

 /// <inheritdoc />
 public bool CanDecode(PyType objectType, Type targetType)
 => this.decoders.Any(decoder => decoder.CanDecode(objectType, targetType));
 /// <inheritdoc />
 public bool TryDecode<T>(PyObject pyObj, out T? value)
 {
 if (pyObj is null) throw new ArgumentNullException(nameof(pyObj));

 var decoder = this.GetDecoder(pyObj.GetPythonType(), typeof(T));
 if (decoder is null)
 {
 value = default;
 return false;
 }
 return decoder.TryDecode(pyObj, out value);
 }

 /// <inheritdoc />
 public IEnumerator<IPyObjectDecoder> GetEnumerator() => this.decoders.GetEnumerator();
 IEnumerator IEnumerable.GetEnumerator() => this.decoders.GetEnumerator();

 public void Dispose()
 {
 foreach (var decoder in this.decoders.OfType<IDisposable>())
 {
 decoder.Dispose();
 }
 this.decoders.Clear();
 }
 }

 public static class DecoderGroupExtensions
 {
 /// <summary>
 /// Gets a concrete instance of <see cref="IPyObjectDecoder"/>
 /// (potentially selecting one from a collection),
 /// that can decode from <paramref name="objectType"/> to <paramref name="targetType"/>,
 /// or <c>null</c> if a matching decoder can not be found.
 /// </summary>
 public static IPyObjectDecoder? GetDecoder(
 this IPyObjectDecoder decoder,
 PyType objectType, Type targetType)
 {
 if (decoder is null) throw new ArgumentNullException(nameof(decoder));

 if (decoder is IEnumerable<IPyObjectDecoder> composite)
 {
 return composite
 .Select(nestedDecoder => nestedDecoder.GetDecoder(objectType, targetType))
 .FirstOrDefault(d => d != null);
 }

 return decoder.CanDecode(objectType, targetType) ? decoder : null;
 }
 }
}