using System;
using System.Collections.Generic;

namespace Python.Runtime.Codecs
{
 public class SequenceDecoder : IPyObjectDecoder
 {
 internal static bool IsSequence(Type targetType)
 {
 if (!targetType.IsGenericType)
 return false;

 return targetType.GetGenericTypeDefinition() == typeof(ICollection<>);
 }

 internal static bool IsSequence(PyType objectType)
 {
 //must implement iterable protocol to fully implement sequence protocol
 if (!IterableDecoder.IsIterable(objectType)) return false;

 //returns wheter it implements the sequence protocol
 //according to python doc this needs to exclude dict subclasses
 //but I don't know how to look for that given the objectType
 //rather than the instance.
 return objectType.HasAttr("__getitem__");
 }

 public bool CanDecode(PyType objectType, Type targetType)
 {
 return IsSequence(objectType) && IsSequence(targetType);
 }

 public bool TryDecode<T>(PyObject pyObj, out T value)
 {
 if (pyObj == null) throw new ArgumentNullException(nameof(pyObj));

 var elementType = typeof(T).GetGenericArguments()[0];
 Type collectionType = typeof(CollectionWrappers.SequenceWrapper<>).MakeGenericType(elementType);

 var instance = Activator.CreateInstance(collectionType, new[] { pyObj });
 value = (T)instance;
 return true;
 }

 public static SequenceDecoder Instance { get; } = new SequenceDecoder();

 public static void Register()
 {
 PyObjectConversions.RegisterDecoder(Instance);
 }
 }
}