using System;
using Svelto.DataStructures;
using Svelto.ECS;
using Svelto.ECS.Hybrid;
using Svelto.ECS.Internal;

namespace TechbloxModdingAPI.Utility
{
    public readonly ref struct RefCollection<T> where T : struct, IBaseEntityComponent
    {
        private readonly bool managed;
        private readonly int count;
        private readonly NB<T> nativeArray;
        private readonly MB<T> managedArray;
        private readonly NativeEntityIDs nativeIDs;
        private readonly ManagedEntityIDs managedIDs;
        private readonly ExclusiveGroupStruct group;

        public RefCollection(int count, MB<T> managedArray, ManagedEntityIDs managedIDs, ExclusiveGroupStruct group)
        {
            this.count = count;
            this.managedArray = managedArray;
            this.managedIDs = managedIDs;
            this.group = group;
            managed = true;
            nativeArray = default;
            nativeIDs = default;
        }

        public RefCollection(int count, NB<T> nativeArray, NativeEntityIDs nativeIDs, ExclusiveGroupStruct group)
        {
            this.count = count;
            this.nativeArray = nativeArray;
            this.nativeIDs = nativeIDs;
            this.group = group;
            managed = false;
        }

        public Enumerator GetEnumerator() => new(this);
        
        /// <summary>
        /// The amount of items in the collection.
        /// </summary>
        public int Count => count;

        public T[] ToArray() => ToArray(a => a.Component);

        public TA[] ToArray<TA>(Func<(T Component, EGID ID), TA> transformFunction, Predicate<(T Component, EGID ID)> predicateFunction = null)
        {
            var result = new TA[Count];
            int i = 0;
            foreach (var opt in this)
            {
                if (predicateFunction != null && !predicateFunction((opt.Get(), opt.EGID))) continue;
                result[i] = transformFunction((opt.Get(), opt.EGID));
                i++;
            }

            return result;
        }

        public ref struct Enumerator
        {
            private RefCollection<T> coll;
            private int index;

            public Enumerator(RefCollection<T> collection)
            {
                index = -1;
                coll = collection;
            }

            public OptionalRef<T> Current
            {
                get
                {
                    if (coll.count <= index && index >= 0) return default;
                    if (coll.managed)
                        return new OptionalRef<T>(coll.managedArray, (uint)index,
                            new EGID(coll.managedIDs[index], coll.group));
                    return new OptionalRef<T>(coll.nativeArray, (uint)index,
                        new EGID(coll.nativeIDs[index], coll.group));
                }
            }

            public bool MoveNext()
            {
                return ++index < coll.count;
            }
        }
    }
}