// Copyright (c) The Geekeey Authors
// SPDX-License-Identifier: EUPL-1.2

using System.Collections;
using System.Collections.Concurrent;

using Microsoft.Extensions.DependencyInjection;

namespace Geekeey.Request.Validation;

internal sealed class ValidationOptions
{
	private readonly List<Type> _search = [];
	private readonly Lazy<TypeIndex> _validatorsTypeIndex;

	public ValidationOptions()
	{
		_validatorsTypeIndex = new Lazy<TypeIndex>(() => new ValidatorTypeIndex(_search.Distinct()));
	}

	public void Inspect(IEnumerable<Type> assembly)
	{
		if (_validatorsTypeIndex.IsValueCreated)
		{
			throw new InvalidOperationException("The type index has already been created. Cannot inspect new assemblies.");
		}

		_search.AddRange(assembly);
	}

	public IEnumerable<IValidator<T>> GetValidators<T>(IServiceProvider services)
	{
		return _validatorsTypeIndex.Value.Resolve<IValidator<T>>(services);
	}

	private abstract class TypeIndex
	{
		private readonly ConcurrentDictionary<Type, Func<IServiceProvider, IEnumerable>> _cache = new();

		protected readonly Dictionary<Type, List<Type>> _closedTypeInfo = [];
		protected readonly List<Type> _openTypeInfo = [];

		protected TypeIndex(IEnumerable<Type> collection, Func<Type, bool> predicate)
		{
			foreach (var type in collection)
			{
				if (type.IsGenericTypeDefinition)
				{
					if (type.GetInterfaces().Any(predicate))
					{
						_openTypeInfo.Add(type);
					}
				}
				else
				{
					foreach (var @interface in type.GetInterfaces().Where(predicate))
					{
						(_closedTypeInfo.TryGetValue(@interface, out var list) ? list : _closedTypeInfo[@interface] = []).Add(type);
					}
				}
			}
		}

		public IEnumerable<T> Resolve<T>(IServiceProvider services)
		{
			return (IEnumerable<T>)_cache.GetOrAdd(typeof(T), CreateResolverFactory<T>)(services);
		}

		protected abstract IReadOnlyList<Type> IsAssignableTo(Type type);

		private Func<IServiceProvider, IEnumerable<T>> CreateResolverFactory<T>(Type @interface)
		{
			var list = IsAssignableTo(@interface);
			return ResolverFactory;

			IEnumerable<T> ResolverFactory(IServiceProvider services)
			{
				foreach (var type in list)
				{
					yield return (T)ActivatorUtilities.GetServiceOrCreateInstance(services, type);
				}
			}
		}
	}

	internal static bool IsValidatorType(Type type)
	{
		return type.IsGenericType && type.GetGenericTypeDefinition() == typeof(IValidator<>);
	}

	private sealed class ValidatorTypeIndex(IEnumerable<Type> collection)
		: TypeIndex(collection, IsValidatorType)
	{
		protected override IReadOnlyList<Type> IsAssignableTo(Type @interface)
		{
			var result = new List<Type>();

			foreach (var kvp in _closedTypeInfo)
			{
				if (@interface.IsAssignableFrom(kvp.Key))
				{
					result.AddRange(kvp.Value);
				}
			}

			var validatedType = @interface.GetGenericArguments()[0];

			foreach (var type in _openTypeInfo)
			{
				try
				{
					// open type case one: Validator<T> : IValidator<T>
					// We try to close it with the validated type.
					var impl = type.MakeGenericType(validatedType);
					if (impl.IsAssignableTo(@interface))
					{
						result.Add(impl);
					}
				}
				catch (ArgumentException)
				{
				}

				try
				{
					// open type case two: Validator<T> : IValidator<Wrapper<T>>
					// If the validated type is generic, we try to close the validator with the validated type's generic arguments.
					if (validatedType.IsGenericType)
					{
						var impl = type.MakeGenericType(validatedType.GetGenericArguments());
						if (impl.IsAssignableTo(@interface))
						{
							result.Add(impl);
						}
					}
				}
				catch (ArgumentException)
				{
				}
			}

			return result;
		}
	}
}