using System;
using System.Collections.Generic;
using Svelto.ECS;
using Svelto.Tasks;
using Svelto.Tasks.Lean;
using TechbloxModdingAPI.Tasks;

namespace TechbloxModdingAPI.Utility
{
    public static class NativeApiExtensions
    {
        /// <summary>
        /// Attempts to query an entity and returns an optional that contains the result if succeeded.
        /// <b>This overload does not take initializer data into account.</b>
        /// </summary>
        /// <param name="entitiesDB">The entities DB</param>
        /// <param name="egid">The EGID to query</param>
        /// <typeparam name="T">The component type to query</typeparam>
        /// <returns>An optional that contains the result on success or is empty if not found</returns>
        public static OptionalRef<T> QueryEntityOptional<T>(this EntitiesDB entitiesDB, EGID egid)
            where T : unmanaged, IEntityComponent
        {
            return entitiesDB.TryQueryEntitiesAndIndex<T>(egid, out uint index, out var array)
                ? new OptionalRef<T>(array, index)
                : new OptionalRef<T>(); 
        }

        /// <summary>
        /// Attempts to query an entity and returns the result in an optional reference.
        /// </summary>
        /// <param name="entitiesDB">The entities DB to query from</param>
        /// <param name="obj">The ECS object to query</param>
        /// <param name="group">The group of the entity if the object can have multiple</param>
        /// <typeparam name="T">The component to query</typeparam>
        /// <returns>A reference to the component or a dummy value</returns>
        public static OptionalRef<T> QueryEntityOptional<T>(this EntitiesDB entitiesDB, EcsObjectBase obj, ExclusiveGroupStruct group = default)
            where T : unmanaged, IEntityComponent
        {
            EGID id = group == ExclusiveGroupStruct.Invalid ? obj.Id : new EGID(obj.Id.entityID, group);
            var opt = QueryEntityOptional<T>(entitiesDB, id);
            return opt ? opt : new OptionalRef<T>(obj, true);
        }

        /// <summary>
        /// Attempts to query an entity and returns the result or a dummy value that can be modified.
        /// </summary>
        /// <param name="entitiesDB">The entities DB to query from</param>
        /// <param name="obj">The ECS object to query</param>
        /// <param name="group">The group of the entity if the object can have multiple</param>
        /// <typeparam name="T">The component to query</typeparam>
        /// <returns>A reference to the component or a dummy value</returns>
        public static ref T QueryEntityOrDefault<T>(this EntitiesDB entitiesDB, EcsObjectBase obj, ExclusiveGroupStruct group = default)
            where T : unmanaged, IEntityComponent
        {
            EGID id = group == ExclusiveGroupStruct.Invalid ? obj.Id : new EGID(obj.Id.entityID, group);
            var opt = QueryEntityOptional<T>(entitiesDB, id);
            if (opt) return ref opt.Get();
            if (obj.InitData.Valid) return ref obj.InitData.Initializer(id).GetOrAdd<T>();
            /*if (!obj.InitData.Valid) return ref opt.Get(); //Default value
            var init = obj.InitData.Initializer(id);
            // Do not create the component if missing, as that can trigger Add() listeners that, in some cases, may be
            // invalid if (ab)using the classes in an unusual way - TODO: Check entity descriptor or something
            if (init.Has<T>()) return ref init.Get<T>();*/
            return ref opt.Get(); //Default value
        }

        private static readonly Dictionary<Type, (int PublishedCount, HashSet<EGID> Changes)> ChangesToPublish = new();

        /// <summary>
        /// Publishes an entity change, ignoring duplicate publishes and delaying changes as necessary.
        /// It will only publish in the next frame.
        /// </summary>
        /// <param name="entitiesDB">The entities DB to publish to</param>
        /// <param name="id">The ECS object that got changed</param>
        /// <param name="limit">Limits how many changes to publish - should be no more than the consumers' capacity that process this component</param>
        /// <typeparam name="T">The component that changed</typeparam>
        public static void PublishEntityChangeDelayed<T>(this EntitiesDB entitiesDB, EGID id, int limit = 80)
            where T : unmanaged, IEntityComponent
        { //TODO: Doesn't seem to help
            if(!ChangesToPublish.ContainsKey(typeof(T)))
                ChangesToPublish.Add(typeof(T), (0, new HashSet<EGID>()));
            var changes = ChangesToPublish[typeof(T)].Changes;
            if (changes.Contains(id)) return;
            changes.Add(id);
            PublishChanges<T>(entitiesDB, id, limit).RunOn(Scheduler.leanRunner);
        }

        private static IEnumerator<TaskContract> PublishChanges<T>(EntitiesDB entitiesDB, EGID id, int limit)
            where T : unmanaged, IEntityComponent
        {
            yield return Yield.It;
            while (ChangesToPublish[typeof(T)].PublishedCount >= limit)
                yield return Yield.It;
            entitiesDB.PublishEntityChange<T>(id);
            var (count, changes) = ChangesToPublish[typeof(T)];
            changes.Remove(id);
            ChangesToPublish[typeof(T)] = (count + 1, changes);
            yield return Yield.It;
            ChangesToPublish[typeof(T)] = (0, changes);
        }
    }
}