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

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

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

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

        /// 
        public bool CanDecode(PyObject objectType, Type targetType)
            => this.decoders.Any(decoder => decoder.CanDecode(objectType, targetType));
        /// 
        public bool TryDecode(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);
        }

        /// 
        public IEnumerator GetEnumerator() => this.decoders.GetEnumerator();
        IEnumerator IEnumerable.GetEnumerator() => this.decoders.GetEnumerator();
    }

    public static class DecoderGroupExtensions
    {
        /// 
        /// Gets a concrete instance of 
        /// (potentially selecting one from a collection),
        /// that can decode from  to ,
        /// or null if a matching decoder can not be found.
        /// 
        public static IPyObjectDecoder GetDecoder(
            this IPyObjectDecoder decoder,
            PyObject objectType, Type targetType)
        {
            if (decoder is null) throw new ArgumentNullException(nameof(decoder));

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

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