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

using Gamecraft.Blocks.BlockGroups;
using Unity.Mathematics;
using UnityEngine;

using GamecraftModdingAPI.Blocks;
using GamecraftModdingAPI.Utility;

namespace GamecraftModdingAPI
{
    /// <summary>
    /// A group of blocks that can be selected together. The placed version of blueprints.
    /// </summary>
    public class BlockGroup : ICollection<Block>
    {
        internal static BlueprintEngine _engine = new BlueprintEngine();
        public int Id { get; }
        private readonly Block sourceBlock;
        private readonly List<Block> blocks;
        private float3 position, rotation;
        internal bool PosAndRotCalculated;

        internal BlockGroup(int id, Block block)
        {
            if (id == BlockGroupUtility.GROUP_UNASSIGNED)
                throw new BlockException("Cannot create a block group for blocks without a group!");
            Id = id;
            sourceBlock = block;
            blocks = new List<Block>(GetBlocks());
        }
        
        /// <summary>
        /// The position of the block group (center). Recalculated if blocks have been added/removed since the last query.
        /// </summary>
        public float3 Position
        {
            get
            {
                if (!PosAndRotCalculated)
                    Refresh();
                return position;
            }
            set
            {
                var diff = value - position;
                foreach (var block in blocks)
                    block.Position += diff;
                if (!PosAndRotCalculated) //The condition can only be true if a block has been added/removed manually
                    Refresh(); //So the blocks array is up to date
                else
                    position += diff;
            }
        }

        /// <summary>
        /// The rotation of the block group. Recalculated if blocks have been added/removed since the last query.
        /// </summary>
        public float3 Rotation
        {
            get
            {
                if (!PosAndRotCalculated)
                    Refresh();
                return rotation;
            }
            set
            {
                var diff = value - rotation;
                var qdiff = Quaternion.Euler(diff);
                foreach (var block in blocks)
                {
                    block.Rotation += diff;
                    block.Position = qdiff * block.Position;
                }
                if (!PosAndRotCalculated)
                    Refresh();
                else
                    rotation += diff;
            }
        }

        /*/// <summary>
        /// Removes all of the blocks in this group from the world.
        /// </summary>
        public void RemoveBlocks()
        {
            _engine.RemoveBlockGroup(Id); - TODO: Causes a hard crash
        }*/

        /// <summary>
        /// Creates a new block group consisting of a single block.
        /// You can add more blocks using the Add() method or by setting the BlockGroup property of the blocks.<br />
        /// Note that only newly placed blocks should be added to groups.
        /// </summary>
        /// <param name="block">The block to add</param>
        /// <returns>A new block group containing the given block</returns>
        public static BlockGroup Create(Block block)
        {
            return new BlockGroup(_engine.CreateBlockGroup(default, default), block);
        }

        /// <summary>
        /// Collects each block that is a part of this group. Also sets the position and rotation.
        /// </summary>
        /// <returns>An array of blocks</returns>
        private Block[] GetBlocks()
        {
            if (!sourceBlock.Exists) return new[] {sourceBlock}; //The block must exist to get the others
            var ret = _engine.GetBlocksFromGroup(sourceBlock.Id, out var pos, out var rot);
            position = pos;
            rotation = ((Quaternion) rot).eulerAngles;
            PosAndRotCalculated = true;
            return ret;
        }

        private void Refresh()
        {
            blocks.Clear();
            blocks.AddRange(GetBlocks());
        }

        internal static void Init()
        {
            GameEngineManager.AddGameEngine(_engine);
        }

        public IEnumerator<Block> GetEnumerator() => blocks.GetEnumerator();
        IEnumerator IEnumerable.GetEnumerator() => blocks.GetEnumerator();

        /// <summary>
        /// Adds a block to the group. You should only add newly placed blocks
        /// so that the game initializes the group membership properly.
        /// </summary>
        /// <param name="item"></param>
        /// <exception cref="NullReferenceException"></exception>
        public void Add(Block item)
        {
            if (item == null) throw new NullReferenceException("Cannot add null to a block group");
            item.BlockGroup = this; //Calls AddInternal
        }

        internal void AddInternal(Block item) => blocks.Add(item);

        /// <summary>
        /// Removes all blocks from this group.
        /// You should not remove blocks that have been initialized, only those that you placed recently.
        /// </summary>
        public void Clear()
        {
            while (blocks.Count > 0)
                Remove(blocks[blocks.Count - 1]);
        }

        public bool Contains(Block item) => blocks.Contains(item);
        public void CopyTo(Block[] array, int arrayIndex) => blocks.CopyTo(array, arrayIndex);

        /// <summary>
        /// Removes a block from this group.
        /// You should not remove blocks that have been initialized, only those that you placed recently.
        /// </summary>
        /// <param name="item"></param>
        /// <returns></returns>
        /// <exception cref="NullReferenceException"></exception>
        public bool Remove(Block item)
        {
            if (item == null) throw new NullReferenceException("Cannot remove null from a block group");
            bool ret = item.BlockGroup == this;
            if (ret)
                item.BlockGroup = null; //Calls RemoveInternal
            return ret;
        }

        internal void RemoveInternal(Block item) => blocks.Remove(item);

        public int Count => blocks.Count;
        public bool IsReadOnly { get; } = false;

        public Block this[int index] => blocks[index]; //Setting is not supported, since the order doesn't matter
    }
}