using System;
using System.Collections.Generic;
using System.Linq;

namespace Cryville.Crtr.Browsing.Actions {
	public class ActionManager {
		readonly Dictionary<Type, List<IResourceAction>> _actions = new();
		readonly Dictionary<IResourceAction, int> _refCounts = new();

		public event Action Changed;

		class ActionPriorityComparer : IComparer<IResourceAction> {
			public static readonly ActionPriorityComparer Instance = new();
			public int Compare(IResourceAction x, IResourceAction y) {
				return x.Priority.CompareTo(y.Priority);
			}
		}

		void Register(Type type, IResourceAction action) {
			if (!_actions.TryGetValue(type, out List<IResourceAction> actions)) {
				_actions.Add(type, actions = new List<IResourceAction>());
			}
			int index = actions.BinarySearch(action, ActionPriorityComparer.Instance);
			if (index < 0) index = ~index;
			actions.Insert(index, action);
			if (_refCounts.ContainsKey(action)) _refCounts[action]++;
			else _refCounts[action] = 1;
			Changed?.Invoke();
		}
		public void Register(IResourceAction action) {
			Register(typeof(object), action);
		}
		public void Register<T>(IResourceAction<T> action) where T : IResourceMeta {
			Register(typeof(T), action);
		}

		public void Unregister(Type type, IResourceAction action) {
			if (!_actions.TryGetValue(type, out List<IResourceAction> actions)) return;
			if (--_refCounts[action] > 0) return;
			actions.Remove(action);
			Changed?.Invoke();
		}
		public void Unregister(IResourceAction action) {
			Unregister(typeof(object), action);
		}
		public void Unregister<T>(IResourceAction<T> action) where T : IResourceMeta {
			Unregister(typeof(T), action);
		}

		public IEnumerable<IResourceAction> GetActions(Uri uri, IResourceMeta res) {
			return GetActions(uri, res, res.GetType());
		}
		IEnumerable<IResourceAction> GetActions(Uri uri, IResourceMeta res, Type type) {
			if (type == null) return Enumerable.Empty<IResourceAction>();
			IEnumerable<IResourceAction> result;
			if (_actions.TryGetValue(type, out List<IResourceAction> actions))
				result = actions.Where(i => i.CanInvoke(uri, res));
			else
				result = Enumerable.Empty<IResourceAction>();
			if (type != typeof(object))
				result = result
					.Concat(GetActions(uri, res, type.BaseType))
					.Concat(type.GetInterfaces().SelectMany(i => GetActions(uri, res, i)));
			return result;
		}
	}
}