#if NET5_0_OR_GREATER
using Microsoft.Extensions.DependencyInjection;
#endif

namespace BITKit.Packages.Core.LazyLoad
{
    public interface ILazyLoad
    {
        bool IsLoaded { get; }
    }

    public interface ILazyLoad<T> : ILazyLoad
    {
        T Value { get; }
        bool TryGetValue(ref T value);
    }

    public abstract class LazyLoad<T> : ILazyLoad<T>
    {
        public bool IsLoaded
        {
            get
            {
                if (_value is null)
                    Load();
                return _value is not null;
            }
        }

        private T _value;

        public T Value
        {
            get
            {
                if (_value is null)
                    Load();
                return _value;
            }
            protected set => _value = value;
        }

        public bool TryGetValue(ref T value)
        {
            if (IsLoaded)
            {
                value = Value;
                return true;
            }

            Load();
            return false;
        }

        protected abstract void Load();
    }

#if NET5_0_OR_GREATER
    public class ServiceLoader<T> : LazyLoad<T>
    {
        protected override void Load()
        {
            if (BITApp.ServiceProvider is null) return;
            if (BITApp.ServiceCollection is null) return;
            var service = BITApp.ServiceProvider.GetService<T>();
            if (service is null) return;
            Value = service;
        }
    }
#endif
}