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

namespace TechbloxModdingAPI.Utility.ECS
{
    public static partial 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 initializing the entity, check if the component is allowed by the descriptor, otherwise it could cause
            // issues in the game with Add() calls running unexpectedly
            if (obj.InitData.Valid && obj.AllowedEntityComponents.Contains(typeof(T)))
                return ref obj.InitData.Initializer(id).GetOrAdd<T>();
            return ref opt.Get(); //Default value
        }

        /// <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>
        /// <typeparam name="T">The component that changed</typeparam>
        public static void PublishEntityChangeDelayed<T>(this EntitiesDB entitiesDB, EGID id)
            where T : unmanaged, IEntityComponent
        {
            PublishChanges<T>(entitiesDB, id).RunOn(Scheduler.leanRunner);
        }

        private static IEnumerator<TaskContract> PublishChanges<T>(EntitiesDB entitiesDB, EGID id)
            where T : unmanaged, IEntityComponent
        {
            yield return Yield.It;
            var entityStream = entitiesDB.GetEntityStream<T>();
            if (entityStream is null)
                yield break; // There is no entity stream for this type
            var consumers = entityStream.GetConsumers();
            if (consumers == null)
            {
                Console.WriteLine("Consumers is null");
                yield break;
            }

            bool waitForConsumers;
            do
            {
                waitForConsumers = false;
                for (int i = 0; i < consumers.count; i++)
                {
                    var buffer = consumers[i].GetRingBuffer();
                    if (buffer.Count + 1 <= buffer.Capacity) continue;
                    waitForConsumers = true;
                    break;
                }

                if (waitForConsumers) yield return Yield.It;
            } while (waitForConsumers);
            entitiesDB.PublishEntityChange<T>(id);
        }

        /// <summary>
        /// Query entities as OptionalRefs. The elements always exist, it's just a nice way to encapsulate the data.
        /// </summary>
        /// <param name="entitiesDB"></param>
        /// <param name="group"></param>
        /// <param name="select"></param>
        /// <typeparam name="T"></typeparam>
        /// <typeparam name="TR"></typeparam>
        /// <returns></returns>
        public static RefCollection<T> QueryEntitiesOptional<T>(this EntitiesDB entitiesDB, ExclusiveGroupStruct group) where T : unmanaged, IEntityComponent
        {
            var (buffer, ids, count) = entitiesDB.QueryEntities<T>(group);
            return new RefCollection<T>(count, buffer, ids, group);
        }
    }
}